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The rapid emergence of organic-inorganic lead halide perovskites for low-cost and high-efficiency photovoltaics promises to impact new photovoltaic concepts. Their high power conversion efficiencies, ability to coat perovskite layers on glass via various scalable deposition techniques, excellent optoelectronic properties and synthetic versatility for modulating transparency and colour, allows perovskite solar cells (PSCs) to be an ideal solution for building-integrated photovoltaics (BIPV) which transforms windows or facades into electric power generators. In this review, the unique features and properties of PSCs for BIPV application are accessed. Device engineering and optical management strategies of active layers, interlayers and electrodes for semi-transparent, bifacial and colourful PSCs are also discussed. The performance of PSCs under conditions that are relevant for BIPV such as different operational temperature, light intensity and light incident angle are also reviewed. Recent outdoor stability testing of PSCs in different countries and other demonstration of scalability and deployment of PSCs are also spotlighted. Finally, the current challenges and future opportunities for realising perovskite based BIPV are discussed. This article is protected by copyright. All rights reserved.

In the past few years, a large variety of perovskite solar cells (PSCs) with vivid and well-distinguished color hues have been demonstrated. In this Perspective, we compare different strategies employed to realize colorful PSCs both in opaque and semitransparent designs. The approaches used to modulate the PSCs' colorful appearance can be divided into two main categories: the first one based on the modifications of their internal layers (i.e., absorber, electron- and/or hole-transporting layers, and electrodes), while the second is based on the addition of external colored or nanostructured films to the standard PSCs. The advantages and bottlenecks of each strategy are discussed in terms of PSCs' color tunability, transparency, photovoltaic performances, fabrication processes feasibility, and scalability, in view of suitable applications in an urban context for building-integrated photovoltaics. National Research Foundation (NRF) Accepted version This research is supported by the National Research Foundation, Prime Minister’s Office, Singapore under Energy Innovation Research Program (Grant numbers: NRF2015EWT-EIRP003-004, NRF-CRP14-2014-03, Solar CRP: S18-1176-SCRP, NRF2018- ITC001-001).

Inorganic cesium lead halide perovskite nanocrystals are promising materials for optoelectronic applications as they exhibit high thermal stability alongside precise color tunability and high color purity; however, their optical properties are degraded by surface defects. This work demonstrates a room temperature synthesis of CsPbBr3 nanocrystals facilitating in situ surface passivation via the incorporation of Zn2+ cations. The facile incorporation ZnBr2 into the precursor solution facilitates Zn2+ and Br− substitution into the nanocrystal surface/subsurface layers to induce passivation of existing Pb2+ and Br– vacancies and increase the photoluminescence quantum yield from ∼48 to 86%. The XPS and solid-state 1H MAS NMR techniques show that the key modification is a reduction of the octylamine:oleic acid ratio leading to a near-neutral surface charge; this is accompanied by the appearance of larger nanosheets and nanowires observed by quantitative powder XRD and HR-TEM. The suitability of these perovskite nanocrystals for electrically driven applications was confirmed by the fabrication of light-emitting diodes, which demonstrate that the in situ Zn2+ passivation strategy enhanced the external quantum efficiency by ∼60%. National Research Foundation (NRF) PV acknowledges a Presidential Postdoctoral Fellowship from Nanyang Technological University (NTU), Singapore via grant 04INS000581C150OOE01. We acknowledge financial support from the Singapore National Research Foundation, Prime Minister’s Office, through the Competitive Research Program (CRP Award No. NRF-CRP14-2014-03). The authors would like to acknowledge the Facility for Analysis, Characterization, Testing and Simulation (FACTS) at NTU, Singapore, for use of their electron microscopy and X-ray diffraction facilities. We would also like to acknowledge the NTU Center of High Field NMR Spectroscopy and Imaging for the use of their NMR facilities. The authors would also like to thank Prof. Nripan Mathews and Dr. Nur Fadilah Jamaludin for the valuable discussion, Mr. Sai S. H. Dintakurti for discussions with aspects of the crystallographic analysis and Mr. Gautam V. Nutan for assistance with the XPS measurements. JVH acknowledges financial support for the solid state NMR instrumentation at Warwick used in this research which was funded by EPSRC (grants EP/M028186/1 and EP/K024418/1), the University of Warwick, and the Birmingham Science City AM1 and AM2 projects which were supported by Advantage West Midlands (AWM) and the European Regional Development Fund (ERDF). AAMB acknowledges the Tizard studentship from the Faculty of Engineering and Physical Sciences at University of Southampton.

Recent advances in Ruddlesden–Popper (RP) perovskites have shown highly efficient light-emitting diodes (LEDs) due to the energy confinement by an energy cascade from the quasi-2D (donors) to 3D (acceptors) states. This is achieved by forming mixed-dimensional phases using 2D templating (spacer) molecules. The effect of the spacer molecular design on the efficacy of light emission is hitherto unknown, thus motivating this study into eight different spacer molecules ranging from the naphthyl to phenyl alkyl families. The phase distribution, which influences the resultant energy landscape, can simply be modulated by the choice of this spacer molecule. It was found that a high acceptor-to-donor ratio is required to achieve the best LED efficiencies. A simple absorption spectroscopy measurement can also be employed to screen potential RP systems. The findings are of significance to other halide perovskites and lay down a useful guideline to assess new spacer molecules for more efficient RP perovskite LEDs. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version This research was supported by the National Research Foundation, Prime Minister’s Office, Singapore, under its Competitive Research Programme (CRP Award No. NRFCRP14- 2014-03) and Intra-CREATE Collaborative Grant (NRF2018-ITC001-001). T.C.S. and D.G. acknowledge the financial support from the Tier 2 grant MOE2017-T2-2-002; and from the Singapore National Research Foundation Investigatorship NRF-NRFI-2018-04.

Lead-free halide perovskite semiconductors are necessary due to the atmospheric instability and lead toxicity associated with the 3D lead halide perovskites. However, a stable lead-free perovskite with an ideal band gap (1.2-1.4 eV) for photovoltaics is still missing. In this work, we synthesized organic-inorganic gold halide double perovskites ((CH3NH3)2Au2X6, X = Br, I) through a solution-processed route that offers an ideal direct band gap for photovoltaic applications. Density functional theory calculations confirm the direct nature of the band gap with reasonable absorption coefficients in the visible range and excellent charge transport properties. In addition, the Au-halide perovskites show high chemical stability and photoresponse. These combined properties demonstrate that Au-based halide perovskites can be a promising group of compounds for optoelectronic applications. National Research Foundation (NRF) Accepted version This research was supported by the National Research Foundation, Prime Minister’s Office, Singapore, under its Competitive Research Programme (CRP Award No. NRF- 482 CRP14-2014-03) and Intra-CREATE Collaborative Grant (NRF2018-ITC001-001). We would also like to thank Dr. Li Yongxin for helping us solve the crystal structures of the materials presented herein.

High performance organic nano-floating gate transistor memory (NFGTM) has important prerequisites of low processing temperature, solution–processable layers and charge trapping medium with high storage capacity. We demonstrate organic NFGTM using black phosphorus quantum dots (BPQDs) as a charge trapping medium by simple spin-coating and low processing temperature (< 120 °C). The BPQDs with diameter of 12.6 ± 1.5 nm and large quantum confined bandgap of ~2.9 eV possess good charge trapping ability. The organic memory device exhibits excellent memory performance with a large memory window of 61.3 V, write-read-erase-read cycling endurance of 10 3 for more than 180 cycles and reliable retention over 10,000 sec. In addition, we successfully improved the memory retention to ON/OFF current ratio > 10 4 over 10,000 sec by introducing PMMA as the tunneling layer. ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Accepted version

Perovskite semiconductors have experienced meteoric rise in a variety of optoelectronic applications. With a strong foothold on photovoltaics, much focus now lies on their light emission applications. Rapid progress in materials engineering have led to the demonstration of external quantum efficiencies that surpass the previously established theoretical limits. However, there remains much scope to further optimize the light propagation inside the device stack through careful tailoring of the optical processes that take place at the bulk and interface levels. Photon recycling in the emitter material followed by efficient outcoupling can result in boosting external efficiencies up to 100%. In addition, the poor ambient and operational stability of these materials and devices restrict further commercialization efforts. With best operational lifetimes of only a few hours reported, there is a long way to go before perovskite LEDs can be perceived as reliable alternatives to more established technologies like organic or quantum dot-based LED devices. This review article starts with the discussions of the mechanism of luminescence in these perovskite materials and factors impacting it. It then looks at the possible routes to achieve efficient outcoupling through nanostructuring of the emitter and the substrate. Next, we analyze the instability issues of perovskite-based LEDs from a photophysical standpoint, taking into consideration the underlying phenomena pertaining to defects, and summarize recent advances in mitigating the same. Finally, we provide an outlook on the possible routes forward for the field and propose new avenues to maximally exploit the excellent light-emitting capabilities of this family of semiconductors. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) National Research Foundation (NRF) Published version This research was supported by National Research Foundation, Prime Minister’s Office, Singapore, under its Competitive Research Programme (CRP Award No. NRFCRP14-2014-03), and Intra-CREATE Collaborative Grant (NRF2018-ITC001-001), as well as Ministry of Education (MOE) under AcRF Tier 2 grants (2018-T2-1-075 and 2019-T2-2-106), and A*STAR National Robotics Programme (W1925d0106).

Slow hot carrier cooling in halide perovskites holds the key to the development of hot carrier (HC) perovskite solar cells. For accurate modeling and pragmatic design of HC materials and devices, it is essential that HC temperatures are reliably determined. A common approach involves fitting the high-energy tail of the main photobleaching peak in a transient absorption spectrum with a Maxwell-Boltzmann distribution. However, this approach is problematic because of complications from the overlap of several photophysical phenomena and a lack of consensus in the community on the fitting procedures. Herein, we propose a simple approach that circumvents these challenges. Through tracking the broadband spectral evolution and accounting for bandgap renormalization and spectral line width broadening effects, our method extracts not only accurate and consistent carrier temperatures but also other important parameters such as the quasi-Fermi levels, bandgap renormalization constant, etc. Establishing a reliable method for the carrier temperature determination is a step forward in the study of HCs for next-generation perovskite optoelectronics. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

Metal halide perovskites have affirmed their pedigree as extraordinary semiconducting materials, exhibiting properties rivalling those observed in single crystal compound semiconductors. Perovskites show tremendous versatilities in both structure and composition tuning, and therefore applications ranging from optoelectronics to X-ray imaging and spintronics, neuromorphic electronics are emerging. Moreover, when their dimensions become comparable to the exciton Bohr radius, perovskite nanostructures and layered systems display remarkable properties because of quantum confinement. Nanostructured and lower dimensional layered perovskites exhibit properties that are yet to be fully exploited such as extraordinarily high luminescence, narrow emissions, high exciton binding energies, strong non-linear phenomena, and carrier cascade characteristics. This review, while highlighting the frontier phenomena that continue to be unravelled, outlines how confined structures of these materials have demonstrated properties that promise to unlock exceptional quantum phenomena to challenge the optoelectronic limits. Accepted version

Successful adoption of defect management and carrier confinement strategies in Ruddlesden-Popper (RP) perovskites has driven the impressive improvements to performance of perovskite-based light-emitting diodes (PeLEDs) seen to date. Although functional additives have been advantageous in mitigating defects, their influence over crystallization behavior of RP (L2Am-1PbmX3m+1) perovskites has yet to be fully studied. This is especially important for blue-emitting mono-halide RP perovskites, where stringent control over m domain distribution is needed for efficient PeLEDs. Herein, we investigate the effect of tri-phenyl-phosphine-oxide (TPPO) on crystallization behaviour of blue RP (PBA2Csm-1PbmBr3m+1) perovskites. Despite TPPO addition, its absence in the resulting film eliminates its role as a passivating agent. Instead, TPPO acts as crystallization and phase distribution modulator – promoting the formation of a narrow distribution of higher m domains with higher Br content. In doing so, an enhancement of ~35% was noted with champion device yielding efficiency of 3.8% at λ of 483 nm. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version This research was funded by Ministry of Education, Singapore (MOE2018-T2-2-083) and (MOE2019-T2-2-097). The photophysical measurements are made possible through the support from the Ministry of Education, Singapore under its AcRF Tier 2 grant MOE-T2EP50120-0004, and the National Research Foundation, Singapore under its NRF Investigatorship (NRF-NRFI2018-04). We acknowledge the Facility for Analysis, Characterization, Testing and Simulation, Nanyang Technological University, Singapore, for use of their electron microscopy/X-ray facilities.

Hybrid metal halide perovskite solar cells (PSCs) have consistently demonstrated high power conversion efficiency (PCE), although the best performing PSCs mostly employ high-temperature (500 oC) processed compact and mesoporous TiO2. Instead, low-temperature processed PSCs are desirable for implementation on flexible substrates and tandem solar cells. Here, we present a new method to achieve high efficiency flexible planar PSCs based on a low-temperature processed nonaqueous sol-gel route synthesized TiO2 and a guanidinium iodide (GuaI) salt passivation treatment of the perovskite film. We fabricate both rigid and flexible triple-cation perovskite (Cs0.05 (MA0.17FA0.83)0.95Pb(I0.85Br0.15)3, Eg ~1.58 eV) PSCs, achieving PCEs of 19.8% and 17.0% on glass and polyethylene naphtholate, (PEN) substrates respectively. At the same time, rigid and flexible high-bandgap double cation (FA0.85Cs0.15Pb(I0.7Br0.3)3, Eg ~1.72 eV) PSCs reached a PCE of 18.0 % and of 15.8%. Moreover, large area (1cm2) ~1.58 eV and ~1.72 eV-PSCs achieved PCEs of 18.2% and 16.7% PCE on glass substrates and of 16.2% and 13.9% on PEN substrates demonstrating the high uniformity of all the solar cell layers. NRF (Natl Research Foundation, S’pore) Accepted version

Recent progress of vapor-deposited perovskite solar cells (PSCs) has proved the feasibility of this deposition method in achieving promising photovoltaic devices. For the first time, it is probed the versatility of the co-evaporation process in creating perovskite layers customizable for different device architectures. A gradient of composition is created within the perovskite films by tuning the background chamber pressure during the growth process. This method leads to co-evaporated MAPbI3 film with graded Fermi levels across the thickness. Here it is proved that this growth process is beneficial for p-i-n PSCs as it can guarantee a favorable energy alignment at the charge selective interfaces. Co-evaporated p-i-n PSCs, with different hole transporting layers, consistently achieve power conversion efficiency (PCE) over 20% with a champion value of 20.6%, one of the highest reported to date. The scaled-up p-i-n PSCs, with active areas of 1 and 1.96 cm2, achieved the record PCEs of 19.1% and 17.2%, respectively, while the flexible PSCs reached a PCE of 19.3%. Unencapsulated PSCs demonstrate remarkable long-term stability, retaining ≈90% of their initial PCE when stored in ambient for 1000 h. These PSCs also preserve over 80% of their initial PCE after 500 h of thermal aging at 85 °C. © 2021 Wiley-VCH GmbH

Next-generation displays and lighting technologies require efficient optical sources that combine brightness, color purity, stability, substrate flexibility. Metal halide perovskites have potential use in a wide range of applications, for they possess excellent charge transport, bandgap tunability and, in the most promising recent optical source materials, intense and efficient luminescence. This review links metal halide perovskites' performance as efficient light emitters with their underlying materials electronic and photophysical attributes. Accepted version

Herein, we report Sn2+ doping in FAPbI3 NCs to stabilize the α-phase, while using propionic acid as a co-ligand. The Sn2+ doping enhances the emission quantum yield from 35% to 63% and dramatically improves the colloidal and phase stability. Also, we demonstrated the use of Sn doped FAPbI3 NCs in near-infrared (NIR) LEDs. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

Surface passivation has been proven to be an effective strategy to improve power conversion efficiency and stability of perovskite solar cells. However, the rationale for choosing an appropriate passivator, in terms of the type of interaction with the underlying perovskite layer, is still not clear yet. Here, we purposively choose two molecules as passivators for perovskites, fluorinated phosphonic acid and its corresponding phosphonate salt, to monitor the extent of interaction between these passivators and the perovskite surface. The effect of passivation on film stability and device performance is also determined. Higher photoluminescence intensity and longer carrier lifetime are observed in perovskite films that treated with phosphonium salt passivation because of the stronger interaction with perovskites. The corresponding device shows enhancement in power conversion efficiency from 18.27 to 19.44%. Furthermore, the water contact angle of passivated perovskite films exceeds 110.9° as compared to the pristine, untreated perovskite (74.5°). This superhydrophobic nature imparted by fluorinated phosphonium salt passivation enables excellent long-term stability of devices, allowing over 90% of their initial efficiency to be retained even after 90 days' storage under ambient conditions with 30% relative humidity. Ministry of Education (MOE) Nanyang Technological University National Research Foundation (NRF) The authors acknowledge funding from the National Research Foundation, Prime Minister's Office, Singapore, under its Intra-CREATE Collaborative Grant (NRF2018-ITC001-001), Competitive Research Program (CRP Award No. NRF-CRP14-2014-03), and Singapore-Berkeley Research Initiative for Sustainable Energy (SinBeRISE) CREATE Program, Office of Naval Research Global (ONRG-NICOP-N62909-17-1-2155), Nanyang Technological University start-up grants (M4080514 and M4081293); the Ministry of Education Academic Research Fund Tier 1 grants (RG184/14, RG166/16 and RG101/15), and Tier 2 grants (MOE2016-T2-1-100, MOE2014-T2-1-044, and MOE2015-T2-2-015). G. Han would like to acknowledge the support of the Fundamental Research Funds of Shandong University numbered 2019GN002.

Heterostructures, combining perovskite nanocrystals (PNC) and chalcogenide quantum dots, could pave a path to optoelectronic device applications by enabling absorption in the near-infrared region, tailorable electronic properties, and stable crystal structures. Ideally, the heterostructure host material requires a similar lattice constant as the guest which is also constrained by the synthesis protocol and materials selectivity. Herein, we present an efficient one-pot hot-injection method to synthesize colloidal all-inorganic cesium lead halide-lead sulfide (CsPbX3 (X = Cl, Br, I)-PbS) heterostructure nanocrystals (HNCs) via the epitaxial growth of the perovskite onto the presynthesized PbS nanocrystals (NCs). Optical and structural characterization evidenced the formation of heterostructures. The embedding of PbS NCs into CsPbX3 perovskite allows the tuning of the absorption and emission from 400 to 1100 nm by tuning the size and composition of perovskite HNCs. The CsPbI3-PbS HNCs show enhanced stability in ambient conditions. The stability, tunable optical properties, and variable band alignments accessible in this system would have implications in the design of novel optoelectronic applications such as light-emitting diodes, photodetectors, photocatalysis, and photovoltaics. Ministry of Education (MOE) Nanyang Technological University National Research Foundation (NRF) Accepted version M.J. acknowledges the National Research Foundation, Prime Minister’s Office, Singapore, under its Competitive Research Programme (CRP Award NRF-CRP14-2014-03). We acknowledge the Facility for Analysis, Characterization, Testing and Simulation, Nanyang Technological University, Singapore, for use of their electron microscopy/X-ray facilities. M.J. acknowledge National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2020R1A4A1019455). P.V. acknowledges a Presidential Postdoctoral Fellowship from Nanyang Technological University (NTU), Singapore, via Grant 04INS000581C150. We also acknowledge the NTU Centre of High Field NMR Spectroscopy and Imaging for the use of their NMR facilities. T.C.S. and J.W.M.L. acknowledge the financial support from the Singapore National Research Foundation through the NRF Investigatorship (NRF-NRFI-2018-04) and the Ministry of Education under its AcRF Tier 1 Grant RG91/19 and Tier 2 Grant MOE2019-T2-1-006.

One of the major bottlenecks of perovskite photovoltaic modules fabrication is the homogeneous deposition of perovskite material on large-area substrates. Here, we show that slot-die coating technique combined with synergistic gas quenching and substrate heating can produce compact, homogenous and reproducible Cs0.16FA0.84Pb(I0·88Br0.12)3 perovskite films. We demonstrate the fabrication of perovskite solar cells (PSCs) in a planar (n-i-p) device configuration and attain power conversion efficiency (PCE) of 18% over 0.09 cm2 device active area. The versatility of this crystallization strategy, which eliminates the need for complex solvents or additive engineering, was studied using planar SnO2- and TiO2-coated FTO substrates. Our study provides greater insights into achieving controlled coating and homogeneous crystallization of perovskite films over large-area substrates (~10 × 10 cm2) necessary for the commercialization of this technology. Ministry of Education (MOE) Nanyang Technological University National Research Foundation (NRF) Submitted/Accepted version This research was supported by NTU start-up grant (M4081866), Ministry of Education (MOE) under AcRF Tier 2 grants (2018-T2-1-075 and 2019-T2-2-106) and National Research Foundation, Prime Minister’s Office, Singapore, under Energy Innovation Research Program (grant numbers: NRF2015EWT-EIRP003-004 and Solar CRP: S18-1176- SCRP). This research was supported by a CEA CTBU funding, under PTC PrintRose project, and by the IDEX Mobility grant from Grenoble Alpes University (Com-UGA).

Halide perovskite nanocrystals are a promising candidate for lighting applications. However, the production of white light emitting diodes (LEDs) is still a major challenge due to halide ion segregation. In this work, it is demonstrated that reducing the thickness of the perovskite layer in an LED stack can modulate the recombination zone, such that a tunable emission can be obtained. This comprises of an orange electromer emission from a hole-transport layer (HTL), green electroluminescence from the perovskite active layer, and a blue monomer emission from the same HTL. Overall, a pure white emission can be achieved after successful device optimization, which is particularly challenging for LEDs in which the emission originates solely from perovskite layer. It is anticipated that this methodology could be employed on any type of green-emitting nanocrystals to fabricate white LEDs. Nanyang Technological University National Research Foundation (NRF) P.V. acknowledges a NTU, Singapore Presidential Postdoctoral Fellowship via grant 04INS00581C150. The authors acknowledge financial support from the Singapore National Research Foundation, Prime Minister’s Office, through the Competitive Research Program (CRP Award No. NRF-CRP14-2014-03).

Thermal evaporation is a very successful and widely adopted coating technique for the deposition of organic and inorganic materials on rough and textured surfaces and over large areas. Indeed, this technique is extensively used in the semiconductor industry for the fabrication of organic light emitting diodes (OLEDs) and is commonly used in displays. In the last few years, thermal evaporated perovskite solar cells (PSCs) have also shown the potential to reach high power conversion efficiency (PCE) both on small and over large area devices. In this work, we present a detailed optimization of the potassium-based surface treatment used to improve the performances of our MAPbI PSCs fabricated using the thermal co-evaporation technique. Small area planar n-i-p PSCs with an active area of 0.16 cm achieved PCEs above 19% and the large area PSCs with an active area of 1 cm reached 18.1%. These un-encapsulated PSCs also proved an excellent long-term shelf stability maintaining 90% of their initial PCEs for over six months when stored at ambient temperature. National Research Foundation (NRF) Published version This research is supported by the National Research Foundation, Prime Minister’s Office, Singaporeunder Energy Innovation Research Program (Grant numbers: NRF2015EWT-EIRP003-004, NRF-CRP14-2014-03, Solar CRP: S18-1176-SCRP, NRF2018-ITC001-001).

Realization of reduced ionic (cationic and anionic) defects at the surface and grain boundaries (GBs) of perovskite films is vital to boost the power conversion efficiency of organic-inorganic halide perovskite (OIHP) solar cells. Although numerous strategies have been developed, effective passivation still remains a great challenge due to the complexity and diversity of these defects. Herein, a solid-state interdiffusion process using multi-cation hybrid halide perovskite quantum dots (QDs) is introduced as a strategy to heal the ionic defects at the surface and GBs. It is found that the solid-state interdiffusion process leads to a reduction in OIHP shallow defects. In addition, Cs+ distribution in QDs greatly influences the effectiveness of ionic defect passivation with significant enhancement to all photovoltaic performance characteristics observed on treating the solar cells with Cs0.05 (MA0.17 FA0.83 )0.95 PbBr3 (abbreviated as QDs-Cs5). This enables power conversion efficiency (PCE) exceeding 21% to be achieved with more than 90% of its initial PCE retained on exposure to continuous illumination of more than 550 h. Nanyang Technological University National Research Foundation (NRF) N.M., S.G.M. would like to acknowledge funding from the Singapore National Research Foundation through the Intra-CREATE Collaborative Grant (NRF2018-ITC001-001). P.V. acknowledges Presidential Postdoctoral Fellowship visa grant M408070000.

Light management through low index medium, such as antireflective coating (ARC) provides practical solution to improve the efficiency of photovoltaics. However, a brute-force development of photonic structure on ARC is not necessarily useful, because of random scattering associated with impediment of light transmission. Here, we leverage the concept of disorder, rather than random, structured on ARC for improving efficiency without modifying original architecture of thin-film photovoltaics. We demonstrate a disordered polymer that leads to a total reflectance of 5% while demonstrating a high transmission of 94% across 300 to 820 nm wavelength. Next, we find that the arrangement of disordered points and line arrays constructing the polymer seems to be the key to control bandwidth performance of the ARC. Finally, we apply this into Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3 perovskite, and through experiments with wave-optics and full-device simulation, show a 1.6-fold absorption gain leading to 19.59% power-conversion-efficiency by the disordered ARC. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version This work is supported by the National Research Foundation, Prime Minister’s Office, Singapore under Energy Research Innovation Program (Grant number, NRF2015EWT-EIRP003-004 and NRF-CRP14-2014-03 and Solar CRP:S18-1176-SCRP), and Ministry of Education (MOE2016‐T2‐1‐052).

The rapid improvement in the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has prompted interest in bringing the technology toward commercialization. Capitalizing on existing industrial processes facilitates the transition from laboratory to production lines. In this work, we prove the scalability of thermally co-evaporated MAPbI3 layers in PSCs and mini-modules. With a combined strategy of active layer engineering, interfacial optimization, surface treatments, and light management, we demonstrate PSCs (0.16 cm2 active area) and mini-modules (21 cm2 active area) achieving record PCEs of 20.28% and 18.13%, respectively. Un-encapsulated PSCs retained ∼90% of their initial PCE under continuous illumination at 1 sun, without sample cooling, for more than 100 h. Looking toward tandem and building integrated photovoltaic applications, we have demonstrated semi-transparent mini-modules and colored PSCs with consistent PCEs of ∼16% for a set of visible colors. Our work demonstrates the compatibility of perovskite technology with industrial processes and its potential for next-generation photovoltaics. Accepted version

In recent years, hybrid lead-halide perovskites have emerged as promising solution-processed semiconductors for thin-film optoelectronics with a growing focus on light-emitting diode applications. Perovskites exhibit remarkable flexibilities in structure and composition tuning and possess excellent intrinsic properties such as band gap tunability over a visible range, high colour purity emission, high photoluminescence quantum yield (PLQY) and high exciton binding energies. Recently, perovskite-based light-emitting diodes (PeLEDs) have exhibited external quantum efficiency of 14.36% and revealed the potential for further improvement. High PLQY is a key requirement for better PeLED performance. This can be realised by controlling the grain-size of the perovskite films with optimum active layer thickness and utilising reduced-dimensionality perovskite emitters to spatially confine charge carriers for enhanced radiative recombination. In this short review, we discuss the critical parameters required for efficient PeLEDs, the recent progress mainly highlighting the energy transfer mechanism within Ruddlesden Popper structures and graded size nanoparticle films. We also outline the recommendations and strategies for further improvement. NRF (Natl Research Foundation, S’pore) Accepted version

Efficient perovskite light-emitting diodes are designed by employing an ordered vertical domain distribution in quasi-two-dimensional (quasi-2D) perovskites to induce better electron flow to the emitting domains. Dimethyl sulfoxide is added to the precursor solution to tune the crystallization rate and promote the formation of high-m domains near the substrate surface via the one-step deposition method. Optimized deposition conditions yielding a film with favorable energetic landscape for both carrier injection and confinement results in a 4-fold external quantum efficiency (EQE) enhancement with maximum EQE of 5.79%. Better carrier injection is further supported by a turn-on voltage value that is comparable to the band gap of the emitter material (∼2.25 eV).

Substituting expensive traditional hole transporting material (HTM) with cheaper inorganics is a key factor for perovskite photovoltaics commercialization. Cu2O is a promising p-type semiconductor exhibiting good band-alignment with perovskite. However, due to solvent and temperature incompatibility, Cu2O is typically employed in inverted configuration, where an even more expensive, unstable Phenyl-C61-butyric acid methyl ester is necessary as an electron-transporting layer. Therefore, we explored the use of sputtered nitrogen-doped Cu2O directly on halide-perovskite as a HTM. With a thin interfacial layer, efficiency of 15.73% was achieved. This work indicates the possibility of low cost sputtered inorganics as HTM for efficient perovskite photovoltaics. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

Although much of the initial progress in perovskite solar cells has been made by the archetypal CH3NH3PbI3, incorporation of an additional cation such as formamidinium, cesium, and mixed halides have shown promising results in both stability and device performance. However, the role of the additional cations as well as the mixed halides is yet to be fully understood. In this work, we investigate the role of different additives including group I alkali metal cations (K, Rb, Cs and NH4) and halide anions (Br and I) on double-cation perovskites, i.e., [(MAPbBr3)0.15(FAPbI3)0.85]. A notably longer charge carrier lifetime is achieved for perovskite films with additives and may be attributed to defect passivation. Selection rules are put forward based on the effect of the ionic size of an additive on phase stabilization and defect passivation. Addition of complementary size cation with respect to cation size of the parent perovskite, mainly helps stabilizing the perovskite phase by tuning tolerance factor, while addition of the similar size cation/anion, acts as defect passivator. The performance improvement of devices fabricated using NH4I as additive well supports this hypothesis, and offers yet another pathway toward harnessing the multitude of perovskite compositions to achieve high performing solar cells and perhaps other optoelectronic devices. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

Sub-micrometer cavities have been incorporated in the TiO2 photoanode of dye-sensitized solar cell to enhance its optical property with light scattering effect. These are large pores of several hundred nanometers in size and scatter incident light due to the difference refraction index between the scattering center and the surrounding materials, according to Mie theory. The pores are created using polystyrene (PS) or zinc oxide (ZnO) templates reported previously which resulted in ellipsoidal and spherical shapes, respectively. The effect of size and shape of scattering center was modeled using a numerical analysis finite-difference time-domain (FDTD). The scattering cross-section was not affected significantly with different shapes if the total displacement volume of the scattering center is comparable. Experiments were carried out to evaluate the optical property with varying size of ZnO templates. Photovoltaic effect of dye-sensitized solar cells made from these ZnO-assisted films were investigated with incident-photon-to-current efficiency to understand the effect of scattering center size on the enhancement of absorption. With 380 nm macropores incorporated, the power conversion efficiency has increased by 11% mostly thanks to the improved current density, while 170 nm and 500 nm macropores samples did not have increment in sufficiently wide range of absorbing wavelengths.

The synthesis of all-inorganic cesium lead halide perovskite quantum dots (QDs) typically requires high temperatures, stringent conditions, large quantities of surface ligands, and judicious purification steps to overcome ligand-induced charge injection barriers in optoelectronic devices. Low-temperature syntheses generally require lower ligand concentrations, but are severely limited by the low solubility of the Cs precursor. We describe an innovative and general approach under ambient conditions to overcome these solubility limitations, by employing crown ethers. The crown ethers facilitate complete dissolution of the CsBr precursor, rendering CsPbBr3 QD inks practical for device fabrication. The resultant LEDs displayed bright green emission, with a current efficiency, and external quantum efficiency of 9.22 cd A-1 and 2.64%, respectively. This represents the first LED based on CsPbBr3 QDs prepared at room temperature. Lastly, the crown ethers form core-shell structures, opening new avenues to exploit their strong coordination strength. NRF (Natl Research Foundation, S’pore) Accepted version

Lead (Pb) halide perovskites have attracted tremendous attention in recent years because of their rich optoelectronic properties, which have resulted in more than 22% power conversion efficient photovoltaics (PVs). Nevertheless, Pb-metal toxicity remains a huge hurdle for extensive applications of these compounds. Thus, alternative compounds with similar optoelectronic properties need to be developed. Bismuth possesses electronic structure similar to that of lead with the presence of ns2 electrons that exhibit rich structural variety as well as interesting optical and electronic properties. Herein, we critically assess Cs3Bi2I9 as a candidate for thin-film solar cell absorber. Despite a reasonable optical band gap (∼2 eV) and absorption coefficient, the power conversion efficiency of the Cs3Bi2I9 mesoscopic solar cells was found to be severely lacking, limited by the poor photocurrent density. The efficiency of the Cs3Bi2I9 solar cell can be slightly improved by changing the stoichiometry of the precursor solutions, which is most probably due to the reduction in nonradiative defects as evident from our single-crystal photoluminescence spectroscopy. However, detailed investigations on pristine Cs3Bi2I9 reveal that zero-dimensional molecular crystal structure remains one of the main bottlenecks in achieving high performance. On the basis of our comprehensive studies, we have proposed that a continuous network of three-dimensional crystal structure should be another major criterion in addition to proper band gap and suitable optical properties of the future PV compounds. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

Surface imperfections in perovskite films upon crystallization may trigger trap-assisted non-radiative recombination which is a dominant recombination mechanism that potentially restricts the performance of solar devices. In this work, 2D alkylammonium halide perovskites are formed on the 3D perovskite structure to passivate interfacial defects and vacancies and enhance moisture tolerance. The hybrid 3D/2D perovskite films possess longer photoluminescence lifetimes, as well as lower trap state densities, indicating the passivation of cationic and halide vacancies on the surface or grain boundaries, thereby reducing the non-radiative recombination pathways. More importantly, the hybrid 3D/2D perovskite exhibits higher ambient stability than a pure 3D perovskite where the hydrophobic nature of the long aliphatic carbon chains in the 2D perovskite provide an additional moisture repelling effect to the entire perovskite film. With this approach, the power conversion efficiency of perovskite solar cells was improved from 14.17% to 15.74% along with improved device stability. The hybrid 3D/2D perovskite solar cell retained 86% of its initial power conversion efficiency whereas the control device lost almost 40% of its overall efficiency. Thus, the hybrid 3D/2D perovskite structure is an alternative solution for modulating defects and trap-state densities in high efficiency perovskite solar cells with simultaneously enhanced moisture stability. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

Metal halide perovskites have established themselves as extraordinary optoelectronic materials, exhibiting promise for applications in large area illumination and displays. However, low luminescence, low efficiencies of the light-emitting diodes (LEDs), and complex preparation methods currently limit further progress towards applications. Here, we report on a new and unique mesoscopic film architecture featuring the self-assembly of 3D formamidinium lead bromide (FAPbBr3) nanocrystals of graded size, coupled with microplatelets of octylammonium lead bromide perovskites that enables an energy cascade, yielding very high-performance light-emitting diodes with emission in the green spectral region. These hierarchically structured perovskite films exhibit photoluminescence quantum yields of over 80% and LEDs associated with record high efficiencies in excess of 57.6 cd A−1 with an external quantum efficiency above 13%. Additionally, due to low turn-on voltages (~2.2 V) the LEDs have power efficiencies exceeding 58 lumens per Watt, obtained without any light-outcoupling structures. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

High photoluminescence quantum yields and narrow emission wavelengths, combined with low temperature solution processing, make CH3NH3PbBr3 nanocrystals (NCs) favorable candidates for light-emitting applications. Herein, we describe the synthesis of CH3NH3PbBr3 NC inks by a convenient room-temperature ligand assisted reprecipitation protocol. We further investigate the effect of modulation of CH3NH3Br:PbBr2 ratio during NC synthesis on the optical properties, crystallinity, particle size distribution and film formation of the NC ink. Subsequently, we fabricate LEDs using these NCs as the emissive layer and the highest efficiency (1.75% external quantum efficiency) and brightness (>2700 cd m-2) is achieved for the 1.15:1 precursor ratio. It is inferred that NC surface properties and film coverage are more crucial than photoluminescence intensity to achieve high device efficiency. Moreover, by separating, the NC synthesis and thin film formation processes, we can exert more control during device fabrication, which makes it very promising for scale-up applications. NRF (Natl Research Foundation, S’pore) Accepted version

Inorganic hole-transport layers (HTLs) are widely investigated in perovskite solar cells (PSCs) due to their superior stability compared to the organic HTLs. However, in p–i–n architecture when these inorganic HTLs are deposited before the perovskite, it forms a suboptimal interface quality for the crystallization of perovskite, which reduces device stability, causes recombination, and limits the power conversion efficiency of the device. The incorporation of an appropriate functional group such as sulfur-terminated surface on the HTL can enhance the interface quality due to its interaction with perovskite during the crystallization process. In this work, a bifunctional Al-doped CuS film is wet-deposited as HTL in p–i–n architecture PSC, which besides acting as an HTL also improves the crystallization of perovskite at the interface. Urbach energy and light intensity versus open-circuit voltage characterization suggest the formation of a better-quality interface in the sulfide HTL–perovskite heterojunction. The degradation behavior of the sulfide-HTL-based perovskite devices is studied, where it can be observed that after 2 weeks of storage in a controlled environment, the devices retain close to 95% of their initial efficiency. National Research Foundation (NRF) Accepted version This research was funded by the National Research Foundation, Prime Minister’s Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) program. The authors would like to acknowledge the Facility for Analysis, Characterization, Testing and Simulation, Nanyang Technological University, Singapore, for use of their XPS/UPS facilities. They would also like to thank Dr. Gonzalo Carrasco from Earth Observatory of Singapore, NTU, for his assistance in carrying out ICPMS.

Research into perovskite-based light-emitting diodes (PeLEDs) has been rapidly gaining momentum since the initial reports of green-emitting methylammonium lead bromide (CH3NH3PbBr3)-based devices were published. However, issues pertaining to its stability and morphological control still hamper progress toward high performing devices. Solvent engineering, a technique typically employed to modulate film crystallization, offers little opportunity for scale-up due to the tendency for inhomogeneous film growth and low degree of reproducibility. Here, we propose and show a simple gas-facilitated process to deposit a stable, all-inorganic perovskite CsPbBr3 film. The formation of smaller and less percolated grains, which gives rise to enhanced optical properties, highlights the importance of spatial charge confinement in the film. Consequently, the performance of our PeLEDs shows great improvement, with luminance as high as 8218 cd m–2 and turn-on voltage as low as 2.4 V. Concomitantly, the current efficiency and EQE of our device were increased to 0.72 cd A–1 and 0.088%, respectively. High reproducibility in the performance of PeLEDs fabricated using this process opens the path for large-area devices. NRF (Natl Research Foundation, S’pore) ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Published version

The development of high efficiency semitransparent perovskite solar cells is necessary for application in integrated photovoltaics and tandem solar cells. However, perovskite’s sensitivity to temperature and solvents impose a restriction on following processes, thus favoring physical vapor deposition for the transparent contacts. Protection may be necessary, especially for high energy sputtering and a transparent buffer layer providing good electrode adhesion and conductivity is desired. Here we evaluate Ag and MoOx buffer layers in pursuit of high efficiency tandem solar cells. The usage of thin Ag as a buffer layer demonstrated indium tin oxide (ITO) contacts that were resistant to delamination and yielded a 16.0% efficiency of semitransparent perovskite solar cell with average transparency of 12% in visible range and >50% in near-infrared. Further application in tandem with Cu(In,Ga)Se showed an overall efficiency of 20.7% in a 4-terminal (4T) configuration, exceeding the individual efficiencies of the subcells. NRF (Natl Research Foundation, S’pore) ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Accepted version

Improved light harvesting efficiency can be achieved by enhancing the optical properties of the titanium dioxide (TiO2) photoanode in dye-sensitized solar cells (DSSCs), leading to higher power conversion efficiency. By incorporating submicrometer cavities in TiO2 mesoporous film, using zinc oxide (ZnO) particles as a template, a bimodal pore size structure has been created, called a mesoporous–macroporous nanostructure. This photoanode structure consists of 20-nm TiO2 nanoparticles with two kinds of pores with size of 20 nm (mesopores) and 500 nm (macropores). Energy-dispersive x-ray spectroscopy and x-ray diffraction studies showed no trace of ZnO in the TiO2 after removal by TiCl4 treatment. Higher diffuse transmittance of this film compared with the standard transparent photoanode provides evidence of improved light scattering. When employed in a device, the incident-photon-to-current efficiency of ZnO-assisted devices showed enhancement at longer wavelengths, corresponding to the Mie light scattering effect with the macropores as scattering centers. This resulted in overall higher power conversion efficiency of the DSSC. In this work, a nonvolatile gel ionic liquid was used as the electrolyte to also demonstrate the benefit of this structure in combination with a viscous electrolyte and its promising application to prolong the stability of DSSCs.

Despite their emergence as promising materials for low-cost and efficient energy power generation technology, hybrid organ-ic-inorganic lead-halide perovskites’ instability towards moisture and heat stress remains a serious obstacle that needs to be tackled for commercialization. Here, we show improved moisture and thermal stability through the use of cesium oleate to modify the perovskite/hole transporting material (HTM) interface. Passivation using cesium oleate does not induce the for-mation of any low dimensional perovskites, suggesting that the organic species only passivates the perovskite’s surface and grain boundaries. As a result, enhanced hydrophobic character of perovskite film is realized upon passivation, evidenced by high water contact angle of 107.4 degree and improved stability at ambient condition (relative humidity of ~70%, room tem-perature). Concomitantly, the proposed passivation strategy leads to increased amount of cesium concentration within the films, resulting in beneficial enhanced thermal stability of the film at 85oC. By maintaining the three-dimensional (3D) structure of the solar absorber while concurrently passivating the interfacial defects and vacancies, improved open-circuit voltage (Voc) and unsacrificed short-circuit current density (Jsc) were obtained from the treated devices, leading to power conversion effi-ciencies of over 18%. When stored in a humid environment (relative humidity of ~55%), devices with cesium oleate passivation maintain 88% of its initial PCEs after 720 hours, degrading two times slower than those of the control. This work offers a strat-egy of coating 3D perovskites with unique combination of inorganic cation and long chain organics to provide hydrophobicity and moisture stability to the solar absorber layer, while maintaining good device performances. NRF (Natl Research Foundation, S’pore) Accepted version

Tandem solar cells consisting of perovskite and silicon sub-cells are very promising for low-cost electricity generation due to low fabrication cost and high efficiency potential. Due to the limited active area of perovskite top cells available at the moment, the fabrication of small-area passivated contact n-type monoPolyTM silicon solar cells customized for tandem applications is investigated by scaling down from 6-inch full-size solar cells fabricated using industrial tools. The directly fabricated small-area silicon solar cells have an efficiency of 33% for the wavelength range 750 - 1100 nm of the AM1.5G solar spectrum. By optimizing both perovskite and silicon sub-cells, an energy conversion efficiency of 24.9% was achieved for perovskite on silicon four-terminal tandem cells.

Three-pulse ultrafast spectroscopy reveals interfacial obstacles in methylammonium lead iodide during hot carrier transfer., Halide perovskites are promising materials for development in hot carrier (HC) solar cells, where the excess energy of above-bandgap photons is harvested before being wasted as heat to enhance device efficiency. Presently, HC separation and transfer processes at higher-energy states remain poorly understood. Here, we investigate the excited state dynamics in CH3NH3PbI3 using pump-push-probe spectroscopy. It has its intrinsic advantages for studying these dynamics over conventional transient spectroscopy, albeit complementary to one another. By exploiting the broad excited-state absorption characteristics, our findings reveal the transfer of HCs from these higher-energy states into bathophenanthroline (bphen), an energy selective organic acceptor far above perovskite’s band edges. Complete HC extraction is realized only after overcoming the interfacial barrier formed at the heterojunction, estimated to be between 1.01 and 1.08 eV above bphen’s lowest unoccupied molecular orbital level. The insights gained here are essential for the development of a new class of optoelectronics.

Room-temperature spin-based electronics is the vision of spintronics. Presently, there are few suitable material systems. Herein, we reveal that solution-processed mixed-phase Ruddlesden–Popper perovskite thin-films transcend the challenges of phonon momentum-scattering that limits spin-transfer in conventional semiconductors. This highly disordered system exhibits a remarkable efficient ultrafast funneling of photoexcited spin-polarized excitons from two-dimensional (2D) to three-dimensional (3D) phases at room temperature. We attribute this efficient exciton relaxation pathway towards the lower energy states to originate from the energy transfer mediated by intermediate states. This process bypasses the omnipresent phonon momentum-scattering in typical semiconductors with stringent band dispersion, which causes the loss of spin information during thermalization. Film engineering using graded 2D/3D perovskites allows unidirectional out-of-plane spin-funneling over a thickness of ~600 nm. Our findings reveal an intriguing family of solution-processed perovskites with extraordinary spin-preserving energy transport properties that could reinvigorate the concepts of spin-information transfer., Spin-information transport or transfer is essential for spintronics applications and often relies on high purity and quality materials. Here, the authors report on the defect-tolerant solution-processed Ruddlesden–Popper halide perovskites, where a spin propagation length of 600 nm was achieved via spin funneling.

Recently, semitransparent perovskite solar cells (ST-PSCs) have received overwhelming attention due to their potential applications in building-integrated photovoltaics (BIPV) and in tandem solar cells. The best ST-PSCs, despite the high efficiency achieved, still show limited bifacial properties and lack esthetic properties. Here, we have demonstrated efficient bifacial colorful ST-PSCs using copper thiocyanate (CuSCN), as a hole-transporting material, in an n–i–p architecture. The n–i–p ST-PSCs exhibit the highest reported bifacial factor of 93.7% and achieve a bifacial equivalent efficiency of 22.1% when illuminated under 1 sun standard conditions on the front side and with a reflected albedo of ∼54.4% from the back side. We have also demonstrated that the colorful appearance of CuSCN-based ST-PSCs can be easily tuned across the entire visible spectrum by tuning either the indium tin oxide (ITO) or the CuSCN thickness without affecting their final efficiency. The wide colorful tunability and excellent bifacial photovoltaic behavior of CuSCN-based ST-PSCs make them a promising candidate for BIPV applications. NRF (Natl Research Foundation, S’pore) Accepted version

Tandem solar cells (SCs) based on perovskite and silicon represent an exciting possibility for a breakthrough in photovoltaics, enhancing SC power conversion efficiency (PCE) beyond the single-junction limit while keeping the production cost low. A critical aspect to push the tandem PCE close to its theoretical limit is the development of high-performing semitransparent perovskite top cells, which also allow suitable near-infrared transmission. Here, we have developed highly efficient semitransparent perovskite SCs (PSCs) based on both mesoporous and planar architectures, employing Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3 and FA0.87Cs0.13PbI2Br perovskites with band gaps of 1.58 and 1.72 eV, respectively, which achieved PCEs well above 17 and 14% by detailed control of the deposition methods, thickness, and optical transparency of the interlayers and the semitransparent electrode. By combining our champion 1.58 eV PSCs (PCE of 17.7%) with an industrial-relevant low-cost n-type Si SCs, a four-terminal (4T) tandem efficiency of 25.5% has been achieved. Moreover, for the first time, 4T tandem SCs’ performances have been measured in the low light intensity regime, achieving a PCE of 26.6%, corresponding to revealing a relative improvement above 9% compared to the standard 1 sun illumination condition. These results are very promising for their implementation under field-operating conditions. NRF (Natl Research Foundation, S’pore) Accepted version

Growing a monocrystalline layer of lead halide perovskites directly over substrates is necessary to completely harness their stellar properties in optoelectronic devices, as the single crystals of these materials are extremely brittle. We study the crystallization mechanism of perovskites by antisolvent vapor diffusion to its precursor solution and find that heterogeneous nucleation prevails in the process, with the crystallization dish walls providing the energy to overcome the nucleation barrier. By perturbing the system using sonication, we are able to introduce homogeneously nucleated seed crystals in the precursor solution. These seeds lead to the growth of closely packed crystals over surface-modified substrates kept in the precursor solution. This crystallization process is substrate independent and scalable and can be utilized to fabricate planar optoelectronic devices. We demonstrate a methylammonium lead iodide planar crystal photoconductor with a colossal detectivity of 1.48 × 1013 Jones. NRF (Natl Research Foundation, S’pore) Accepted version

Semitransparent perovskite solar cells (SCs) and their potential integration with silicon SCs in tandem configurations attract significantly increasing interest in the photovoltaics community. In addition to being highly spectrally complementary, these perovskite and silicon SCs have very different optimal‐performing sizes and consequently ideal measurement schemes for their integration in four‐terminal (4T) tandem configurations need to be investigated in detail. Herein, the effect of different active areas on both perovskite and silicon SCs on their photovoltaic performances is investigated. Furthermore, the commonly used filtering 4T tandem measurement scheme (named as filtered) is systematically compared with the size‐matching scheme (named as masked) demonstrating that when using the same top semitransparent perovskite and bottom silicon SCs in different measurements schemes, the total 4T tandem power conversion efficiency (PCE) can differ by more than 1%. The concepts presented here highlight the importance of optimal measurement schemes to assess 4T tandem PCE and rationalize the effect of compromise between the subcells size matching and the identification of the maximum PCE potential. NRF (Natl Research Foundation, S’pore) Accepted version

With the current research impetus on neuromorphic computing hardware, realizing efficient drift and diffusive memristors are considered critical milestones for the implementation of readout layers, selectors, and frameworks in deep learning and reservoir computing networks. Current demonstrations are predominantly limited to oxide insulators with a soft breakdown behavior. While organic ionotronic electrochemical materials offer an attractive alternative, their implementations thus far have been limited to features exploiting ionic drift a.k.a. drift memristor technology. Development of diffusive memristors with organic electrochemical materials is still at an early stage, and modulation of their switching dynamics remains unexplored. Here, halide perovskite (HP) memristive barristors (diodes with variable Schottky barriers) portraying tunable diffusive dynamics and ionic drift are proposed and experimentally demonstrated. An ion permissive poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate interface that promotes diffusive kinetics and an ion source nickel oxide (NiOx) interface that supports drift kinetics are identified to design diffusive and drift memristors, respectively, with methylammonuim lead bromide (CH3NH3PbBr3) as the switching matrix. In line with the recent interest on developing artificial afferent nerves as information channels bridging sensors and artificial neural networks, these HP memristive barristors are fashioned as nociceptive and synaptic emulators for neuromorphic sensory signal computing. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version NRF‐CRP14‐2014‐03 NRF2018‐ITC001‐001 MOE2016‐T2‐1‐100 MOE2018‐T2‐2‐083

Embedding metal nanoparticles in the active layer of organic solar cells has been explored as a route for improving charge carrier generation, with localized field enhancement as a proposed mechanism. However, embedded metal nanoparticles can also act as charge recombination sites. To suppress such recombination, the metal nanoparticles are commonly coated with a thin insulating shell. At the same time, this insulating shell limits the extent that the localized enhanced electric field influences charge generation in the organic medium. It is presumed that there is an optimal thickness which maximizes field enhancement effects while suppressing recombination. Atomic Layer Deposition (ALD) was used to deposit Al2O3 layers of different thicknesses onto silver nanoparticles (Ag NPs), in a thin film of P3HT. Photoinduced absorption (PIA) spectroscopy was used to study the dependence of the photogenerated P3HT(+) polaron population on the Al2O3 thickness. The optimal thickness was found to be 3-5 nm. This knowledge can be further applied in the design of metal nanoparticle-enhanced solar cells.

Monolithic perovskite modules with active areas of 31 cm2 and 70 cm2 and with power conversion efficiencies (PCE) of 10.46% and 10.74%, respectively, were fabricated using scalable printing processes. An ambient stability of more than 2000 h with less than a 5% reduction in efficiency is demonstrated. The electrical quality of the mesoscopic hole transporter and its facilitation of efficient infiltration is paramount. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

This Editorial introduces one of two companion Special Issues on “Halide Perovskites for Optoelectronics Applications” in Energy Technology and ChemSusChem following the ICMAT 2017 Conference in Singapore. More information on the other Special Issue can be found in the Editorial published in ChemSusChem.

This Editorial introduces one of two companion Special Issues on "Halide Perovskites for Optoelectronics Applications" in ChemSusChem and Energy Technology following the ICMAT 2017 Conference in Singapore. More information on the other Special Issue can be found in the Editorial published in Energy Technology.