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The all-inorganic perovskite CsPbI 3 quantum dots are difficult to achieve pure red stable luminescence due to their poor lattice thermodynamic stability and non-radiative recombination loss caused by surface halide vacancies. Therefore, the pure red perovskites are usually achieved by mixing the composition of halides (Br and I). In this work, CsPb(Br/I) 3 quantum dots (QDs) were synthesized by the hot-injection method under the synergistic effect of homophthalic acid (HA), 2-bromoethanesulphonic acid sodium salt (SBES), and oleylamine (OAm). By adjusting the molar ratio of passivates, the synergistic effect of multiple ligands can not only passivate the unliganded Pb2+-related defects on the surface of NCs, but also increase the formation energy of halide vacancies. Meanwhile, due to the bidentate structure of HA, smaller size of perovskites nanocrystals were obtained. Eventually, synergistic boost in device performance is achieved for color-by-blue white light-emitting diodes (WLEDs) with CIE coordinates of (0.3319, 0.3297) and have an external quantum efficiency (EQE) of 10.13%. This strategy paves an efficient way for improving the efficiency and stability of CsPb(Br/I) 3 NCs. • Highly efficient, highly stable and smaller sized CsPb(BrI) 3 perovskite quantum dots are obtained by using homophthalic acid and 2-bromoethanesulphonic acid sodium salt instead of OA for passivation. • CsPb(BrI) 3 perovskite quantum dots exhibit narrow red photoluminescence at 620 nm with excellent quantum yield of 71% • CsPb(BrI) 3 perovskite quantum dots maintain excellent stability at high temperatures (80 °C), high humidity (80% humidity), and after 90 days of storage. • Realize white light-emitting diode with 10.13% external quantum efficiency CIE chromaticity coordinate of (0.3331, 0.3297) and 21.38 lm/W power efficiency. [ABSTRACT FROM AUTHOR]

Abstract: With the rapid progress in developing hybrid perovskite solar cells, the allure of current density–voltage (  J–V) hysteresis has attracted quite a lot of interest in the research community. It requires feasible approaches that further deepen the fundamental understanding of device physics in specific device architecture in order to solve this problem eventually. Here, perovskite solar cells configured with different counter electrodes are systematically investigated with the focus on charge accumulation within the devices responsible for J–V hysteresis. The results indicate that J–V hysteresis is affected by charge accumulation which can be modulated by carrier extraction efficiency of the electrodes. Through a rationally induced interfacial dipole, the devices have shown improvement in carrier extraction, which thus reduces J–V hysteresis significantly. It provides solid evidence for the proposition that interface charge plays an important role in J–V hysteresis, and demonstrates an applicable strategy that effectively alleviates J–V hysteresis in perovskite solar cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • 3-Chloroperoxybenzoic acid (m-CPBA) as a p-dopant is introduced into spiroOMeTAD. • m-CPBA accelerates Spiro oxidation, improves conductivity, reduces defects. • m-CPBA adjusts HOMO, tune energy array match, reduces energy loss at interface. • m-CPBA optimized PSCs achieves an efficiency of 23.34% with fill factor of 84.24%. The perovskite solar cells (PSCs) is one of the fastest growing photovoltaic technology. However, the further improvement of performance and stability is the bottleneck issue of its large-scale manufacturing. The controllable oxidation of spiroOMeTAD is significant for high-performance PSCs. Here, a low-cost and facile strategy by doping 3-Chloroperoxybenzoic acid (m-CPBA) into spiroOMeTAD is demonstrated. The addition of m-CPBA accelerates the oxidation of spiroOMeTAD, produces more carriers, improves the hole conductivity, and reduces defects and carrier non-radiative recombination. On the other hand, the modification of m-CPBA adjusts the HOMO of hole transport layer (HTL), makes more match the energy array between HTL and perovskite layer, and reduces energy loss at interface. Consequently, the m-CPBA optimized PSCs achieves a power conversion efficiency (PCE) of 23.34% with an outstanding fill factor (FF) over 84%, along with excellent environmental stability. [ABSTRACT FROM AUTHOR]

The pursuit of efficient and durable bifunctional electrocatalysts for overall water splitting in acidic media is highly desirable, albeit challenging. SrIrO3 based perovskites are electrochemically active for oxygen evolution reaction (OER), however, their inert activities toward hydrogen evolution reaction (HER) severely restrict the practical implementation in overall water splitting. Herein, an Ir@SrIrO3 heterojunction is newly developed by a partial exsolution approach, ensuring strong metal‐support interaction for OER and HER. Notably, the Ir@SrIrO3‐175 electrocatalyst, prepared by annealing SrIrO3 in 5% H2 atmosphere at 175 °C, delivers ultralow overpotentials of 229 mV at 10 mA cm−2 for OER and 28 mV at 10 mA cm−2 for HER, surpassing most recently reported bifunctional electrocatalysts. Moreover, the water electrolyzer using the Ir@SrIrO3‐175 bifunctional electrocatalyst demonstrates the potential application prospect with high electrochemical performance and excellent durability in acidic environment. Theoretical calculations unveil that constructing Ir@SrIrO3 heterojunction regulates interfacial electronic redistribution, ultimately enabling low energy barriers for both OER and HER. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cumene hydroperoxide (CHP) is introduced to improve the property of spiro-OMeTAD. • CHP doping causes the conductivity increase and trap-state density decline of HTL. • The doped PSC obtains an efficiency of 20.33%, and the undoped device gets 18.00%. Hole transport layer is one of the primary factors that improve the optical-electric properties of perovskite solar cells. Spiro-OMeTAD is frequently utilized as hole transport materials in PSCs. However, pristine or oxygen oxidized spiro-OMeTAD has low mobility and conductivity. Herein, cumene hydroperoxide is introduced to accelerate the oxidation of spiro-OMeTAD, which improves the carrier mobility, declines the trap-state density and optimizes the energy match with perovskite layer, leading to the enhancement of the performance of device. Kelvin probe force microscopy images and Atomic force microscopy images show the improvement of interface morphology. Multiple electrochemical characterizations demonstrate the acceleration of spiro-OMeTAD oxidation, the enhancement of conductivity of the doped hole transport material, and the decline of trap-state density and carrier annihilation in hole transport layer/perovskite interface after the modification. The perovskite solar cell doped with optimal concentration acquires a power conversion efficiency of 20.33%, while the undoped device gets an efficiency of 18.00%. [ABSTRACT FROM AUTHOR]

Defects formed at the surface, buried interface and grain boundaries (GB) of CsPbI 3 perovskite films considerably limit photovoltaic performance. Such defects could be passivated effectively by the most prevalent post modification strategy without compromising the photoelectric properties of perovskite films, but it is still a great challenge to make this strategy comprehensive to different defects spatially distributed throughout the films. Herein, a spatially selective defect management (SSDM) strategy is developed to roundly passivate various defects at different locations within the perovskite film by a facile one-step treatment procedure using a piperazine-1,4-diium tetrafluoroborate (PZD(BF 4) 2) solution. The small-size PZD2+ cations could penetrate into the film interior and even make it all the way to the buried interface of CsPbI 3 perovskite films, while the BF 4 − anions, with largely different properties from I− anions, mainly anchor on the film surface. Consequently, virtually all the defects at the surface, buried interface and grain boundaries of CsPbI 3 perovskite films are effectively healed, leading to significantly improved film quality, enhanced phase stability, optimized energy level alignment and promoted carrier transport. With these films, the fabricated CsPbI 3 PSCs based on carbon electrode (C-PSCs) achieve an efficiency of 18.27%, which is among the highest-reported values for inorganic C-PSCs, and stability of 500 h at 85 °C with 65% efficiency maintenance. [ABSTRACT FROM AUTHOR]

CsPbI3 perovskite is a promising light absorber in perovskite solar cells (PSCs) due to its suitable bandgap (Eg) and high chemical stability, but the perovskite phase is metastable in ambient atmosphere and prone to defect formation. To enhance phase stability and reduce defects, forming a low dimensional (LD) perovskite on CsPbI3 has proved effective. However, the energy levels for most of low‐conductivity LD perovskites are not very compatible with those of CsPbI3, which will impair charge separation and device performance. Herein, a new 1D perovskite (5‐Azaspiro[4.4]nonan‐5‐ium lead triiodide, ASNPbI3) with compatible energy levels and a large Eg is reported as a capping layer. The p‐type ASNPbI3 forms a p‐n heterojunction with n‐CsPbI3 with a staggered band alignment, considerably enhancing the carrier separation. Besides, by pre‐forming a ASNPbI3 at an intermediate stage, defects are suppressed in perovskite film. Consequently, the CsPbI3 PSCs based on carbon electrode without hole transporter (C‐PSCs) achieves a PCE of 18.34%, which is among the highest‐reported values for inorganic C‐PSCs. Furthermore, the hydrophobic ASNPbI3 capping layer has a high thermal stability that greatly enhances perovskite phase stability. Hence, the CsPbI3 C‐PSCs maintains 68% of its initial PCE after 400 h aging at 85°C in a N2 glovebox. [ABSTRACT FROM AUTHOR]

The efficiency of perovskite solar cells (PSCs) is hindered by substantial defects within the grain boundaries (GBs) of polycrystalline perovskite films. Conventional post‐treatment strategies struggle to precisely repair these defects at GBs. Here, a targeted grain boundary passivation strategy through solvent effects by incorporating symmetrical biphenyl molecules is proposed, 4,4′‐diaminodiphenyl sulfone (DDS) and 4,4′‐sulfodiphenol (SDP), aiming to mitigate defects at GBs and optimize energy level arrangements through their electric dipole effects. Compared to the pristine device, the SDP‐modified device exhibits significant improvements, including a champion efficiency of 24.39% and an impressive fill factor, along with excellent operation stability. This work provides an effective and straightforward solution for improving the performance of PSCs. [ABSTRACT FROM AUTHOR]

Eu3+- or Sm3+-doped Sr 2 GaNbO 6 perovskite phosphors are synthesized by a high-temperature solid-phase method, and their luminescence performance, energy transfer, and thermal sensitivity are studied. The results showed that Sr 2 GaNbO 6 phosphor is an effective self-activated host, and successful doping with rare-earth ions is proven by their characteristic emission. At 332-nm excitation, both the broadband emissions from s-orbital mixing of the transition metal ions Nb5+ and Sr2+ and GaO 6 groups and the sharp emissions from Eu3+ or Sm3+ ions are observed for Sr 2 GaNbO 6 :R3+ (R = Eu, Sm) phosphors, respectively. The emission color can be modulated from blue to white by regulating the doping concentration of Eu3+ or Sm3+, which is attributed to the effective energy transfer from s-orbital mixing of the transition metal ions Nb5+ and Sr2+ and GaO 6 groups to Eu3+ or Sm3+. Based on the emission fluorescence intensity ratio of the s-orbital mixing of the transition metal ions Nb5+ and Sr2+ and GaO 6 groups to the Eu3+ or Sm3+ ions in the range of 298–623 K, optical temperature sensing properties of Sr 2 GaNbO 6 :R3+ showed the maximum absolute and relative sensitivities are 0.0193 K−1 and 1.86% K−1 at 298 K of Sr 2 GaNbO 6 :0.018Eu3+ phosphor, respectively, as well as 0.00862 K–1 and 1.70% K−1 at 298 K and at 623 K, respectively, of Sr 2 GaNbO 6 :0.08Sm3+ phosphor. These results demonstrate a viable strategy to tune the emitting color and achieve optical temperature sensing in single-doped phosphors by controlling the energy transfer between the self-activated host and the activator. This strategy provides application potential for the white light-emitting diodes and non-contact thermometric multifunctional materials. • The crystal structure and luminescence properties of self-activated Sr 2 GaNbO 6 perovskite host have been investigated. • Color-tunable properties of Sr 2 GaNbO 6 perovskite phosphors can be obtained by doping of Eu3+ or Sm3+ ions. • Eu3+ or Sm3+-doped Sr 2 GaNbO 6 perovskite phosphors are promising temperature-sensing materials with high performance. [ABSTRACT FROM AUTHOR]

Including an ultrathin insulator interlayer at the perovskite/charge transport interface is a critical strategy for suppressing surface recombination in state‐of‐the‐art perovskite solar cells. However, its further improvement with increased thickness faces a trade‐off due to the exponentially inhibited electrical transport. Here, a patterned insulator contact (PIC) design is presented to overcome this passivation‐transport trade‐off where the conventional ultrathin interlayer is replaced by a thicker counterpart with local openings. Such a PIC is realized using metal fluorides with a high coverage of 80% and a thickness tolerance increased by 3–5. Balancing inhibited transport via local openings is verified by direct observation with local photocurrent mapping. It revealed the atomic passivation mechanism of hydrogen bonding between fluoride ions and perovskite organic cations. It extends the top‐surface passivation to double‐sided passivation and find that LiF‐modified substrate improves the wettability and promotes the out‐of‐plane growth of perovskite. These combined advances and distilled knowledge allow us to achieve power‐conversion‐efficiency (PCE) of 25% (certified 24.95%) in p–i–n perovskite solar cells by simultaneously enhancing the open‐circuit voltage (Voc) and the fill factor (FF). The device's reproducibility and operational stability are also improved. [ABSTRACT FROM AUTHOR]

Due to its enormous development potential, research on perovskite solar cells (PSCs) is progressing rapidly worldwide. Among numerous hole transport materials (HTMs), an organic molecule spiro-OMeTAD emerged victorious. Spiro's application in PSCs is constrained to its weak hole mobility and low conductivity. Here, an inexpensive, ecologically friendly inorganic oxidant iodine pentoxide (I 2 O 5) is used to aid in quick and manageable oxidation of Spiro. I 2 O 5 -modified Spiro as HTM improves the charge carrier transportation. Meanwhile, trap-states density and trap-assisted recombination are decreased. Additionally, the modification adjusts the HTM's energy level to match the perovskite layer properly. As a result, the I 2 O 5 -modified PSC achieves a champion power conversion efficiency of 22.80%, while the pristine device gets an efficiency of 20.65%. [Display omitted] • Iodine pentoxide (I 2 O 5) is introduced to spiro-OMeTAD hole transport layer. • I 2 O 5 -introduction adjusts Spiro oxidation rate and increase carrier concentration. • I 2 O 5 -modification decreases defect density and trap-assisted recombination. • I 2 O 5 -treated PSC achieves an efficiency of 22.80%, pristine device gets 20.65%. [ABSTRACT FROM AUTHOR]

Organic‐inorganic hybrid perovskites are promising candidates for direct X‐ray detection and imaging. The relatively high dark current in perovskite single crystals (SCs) is a major limiting factor hindering the pursuit of performance and stability enhancement. In this study, the contribution of dark current is disentangled from electronic (σe) and ionic conductivity (σi) and shows that the high σi dominates the dark current of MAPbBr3 SCs. A multilayer heterojunctions passivation strategy is developed that suppresses not only the σi by two orders of magnitude but also σe by a factor of 1.6. The multilayer heterojunctions passivate the halide vacancy defects and increase the electron and hole injection barrier by inducing surface p‐type doping of MAPbBr3. This enables the MAPbBr3 SC X‐ray detectors to obtain a high sensitivity of 19 370 µC Gyair−1 cm−2 under a high electric field of 100 V cm−1, a record high sensitivity for bromine self‐powered devices, and a low detection limit of 42.3 nGyair s−1. The unencapsulated detectors demonstrate a stable baseline after storage for 210 days and outstanding operational stability upon irradiation with an accumulated dose of up to 1944 mGyair. [ABSTRACT FROM AUTHOR]

Highlights: The gelation of hole transport layer generates a dense and uniform hole transport layer film and significantly inhibits the aggregation of lithium bis(trifluoromethane sulfonyl)imide in spiro-OMeTAD. The gelated hole transport layer confers enhanced charge carrier transport and better humidity and operational stability of perovskite solar cells. To achieve high power conversion efficiency (PCE) and long-term stability of perovskite solar cells (PSCs), a hole transport layer (HTL) with persistently high conductivity, good moisture/oxygen barrier ability, and adequate passivation capability is important. To achieve enough conductivity and effective hole extraction, spiro-OMeTAD, one of the most frequently used HTL in optoelectronic devices, often needs chemical doping with a lithium compound (LiTFSI). However, the lithium salt dopant induces crystallization and has a negative impact on the performance and lifetime of the device due to its hygroscopic nature. Here, we provide an easy method for creating a gel by mixing a natural small molecule additive (thioctic acid, TA) with spiro-OMeTAD. We discover that gelation effectively improves the compactness of resultant HTL and prevents moisture and oxygen infiltration. Moreover, the gelation of HTL improves not only the conductivity of spiro-OMeTAD, but also the operational robustness of the devices in the atmospheric environment. In addition, TA passivates the perovskite defects and facilitates the charge transfer from the perovskite layer to HTL. As a consequence, the optimized PSCs based on the gelated HTL exhibit an improved PCE (22.52%) with excellent device stability. [ABSTRACT FROM AUTHOR]

Electronic doping is applied to tailor the electrical and optoelectronic properties of semiconductors, which have been widely adopted in information and clean energy technologies, like integrated circuit fabrication and PVs. Though this concept has prevailed in conventional PVs, it has achieved limited success in the new-generation PV materials, particularly in halide perovskites, owing to their soft lattice nature and self-compensation by intrinsic defects. In this review, we summarize the evolution of the theoretical understanding and strategies of electronic doping from Si-based photovoltaics to thin-film technologies, e.g., GaAs, CdTe and Cu(In,Ga)Se2, and also cover the emerging PVs including halide perovskites and organic solar cells. We focus on the chemical approaches to electronic doping, emphasizing various chemical interactions/bonding throughout materials synthesis/modification to device fabrication/operation. Furthermore, we propose new classifications and models of electronic doping based on the physical and chemical properties of dopants, in the context of solid-state chemistry, which inspires further development of optoelectronics based on perovskites and other hybrid materials. Finally, we outline the effects of electronic doping in semiconducting materials and highlight the challenges that need to be overcome for reliable and controllable doping. [ABSTRACT FROM AUTHOR]

Sensitive and stable X‐ray detectors are essential for medical diagnostics, nondestructive industrial inspection, and security inspection. Halide perovskite X‐ray detectors are promising for direct X‐ray detection because of their high sensitivity and low limit of detection (LoD). However, their high and unstable dark current, caused by notorious ion migration in hybrid perovskites, limits their performance and long‐term operation stability. Moreover, it is still challenging to prepare high‐quality perovskite with millimeter‐thickness at a large‐scale. In this paper, solid–liquid transition of two‐dimensional (2D) Ruddlesden‐Popper (RP) perovskites enabled by methylamine gas (CH3NH2) is first reported. Based on this novel approach, dense RP perovskite films with tunable ion migration and superior electronic features are produced using a lamination process. The tradeoff between stability and detection performance of perovskite X‐ray detectors is successfully solved by tuning the quantum well width of RP perovskites. X‐ray detectors with a sensitivity of 5362.3 µC Gyair−1 cm−2, LoD of 8.1 nGyair s−1 and highly working stability are achieved simultaneously. Furthermore, single gamma photon detection is realized in the RP perovskite detectors, which further confirms their capability for detecting radiation at ultralow dose rates. This study paves the way for adopting polycrystalline RP perovskites in stable X‐ray detectors. [ABSTRACT FROM AUTHOR]

The electrical properties of the perovskite oxide thermoelectric material SrTiO 3 (STO) should be improved in order to realize its thermoelectric application due to its intrinsic insulation characteristics. The bulk STO materials usually optimize their electrical properties by annealing in reducing environment after synthesis. However, this method inevitably leads to the gradient distribution of oxygen defect concentration in materials. In this study, the combination of High Temperature and High Pressure (HPHT) method is used, and Ti powder is added to optimize the electrical properties of STO materials. HPHT provides a closed synthesis environment. In addition, with the strong oxygen-capturing ability of Ti at high temperature, the semi-conductivity of materials is performed. The thermoelectric properties of the synthesized materials under HPHT are studied using XRD, XPS, SEM, and TEM. The properties and micro-morphology of the synthesized samples with different Ti contents are investigated. The results show that, with the increase of the Ti content, the oxygen defect concentration increases and the electrical properties are significantly improved. Simultaneously, the sample synthesized using the HPHT method changes its micro-morphology and reduces the thermal conductivity of the material. The increase of oxygen vacancy concentration can also effectively reduce the thermal conductivity. Under the collaborative optimization of HPHT while adding Ti, the maximum obtained zT value at 20 wt% addition is 0.19 @ 973 K. The density functional theory calculation also shows that, compared with pure STO, the band gap of STO with oxygen vacancy decreases, which increases the conductivity. Therefore, a high pressure and the addition of Ti powder provide a fast, simple and efficient method for preparing oxygen-deficient perovskite oxide materials, which is of great significance for improving its thermoelectric properties. • The introduction of oxygen vacancies effectively improves the electrical properties. • High pressure-induced micromorphological changes and generated oxygen vacancies reduce thermal conductivity. • The whole synthesis procedure last only for 30 min • Theoretical calculations show that oxygen vacancies can significantly improve the electrothermal transport properties of perovskite-structured materials. [ABSTRACT FROM AUTHOR]

• The surface composition of perovskite films are affected by spin coat speed. • The quality of perovskite film grown at relatively low spin coat speeds is better. • The superior device performance can be obtained at relatively low spin coat speeds. Recently, 2D perovskite has emerged as a promising alternative material for solar cell applications because of its superior stability in wet environments. Among the various methods for preparing 2D perovskite films, spin coat is the most widely used due to its low pollution, high accuracy and energy efficiency. In this study, the effects of spin coat speed on the surface morphology, crystal structure and surface composition of 2D perovskite (BA 2 MA 3 Pb 4 I 13) films are investigated using X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy and other techniques. It is found that the BA 2 MA 3 Pb 4 I 13 film has large crystal size, good crystallinity and small lattice constant at a relatively low spin coat speeds. The device performance test showed that the BA 2 MA 3 Pb 4 I 13 film can obtain better device performance as well. It indicated that the photovoltaic performance of perovskite solar cells can be significantly improved by optimization of the fabrication parameters during the film preparation process. [ABSTRACT FROM AUTHOR]

The tandem cell structure is the most promising solution for the next generation photovoltaic technology to overcome the single‐junction Shockley–Queisser limit. The fabrication of a perovskite/c‐Si monolithic tandem device has not yet been demonstrated on a c‐Si bottom cell produced from an industrial production line. Here, a c‐Si cell with a tunneling oxide passivating contact (TOPCon) structure produced on a production line as the bottom cell of a tandem device, and a top cell featuring solution‐processed perovskite films to form the tandem device are used. The c‐Si cell features a rough damage etched, but untextured front surface from the wafering processes. To combat the challenge of rough surfaces, several strategies to avoid shunt paths across carrier transport layers, absorber layers, and their interfaces are implemented. Moreover, the origin of reflection loss on this planar structure is investigated and the reflection loss is managed to below 4 mA cm−2. In addition, the source of the voltage loss from the TOPCon bottom cell is identified and the device structure is redesigned to be suitable for tandem applications while still using mass production feasible fabrication methods. Overall, 27.6% efficiency is achieved for a monolithic perovskite/c‐Si tandem device, with significant potential for future improvements. [ABSTRACT FROM AUTHOR]

Formamidinium (FA)‐based lead triiodide have emerged as promising light‐harvesting materials for solar cells due to their intriguing optoelectronic properties. However, obstacles to commercialization remain regarding the primary intrinsic materials instability, wherein volatile organic components of FA+ cations are prone to escape under operational stressors. Herein, stabilizing FA‐based perovskite through toughening the interface with the symmetric molecule of 1,1′‐(Methylenedi‐4,1‐phenylene) bismaleimide (BMI) is reported. BMI with two maleimides can simultaneously bind with FA+ and/or undercoordinated Pb2+ through chemical bonding, which also compresses the resultant perovskite lattice. The chemical bonding and strain modulation synergistically not only passivate film defects, but also inhibit perovskite decomposition, thus significantly improving the intrinsic stability of perovskite films. As a result, the BMI‐modified perovskite solar cells (PSCs) show improved power conversion efficiency (PCE) from 21.4% to 22.7% and enhanced long‐term operational stability, maintaining 91.8% of the initial efficiency after 1000 h under continuous maximum power point tracking. The findings shed light on the synergetic effects of chemical interactions and physical regulations, which opens a new avenue for stable and efficient perovskite‐based optoelectronic devices. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) have become a promising candidate for the next‐generation photovoltaic technologies. As an essential element for high‐efficiency PSCs however, the heavy metal Pb is soluble in water, causing a serious threat to the environment and human health. Due to the weak ionic bonding in three‐dimensional (3D) perovskites, drastic structure decomposition occurs when immersing the perovskite film in water, which accelerates the Pb leakage. By introducing the chemically stable Dion‐Jacobson (DJ) 2D perovskite at the 3D perovskite surface, the film dissolution is significantly slowed down, which retards lead leakage. As a result, the Pb contamination is dramatically reduced under various extreme conditions. In addition, the PSCs device deliver a power conversion efficiency (PCE) of 23.6 % and retain over 95 % of their initial PCE after the maximum power point tracking for over 1100 h. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) have become a promising candidate for the next‐generation photovoltaic technologies. As an essential element for high‐efficiency PSCs however, the heavy metal Pb is soluble in water, causing a serious threat to the environment and human health. Due to the weak ionic bonding in three‐dimensional (3D) perovskites, drastic structure decomposition occurs when immersing the perovskite film in water, which accelerates the Pb leakage. By introducing the chemically stable Dion‐Jacobson (DJ) 2D perovskite at the 3D perovskite surface, the film dissolution is significantly slowed down, which retards lead leakage. As a result, the Pb contamination is dramatically reduced under various extreme conditions. In addition, the PSCs device deliver a power conversion efficiency (PCE) of 23.6 % and retain over 95 % of their initial PCE after the maximum power point tracking for over 1100 h. [ABSTRACT FROM AUTHOR]

Special attention should be devoted to the thermal stability of hybrid perovskite solar cells (PSCs), because they are often operated at elevated temperatures. However, effective strategies are lacking for manipulation of heat flow in PSCs to improve their thermal stability. Here, a holistic solution is reported for the rapid removal of dissipated heat within the absorber by introducing hexagonal boron nitride (h‐BN) inside and radiator fin outside of the device. This strategy significantly improves the thermal conductivity of perovskite and speeds up the heat transfer of device, which effectively reduces the cell temperature under illumination of simulated AM 1.5G standard spectrum by ≈6.5 °C. Regardless of device configurations, the corresponding PSCs exhibit prolonged lifetimes aged at different temperatures, continuously operated under white light‐emitting diode (LED) lamp or full‐spectrum illumination. Of particular note, the optimized h‐BN/Cu device with n–i–p structure keeps 88% and 93% of its initial PCE after 1776 h of 85 °C thermal aging and 2451 h of maximum power point (MPP) tracking, respectively, and the device with p–i–n structure maintains 96% and 92% of its original PCE after 1704 h of 85 °C thermal aging and 2164 h of MPP tracking. [ABSTRACT FROM AUTHOR]

[Display omitted] The practical applications of perovskite solar cells (PSCs) are limited by the further improvement of their stability and performance. Interface engineering is a promising strategy to solve these pain points. Herein, we design (R)-(-)-1-cyclohexylethylamine iodide (R-CEAI), composed of positively charged hydrophobic R-CEA+ and negatively charged I–, to post-treat the interface of 3D mixed-cation/halide perovskite with assist one of isopropyl alcohol (IPA). R-CEAI treatment not only passivates the defects at surface and grain boundaries of perovskite, but also in-situ grows quasi 2D Ruddlesden-Popper perovskite at the interface between 3D perovskite and hole transport layer, which reduces trap density of states, tunes energy level and alleviates lattice distortion. As a result, R-CEAI treated 2D/3D PSCs yield a champion PCE of 22.52%, with an improved open-circuit voltage of 1.195 V and retain 84.34% of their initial efficiency in long-term stability test, while the pristine device provides a PCE of 19.43% with only 54.30% retention. [ABSTRACT FROM AUTHOR]

Wesuccessfully demonstrated an integrated perovskite/bulk-heterojunction(BHJ) photovoltaic device for efficient light harvesting and energyconversion. Our device efficiently integrated two photovoltaic layers,namely a perovskite film and organic BHJ film, into the device. Thedevice structure is ITO/TiO2/perovskite/BHJ/MoO3/Ag. A wide bandgap small molecule DOR3T-TBDT was used as donor inthe BHJ film, and a power conversion efficiency (PCE) of 14.3% wasachieved in the integrated device with a high short circuit currentdensity (JSC) of 21.2 mA cm–2. The higher JSCas compared to thatof the traditional perovskite/HTL (hole transporting layer) device(19.3 mA cm–2) indicates that the BHJ film absorbslight and contributes to the current density of the device. Our resultfurther suggests that the HTL in traditional perovskite solar cell,even with good light absorption capability, cannot contribute to theoverall device photocurrent, unless this HTL becomes a BHJ layer (byadding electron transporting material like PC71BM). [ABSTRACT FROM AUTHOR]

[Display omitted] • Formamidine acetate (FAAc) additive is introduced to TiO 2 /perovskite interface. • FAAc passivates interface defect, tunes energy array and improve crystal quality. • FAAc-modified device achieves an efficiency of 20.47%, along with ease hysteresis. • While the pristine perovskite solar cell obtains an efficiency of 18.30%. Perovskite solar cells (PSCs) have received widespread attention due to their excellent photovoltaic characteristics. However, the nonradiative recombination of carriers induced by defects limits the stability and performance of PSCs. Interface and additive engineering are good medicine to cure the disease. Herein, formamidine acetate (FAAc) as interfacial additive is introduced to the TiO 2 /perovskite interface. The connection of the FA+ between the TiO 2 and perovskite promotes electron transport, and the amino group (−NH 2) and carboxyl group (−COOH) of FAAc passivates the defect at TiO 2 /perovskite interface. Meanwhile, the FAAc modification tunes the energy array and improves crystal quality of perovskite. In consequence, the PSC based on FAAc-modified TiO 2 achieves the best power conversion efficiency (PCE) of 20.47%, accompanied with excellent stability and mitigated hysteresis, while PCE of the pristine PSC is 18.30%. [ABSTRACT FROM AUTHOR]

The 2D/3D composite structure possesses both the excellent stability of 2D perovskite and the excellent performance of 3D perovskite, which recently have attracted special attention. Different from the popular isopropanol, a novel additive solvent—polypropylene glycol bis (2‐aminopropyl ether) (A‐PPG) is introduced here to dissolve excess PbI2 and perovskite, and then reconstruct and in situ form the quasi‐2D perovskite layer on 3D perovskite bulk. The lone electron pairs of the ether‐oxygen and amino in A‐PPG can form coordination bonds with Pb2+. The introduction of A‐PPG tunes the energy array of functional layers, passivates defects, and mitigates carrier nonradiative recombination. Consequently, the 2D/3D perovskite device exhibits a championship efficiency of 22.24% with a distinguished open‐circuit voltage of 1.21 V (the thermodynamic limit of 1.30 V). Moreover, the 2D/3D device still maintains 90% of the original efficiency in the ambient atmosphere with a relative humidity of 30 ± 10% after 50 days. [ABSTRACT FROM AUTHOR]

Lead halide perovskites with excellent optoelectronic properties have attracted extensive attention and made amazing progress for X-ray detectors and imaging. However, lead is highly toxic to humans, animals and ecosystems, posing a great safety concern to its commercial application. It has become an urgent need to develop stable and environment-friendly lead-free alternatives. In this review, we summarize recent progress in lead-free halide perovskites (LFHPs) and derivatives toward X-ray detectors and imaging. First, we introduce the working principle of X-ray detectors and the key figure of merit in direct and indirect detection processes. In addition, we summarize state-of-the-art lead-free halide perovskites preparation methods. Furthermore, we comprehensively discuss the structural dimensions, optoelectronic properties of lead-free halide perovskites and their recent advances in X-ray detection and imaging. Meanwhile, the stabilities of LFHPs-based X-ray detectors are discussed. Finally, we outline several main issues of state-of-the-art LFHPs-based X-ray detectors and provide prospects to overcome these limitations. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) have rapidly developed in recent years with the advantages of high efficiency and low cost. Although PSCs are the fastest-advancing solar technology to date, bottlenecks such as J–V hysteresis have limited the further development significantly. In this work, we have investigated the in-depth mechanism of hysteresis in both three-dimensional (3D) and quasi-2D (Q-2D) planar p-i-n PSCs. We conducted scanning-rate-dependent and temperature-dependent measurements to distinguish the ion migration and the capacitive charging. The coefficient for capacitance and pseudocapacitance from the J–V curves are further employed to analysis the hysteresis. It is found that both capacitance and ion migration contribute to the J–V hysteresis, but play different roles in 3D and Q-2D perovskite devices. In 3D PSCs, the ion migration has substantial impacts on the J–V hysteresis, wherein ions are tending to move. While in the Q-2D PSCs, the capacitance extends the characteristic charging time, which is mainly responsible for J–V hysteresis. These findings will help to effectively suppress the hysteresis for 3D and Q-2D PSCs, eventually benefiting device performance and long term stability. [ABSTRACT FROM AUTHOR]

Summary of main observation and conclusion: The heterojunction‐type structure has shown significant merits in tuning the optical properties and carrier physics. Inspired by the excellent absorption capability of halide perovskite materials for visible light, a series of CsPbBr3/TiO2 heterojunction‐type photocatalysts with various all‐inorganic‐perovskite/TiO2 ratios are successfully fabricated by the ligand‐assisted reprecipitation (LARP) method. The heterojunction structure extends the light absorption of TiO2 with good chemical and structural stability. A Pb‐O interaction at the CsPbBr3/TiO2 interface is observed by the XPS and confirmed by the TRPL showing improved interface carrier transport and stability. The heterojunction‐type catalyst shows drastically enhanced photocatalytic activity towards the direct oxidation of toluene with O2 molecule, as an important reaction for organic chemical synthesis. The optimized sample shows an activity of 2356 μmol·g–1·h–1 at 75 °C, 4 times of that of the naked CsPbBr3 nanocrystals, and 3 times of that of the bare TiO2. Based on the investigation with trapping agents, a reaction mechanism is hence proposed suggesting that the photo‐generated hole may be involved in the rate‐limiting step. This work demonstrates the potential of inorganic halide perovskite‐based heterojunction structure for photocatalytic applications. [ABSTRACT FROM AUTHOR]

The defects in perovskite films are one of the most non‐negligible factors that can attenuate the performances of perovskite solar cell. This work fabricates defect‐reduced perovskite film by using the lead indicator (dithizone) as an additive of perovskite functional layer. The dithizone can retard the crystallization rate of perovskite films, passivate the defects, and enhance the structure stability of perovskite by coordinating with lead atoms. As a result, the device doped with dithizone yields outstanding power conversion efficiency and stability. [ABSTRACT FROM AUTHOR]

The defects in perovskite films are one of the most non‐negligible factors that can attenuate the performances of perovskite solar cell. This work fabricates defect‐reduced perovskite film by using the lead indicator (dithizone) as an additive of perovskite functional layer. The dithizone can retard the crystallization rate of perovskite films, passivate the defects, and enhance the structure stability of perovskite by coordinating with lead atoms. As a result, the device doped with dithizone yields outstanding power conversion efficiency and stability. [ABSTRACT FROM AUTHOR]

Organic ammonium cations play a vital role in building structures and tuning energy bands of organic–inorganic halide perovskites and the consequent photoelectric characteristics. Here, two 2D lead bromide perovskites: flat‐layered (BDA)PbBr4 (BDA = 1, 4‐butanediammonium), corrugation‐layered (PDA)7Pb6Br26 (PDA = 1, 3‐propanediammonium) and a 1D nanobelt‐shaped (EDA)2PbBr6 (EDA = ethylenediammonium) are built to explore their tunable structure, energy bands, and photoluminescence by a series of linear alkyl diammonium cations. Significant "spatial effect" of diammonium cations directly controls the space configurations of these lead bromide perovskites. From 2D (100)‐flat to 1D (110)‐nanobelt, distortions and disconnections of lead bromide layers are beneficial to the quantum confinement and generation of self‐trapping exciton (STE) energy levels of low‐dimensional perovskites. Upon ultraviolet excitation, (BDA)PbBr4, (PDA)7Pb6Br26, and (EDA)2PbBr6 exhibit blue, broadband yellowish white, and "warm" white emissions, respectively. Density functional theory combining STE theory demonstrates their bandgap changes and emission mechanisms. This work provides a basis for tuning the structure of low‐dimensional organic–inorganic halide perovskites for better photochromic properties. [ABSTRACT FROM AUTHOR]

Lead halide perovskites with mixed cations/anions often suffer from phase segregation, which is detrimental to device efficiency and their long‐term stability. During perovskite film growth, the gel stage (in between liquid and crystalline) correlates to phase segregation, which has been rarely explored. Herein, cation diffusion kinetics are systematically investigated at the gel stage to develop a diffusion model obeying Fick's second law. Taking 2D layered perovskite as an example, theoretical and experimental results reveal the impact of diffusion coefficient, temperature, and gel duration on the film growth and phase formation. A homogenous 2D perovskite thin film was then fabricated without significant phase segregation. This in‐depth understanding of gel stage and relevant cation diffusion kinetics would further guide the design and processing of halide perovskites with mixed composition to meet requirements for optoelectronic applications. [ABSTRACT FROM AUTHOR]

Lead halide perovskites with mixed cations/anions often suffer from phase segregation, which is detrimental to device efficiency and their long‐term stability. During perovskite film growth, the gel stage (in between liquid and crystalline) correlates to phase segregation, which has been rarely explored. Herein, cation diffusion kinetics are systematically investigated at the gel stage to develop a diffusion model obeying Fick's second law. Taking 2D layered perovskite as an example, theoretical and experimental results reveal the impact of diffusion coefficient, temperature, and gel duration on the film growth and phase formation. A homogenous 2D perovskite thin film was then fabricated without significant phase segregation. This in‐depth understanding of gel stage and relevant cation diffusion kinetics would further guide the design and processing of halide perovskites with mixed composition to meet requirements for optoelectronic applications. [ABSTRACT FROM AUTHOR]

ABX3‐type halide perovskite nanocrystals (NCs) have been a hot topic recently due to their fascinating optoelectronic properties. It has been demonstrated that A‐site ions have an impact on their photophysical and chemical properties, such as the optical band gap and chemical stability. The pursuit of halide perovskite materials with diverse A‐site species would deepen the understanding of the structure–property relationship of the perovskite family. In this work we have attempted to synthesize rubidium‐based perovskite NCs. We have discovered that the partial substitution of Rb+ by Cs+ help to stabilize the orthorhombic RbPbBr3 NCs at low temperature, which otherwise can only be obtained at high temperature. The inclusion of Cs+ into the RbPbBr3 lattice results in highly photoluminescent Rb1−xCsxPbBr3 NCs. With increasing amounts of Cs+, the band gaps of the Rb1−xCsxPbBr3 NCs decrease, leading to a redshift of the photoluminescence peak. Also, the Rb1−xCsxPbBr3 NCs (x=0.4) show good stability under ambient conditions. This work demonstrates the high structural flexibility and tunability of halide perovskite materials through an A‐site cation substitution strategy and sheds light on the optimization of perovskite materials for application in high‐performance optoelectronic devices. Adding stability: Lead halide perovskite nanocrystals (NCs) attract tremendous attention due to their extraordinary optical properties. Herein, we show that the partial substitution of Rb+ by Cs+ helps to stabilize the orthorhombic RbPbBr3 NCs at low temperature, which otherwise could only be obtained at high temperature (above 300 °C, see figure). [ABSTRACT FROM AUTHOR]

The components with soft nature in the metal halide perovskite absorber usually generate lead (Pb)0 and iodine (I)0 defects during device fabrication and operation. These defects serve as not only recombination centers to deteriorate device efficiency but also degradation initiators to hamper device lifetimes. We show that the europium ion pair Eu3+-Eu2+ acts as the “redox shuttle” that selectively oxidized Pb0 and reduced I0 defects simultaneously in a cyclical transition. The resultant device achieves a power conversion efficiency (PCE) of 21.52% (certified 20.52%) with substantially improved long-term durability. The devices retained 92% and 89% of the peak PCE under 1-sun continuous illumination or heating at 85°C for 1500 hours and 91% of the original stable PCE after maximum power point tracking for 500 hours, respectively. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we report a sequential twice anti-solvent deposition (STAD) method for the preparation of high performance perovskite solar cells. In comparison with the traditional one-step anti-solvent processing method, this STAD method improves the perovskite thin film quality and consequently improves the device performance. For the CH 3 NH 3 PbI 3-x Cl x cell, the highest power conversion efficiency (PCE) improved from 14.20% for the traditional cells to 15.70% for the STAD cells, corresponding to a 10% performance enhancement. PCE enhancement of around 5% was also found both for MAPbI 3-x Br x and MAPbI 3 cells, demonstrating the generality for the performance enhancement for the STAD process. In addition, operational stability of the perovskite cells fabricated by the STAD process was also found to be enhanced than the traditional one-step cells. Scanning electronic microscope (SEM) and atomic force microscope (AFM) analyses confirm that smaller perovskite crystal domains as well as smoother surface morphology for the perovskite films prepared by the STAD method. A mechanism was proposed as that perovskite nano crystals formed at the first deposition-annealing process step serves as the crystalline seeds for the crystal growth in the second deposition-annealing process, which leads to more homogeneous crystal growth and to a consequent smooth and condense perovskite film. The current work provides a feasible method to prepare high quality perovskite solar cells with higher device performance as well as device stability. Graphical abstract In this work, a sequential twice anti-solvent deposition method was developed for the deposition of perovskite solar cells, which was found to be able to improve the crystal quality of the perovskite thin film, and consequently improve device performance and stability. Image 1 Highlights • A sequential twice anti-solvent deposition process for perovskite film is reported. • Smoother and more condense perovskite crystals were found for the STAD process. • Both device performance and stability are improved for the STAD method. [ABSTRACT FROM AUTHOR]

We systematically investigated the impact of stoichiometric ratio variation between PbX2 and AX on hybrid perovskite films from the perspective of microstructure, especially on the plane stacking directions, using the two-dimensional synchrotron radiation grazing incidence wide-angle X-ray scattering (GIWAXS) technique. The tuned crystal plane stacking in perovskite films can consequently enlighten further explorations about the relationship between microstructure and solar cell performance. [ABSTRACT FROM AUTHOR]

The halide perovskite (PVSK) materials (with ABX3 formulation) have emerged as 'dream materials' for photovoltaic (PV) applications due to their remarkable physical properties such as high optical absorption coefficient, carrier mobility, long carrier diffusion lengths, etc. These properties have enabled the PV devices to reach higher than 20% power conversion efficiencies (PCE) in record time. The further pursuit of higher PCE and improved stability brings forth increasing interests in so-called 'mixed composition' PVSK materials, consisting of partial substitution of the A, B, and/or X-sites with alternative elements/molecules of similar size. Herein, we highlight the recent advances in developing mixed PVSK for PVs and their relevant optoelectronic properties. We mainly focus on mixed PVSK materials in the form of polycrystalline thin films, but also discuss nanostructured and two-dimensional (2D) PVSK materials due to the increasing interest of broad readership. Efforts are exerted to elucidate the design principles of mixed PVSK and fabrication techniques for high performance optoelectronic devices, which help deepen our fundamental understanding of mixed PVSK systems. We hope this review will shed light onto the design and synthesis of mixed PVSK materials to further the progress of PVSK photovoltaics towards higher efficiencies and longer lifetimes. [ABSTRACT FROM AUTHOR]

The design of electron transport layers (ETLs) is crucial to the performance of optoelectronic devices. A composite ETL was constructed to overcome the poor carrier extraction issue in perovskite solar cells, resulting in a maximum PCE of 19.14% with reduced hysteresis. A similar enhancement phenomenon was observed in both devices based on TiO2 and SnO2 ETLs. [ABSTRACT FROM AUTHOR]

A simple chemical process was developed in a scalable manner, to reduce trap states in perovskite absorbers from the very beginning. The obvious decrease of I2 in methylammonium iodide and the decrease of trap density in the resultant films were identified, which led to the power conversion efficiency (PCE) of perovskite solar cells (PSCs) increase from 16.5% to 18.5%. [ABSTRACT FROM AUTHOR]

• It is reported to a method that loads NPs on MXene. • MX-TiO 2 as an ETL can improve interface contact and release lattice strain. • The carbon-based CsPbI 2 Br PSC achieves a high PCE of 15.48 %, and that of the 1cm2 one also has 13.06 %. • This strategy can be applied to the CsPbI x Br 3-x system perovskites. Poor interfacial contact and residual stress in perovskite solar cells (PSC) are known to reduce device stability and photoelectric performance. Herein, a novel strategy was developed by embedding TiO 2 NPs into CH 3 COO− (AC−)-functionalized MXene (MX, Ti 3 C 2) as an electron transport layer (ETL). The strong interaction between the AC− of MX and Pb2+ of perovskite reinforces the interfacial contact between the ETL and perovskite layer, releasing harmful lattice strain. Meanwhile, charge accumulation and non-radiative carrier recombination at the interface were effectively suppressed. As a result, the carbon-based CsPbI 2 Br PSC achieved a champion efficiency of 15.48 %, and the large-area (≥1 cm2) device also demonstrated high efficiency (13.06 %). The CsPbIBr 2 and CsPbI 3 counterparts yielded high efficiencies of 11.22 % and 14.59 %, respectively. Moreover, the devices showed excellent environmental stability, maintaining 91 % of original efficiency after being stored in air at a relative humidity of about 20–30 % for 1250 h. It also retained 85 % of its original efficiency when stored at 85 °C in a nitrogen atmosphere for > 400 h. [ABSTRACT FROM AUTHOR]

[Display omitted] • 1,8-Naphthyridine (1,8-ND) as a modifier is implanted at the interface of PVK/HTL. • 1,8-ND reconstructs perovskite to fabricate efficient α-FAPbI 3 phase and 2D/3D PSCs. • 1,8-ND coordinate with Pb2+ to passivate defects and construct quasi-2D perovskite. • 1,8-ND modified 2D/3D PSC achieved a champion PCE of 23.8% with excellent stability. The ionic properties of components determine that perovskite films will generate numerous charged surface defect under continuous high-temperature annealing, resulting in suboptimal performance and poor stability of perovskite solar cells (PSCs). Based on the principle of Lewis acid-base coordination, 1,8-naphthyridine (1,8-ND) with electron-rich structure was used to form complexes with Pb2+ ions, and high-quality 2D/3D perovskite films with effective defect passivation were prepared by surface modification. Benefiting from suppressed nonradiative recombination, extended carrier lifetime, modified charge transport, improved hydrophobic properties and the optimized phase stability of α-FAPbI 3 , 1,8-ND modified 2D/3D PSCs with negligible hysteresis and satisfactory stability achieved a champion power conversion efficiency of 23.8% whose open circuit voltage was significantly improved from 1.09 V to 1.15 V, providing a resultful strategy to passivate surface defect while constructing 2D/3D perovskite. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lansoprazole (Lanz), as a Four-functional additive is introduced perovskite layer. • Modification of Lanz tunes energy match and improves perovskite crystal quality. • Hydrophobic and electron-donor groups on Lanz raise stability and passivate defects. • Lanz-modified device obtains an efficiency of 24.05%, along with excellent stability. The practical applications of organic–inorganic hybrid metal halide-based perovskite solar cells (PSCs), as the fastest growing photovoltaic devices, are limited by the further improvement of their stability and performance. Additive engineering is considered as a hopeful strategy to alleviate these issues. Herein, Lansoprazole (Lanz), as a multifunctional additive, has four effects for ameliorating the stability and performance of PSCs. The strong hydrophobic trifluoromethyl group on Lanz can cover atop of perovskite to build a moisture-oxygen-barrier; The high electron-donating sulfinyl moiety on Lanz can provide lone electron pair to lead ions to passivate defects; The modification of Lanz can adjust Fermi-level of perovskite and optimize the energy match of functional layers; The introduction of Lanz can moderate the growth rate of perovskite, improve crystal quality and reduce grain boundaries and defects. Consequently, the Lanz-modified device achieves an excellent PCE of 24.05% compared to the pristine device (PCE of 21.91%). Meanwhile the modified device possesses excellent environmental and operational stability that maintains 84% of its initial PCE under continuous irradiation for 500 h. [ABSTRACT FROM AUTHOR]

In planar heterojunction (PHJ) perovskite solar cells (PerSCs) without mesoporous metal oxide skeleton, there is challenge of formation perovskite film with full coverage to the conductive substrate through solution-process the lead halide precursors. Selecting a lead source with more volatile byproducts is an effective approach to obtain much smoother films with smaller and fewer pinholes. Herein, we demonstrate efficient CH 3 NH 3 PbI 3 /PCBM PHJ PerSCs by using lead acetate (Pb(Ac) 2 ) as lead precursor. The morphology of the perovskite thin films were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively, and the crystalline quality of the perovskite films were investigated by X-ray diffraction (XRD) spectroscopy. Time-resolved photoluminescence (TRPL) was used to investigate the PL lifetime of the perovskite film. The perovskite film derived from Pb(Ac) 2 shows enhanced surface coverage and improved photoluminescence lifetime in comparison with PbI 2 sourced perovskite film. Averaged over 20 individual devices, the power conversion efficiency (PCE) of devices derived from Pb(Ac) 2 reaches 14.81%, much higher than PbI 2 sourced devices by one-step (8.23%) or two-step (10.58%) spin-coating. [ABSTRACT FROM AUTHOR]

[Display omitted] • MoO 3 dope PTAA to lower its HOMO aligning better with MAPbI 3 VBM. • The hole transport and the interfacial hole extraction are enhanced. • The fabricated inverted planar PSCs achieve a champion PCE of 20.06%. The hole transport layer (HTL) plays a key role in determining the performance of planar perovskite solar cells (PSCs). Poly[bis(4-phenyl)(2,4, 6-triMethylphenyl)aMine] (PTAA), a polymer with good stability, is one of the promising HTL candidates for PSCs. However, notable interfacial carrier recombination limits the performance of PSCs based on PTAA HTL, due to the large gap between the highest-occupied molecular orbital (HOMO) of PTAA and the valance band maximum (VBM) of MAPbI 3 perovskite as well as the low intrinsic hole mobility of PTAA. Herein, PTAA was doped by 3 wt% of molybdenum oxide (MoO 3) to move down its HOMO by 0.16 eV, leading to a better matching with the MAPbI 3 perovskite. Meanwhile, the MoO 3 dopant was demonstrated to improve the hole transport in PTAA and hole extraction at the PTAA/perovskite interface. Eventually, the fabricated inverted planar PSCs using PTAA HTL with 3 wt% MoO 3 achieved the PCE of 20.06% as compared to that of 17.71% by using pristine PTAA HTL. The present work thus proposes a simple approach to utilize MoO 3 as a dopant to substantially improve the molecular HTLs for high-performance PSCs and other perovskite-based optoelectronics. [ABSTRACT FROM AUTHOR]

The structure, thermodynamic and elastic properties of magnesium silicate (MgSiO) post-perovskite at high pressure are investigated with quasi-harmonic Debye model and ab initio method based on the density functional theory (DFT). The calculated structural parameters of MgSiO post-perovskite are consistent with the available experimental results and the recent theoretical results. The Debye temperature, heat capacity and thermal expansion coefficient at high pressures and temperatures are predicted using the quasi-harmonic Debye model. The elastic constants are calculated using stress-strain relations. A complete elastic tensor of MgSiO post-perovskite is determined in the wide pressure range. The calculated elastic anisotropic factors and directional bulk modulus show that MgSiO post-perovskite possesses high elastic anisotropy. [ABSTRACT FROM AUTHOR]

Hole transport materials (HTMs) play an important role in perovskite solar cells (PSCs). At present, the most frequent used HTM is spiro-OMeTAD. However, spiro-OMeTAD without dopants have low electrical conductivity and hole mobility. Therefore, the improvement of mobility and conductivity of hole transport layer (HTL) has become a crucial issue. Here, we introduce a dopant, thionyl chloride (SOCl 2), to oxidize spiro-OMeTAD and generate more spiro-OMeTAD+. Under the same conditions, the optimized device doped with SOCl 2 achieves a power conversion efficiency (PCE) of 20.76%, while the pristine one is only 18.13%. The doping of SOCl 2 not only reduces the density of defect states at the interface between perovskite and HTL, but also suppresses the recombination of light-induced carriers. In addition, the stability of the PSCs based on SOCl 2 is greatly improved, which can maintain 90% of the initial PCE for 31 days under ambient conditions. This work provides a simple and feasible strategy for dopant engineering of HTL to achieve efficient PSCs. Image 1 • Thionyl chloride (SOCl 2) is doped to oxidize spiro-OMeTAD and form spiro-OMeTAD+. • The doping reduces the density of defect and the recombination of carriers. • The device doped with SOCl 2 achieves a PCE of 20.76% and excellent stability. • Conversely, the pristine device obtains an efficiency of 18.13%. [ABSTRACT FROM AUTHOR]

Herein, Eu-doped CaSrNb 2 O 7 perovskites are synthesized by using the high-temperature solid-phase method, resulting in layered perovskite structure, with the space group of Cmc 2 1 and a strong luminescence response under excitation wavelength of 314 nm. Moreover, these as-prepared CaSrNb 2 O 7 :xEu3+ (x = 0–0.15) phosphors are color-tunable. Specifically, the color changes from white to blue with raising temperature. After thermal stability testing, the fluorescence intensity ratio, maximum absolute and relative sensor sensitivity of CaSrNb 2 O 7 :xEu3+ are calculated to evaluate the thermal properties of materials. It turned out that the maximum absolute and relative sensor sensitivity are 0.043 K-1 and 0.0105 K-1, and the temperature resolution is as low as 0.0286K, respectively. It suggests that the high sensitivity and excellent resolution of CaSrNb 2 O 7 :xEu3+ make it a promising candidate for optical thermometers. • The CaSrNb 2 O 7 :Eu3+ phosphor has potential in w-LEDs and optical thermometers. • The CaSrNb 2 O 7 luminous color can be tuned to white by adjusting Eu3+ contents. • Based on FIR, CaSrNb 2 O 7 :Eu3+ was a promising optical thermometer. [ABSTRACT FROM AUTHOR]

Organic spacer cations in layered 2D (A1)2(A2)n−1BnX3n+1 (where A1 is an organic cation acting as a spacer between the perovskite layers, A2 is a monovalent cation, e.g., Cs+,CH3NH3+, CH(NH2)2+) perovskite materials improve the long‐term stability of the resulting solar cells, but hamper their power conversion efficiency due to poor carrier generation/transportation. Rational guidelines are thus required to enable the design of organic spacer cations. Herein, mixed A1 cations are employed in layered 2D perovskites to investigate the interplay between alkylamine cations and unsaturated alkylamine cations. It is revealed that alkylamine spacer cations are able to facilitate precursor assembly, which results in the orientated growth of perovskite crystals. Unsaturated alkylamine cations further lead to reduced exciton binding energy, which improves carrier pathway in the 2D perovskites. By mixing both cations, substantially improved open circuit voltage is observed in the resultant photovoltaic cells with the efficiency of 15.46%, one of the highest one based on (A1)2(A2)3Pb4I13 layered 2D perovskites. The generality of the design principle is further extended to other cation combinations. [ABSTRACT FROM AUTHOR]