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The rapid development of non-fullerene acceptors (NFAs) with strong near-infrared absorption has led to remarkably enhanced short-circuit current density (Jsc) values in organic solar cells (OSCs). NFAs based on the benzotriazole (Bz) fused-ring π-core have great potential in delivering both high Jsc and decent open-circuit voltage values due to their strong intramolecular charge transfer with reasonably low energy loss. In this work, we have designed and synthesized a series of Bz-based NFAs, PN6SBO-4F, AN6SBO-4F and EHN6SEH-4F, via regiospecific N-alkyl engineering based on the high-performance NFA mBzS-4F that was reported previously. The molecular packing of mBzS-4F, AN6SBO-4F, and EHN6SEH-4F single crystals was analyzed using X-ray crystallography in order to provide a comprehensive understanding of the correlation between the molecular structure, the charge-transporting properties, and the solar cell performance. Compared with the typical honeycomb single-crystal structure of Y6 derivatives, these NFAs exhibit distinctly different molecular packing patterns. The strong interactions of terminal indanone groups in mBzS-4F and the J-aggregate-like packing in EHN6SEH-4F lead to the formation of ordered 3D networks in single-crystals with channels for efficient charge transport. Consequently, OSCs based on mBzS-4F and EHN6SEH-4F show efficient photon-to-current conversions, achieving the highest power conversion efficiency of 17.48% with a Jsc of 28.83 mA cm−2.

ConspectusOrganic photovoltaics (OPVs) with a photoactive layer containing a blend of organic donor and acceptor species are considered to be a promising technology for clean energy owing to their unique flexible form factor and good solution processability that can potentially address the scalability challenges. The delicate designs of both donors and acceptors have significantly enhanced the power conversion efficiency of OPVs to more than 18%. Nonfullerene small-molecule acceptors (NFAs) have played a critical role in enhancing the short-circuit current density (JSC) by efficiently harvesting near-infrared (NIR) sunlight. To take full advantage of the abundant NIR photons, the optical band gap of NFAs should be further reduced to improve the performance of OPVs. Incorporating highly polarizable selenium atoms onto the backbone of organic conjugated materials has been proven to be an effective way to decrease their optical band gap. For example, a selenium-substituted NFA recently developed by our group has attained a JSC of approximate 27.5 mA cm-2 in OPV devices, surpassing those of most emerging photovoltaic systems. Inspired by this advance, we concentrate on the topic of selenium-containing materials in this Account to incite readers' interest in further exploring this series of materials.In this Account, we first compare the differences among chalcogen heterocycles and discuss the influence of fundamental electronic behavior on the collective photoelectrical properties of the resulting materials. The superior features of selenium-substituted materials are summarized as follows: (1) The large covalent radius of selenium can diminish the π-orbital overlap, rendering enhanced quinoidal resonance character and a narrowed optical band gap of resulting materials. (2) The selenium atom is more polarizable than sulfur owing to its larger and looser outermost electron cloud, enabling enhanced intermolecular Se-Se interaction and increased charge carrier mobility of relevant materials in the solid state. We then focus on summarizing the design rules for various categories of selenium-containing materials including polymer donors, small-molecule acceptors, and polymer acceptors, especially those composed of ladder-type polycyclic units. The motivation for incorporating selenium atoms into these materials and the structure-property relationships were thoroughly elucidated. Specifically, we discuss the changes in the optical band gap, charge carrier mobility, and molecular packing induced by selenium substitution and correlate the effects of these changes with the exciton behaviors, energy loss, and nanoscale film morphology of corresponding OPV devices. Furthermore, we point out the intrinsic stability of selenium-containing materials under maximum-power-point tracking and long-term photo- or thermostress and indicate their potential use in semitransparent and tandem solar cells. At the end, the prospect of future research focuses and the possible applications of selenium-containing materials in the OPV field are discussed.

Summary Interfacial engineering has been commonly used as an effective strategy to enhance device performance and stability of perovskite solar cells (PSCs). However, most of the materials used for interface engineering are based on organics, which may have concerns for the device's long-term stability. Therefore, we developed robust fluoro-terminated TiO2 nanosheets (F-TiO2 NSs) to work as interlayers between perovskite and electron-transporting layers in inverted PSCs. The flat NS morphology of F-TiO2 NSs enables close contact with perovskite with abundant surface fluoro groups, which can interact with undercoordinated lead and MA/FA ions to prevent the formation of cation vacancies and alleviate surface defects. As a result, a remarkable power conversion efficiency (PCE) of 22.86% can be achieved. The operational stability of devices with F-TiO2 NSs interlayers is also enhanced, which can maintain over 90% of their initial PCEs after being monitored at the maximum power point (MPP) for 1,000 h under day/night cycles.

Due to their low-temperature deposition, high mobility (>10 cm2/V·s), and electrical conductivity, amorphous ionic oxide semiconductors (AIOSs) have received much attention for their applications in flexible and/or organic electro-optical devices. Here, we report on a study of the flexibility of CdO-In2O3 alloy thin films, deposited on a polyethylene terephthalate (PET) substrate by radio frequency magnetron sputtering at room temperature. Cd1-xInxO1+δ alloys with the composition of x > 0.6 are amorphous, exhibiting a high electron mobility of 40-50 cm2/V·s, a low resistivity of ∼3 × 10-4 Ω·cm, and high transmittance over a wide spectral window of 350 to >1600 nm. The flexibility of both crystalline and amorphous Cd1-xInxO1+δ films on the PET substrate was investigated by measuring their electrical resistivity after both compressive and tensile bending with a range of bending radii and repeated bending cycles. Under both compressive and tensile bending with Rb = 16.5 mm, no significant degradation was observed for both the crystalline and amorphous films up to 300 bending cycles. For a smaller bending radius, the amorphous film shows much less electrical degradation than the crystalline films under compressive bending due to less film delamination at the bending sites. On the other hand, for a small bending radius ( 90%. The OSCs fabricated on an amorphous Cd1-xInxO1+δ-coated flexible PET substrate achieve a promising PCE of 12.06%. Our results strongly suggest the technological potentials of amorphous Cd1-xInxO1+δ as a reliable and effective transparent conducting material for flexible and organic optoelectronic devices.

All-polymer solar cells (all-PSCs) have achieved tremendous progress due to the recent advances of polymerized small molecule acceptors (PSMAs) and their power conversion efficiencies (PCEs) have reached over 14%. However, the practical applications of all-PSCs are still severely restricted by the lack of PSMAs with a broad absorption spectrum, high electron mobility, low energy loss, and good batch-to-batch reproducibility. Herein, a multi-selenophene-containing PSMA, namely PFY-3Se, based on a selenophene-fused SMA framework and a selenophene π-spacer was designed and developed. Compared to its thiophene analog PFY-0Se, PFY-3Se possesses a significantly red-shifted absorption (~30 nm), increased electron mobility, and improved intermolecular aggregation and packing. When matched with polymer donor PBDB-T, the PFY-3Se-based all-PSCs achieved an impressive PCE of 15.1% with both high short-circuit current density of 23.6 mA cm-2 and high fill factor of 0.737, and a low energy loss, which are among the best values in all-PSCs field reported so far and much better than those of thiophene analogs (PCE=13.0%). More importantly, PFY-3Se maintains similarly good batch-to-batch properties which is very helpful for realizing reproducible device performance. This is the first reported and also is very rare for the PSMAs so far which provides a potential candidate for efficient all-PSCs toward practical applications.

Tuning molecular aggregation via structure design to manipulate the film morphology still remains as a challenge for polymer solar cells based on unfused non-fullerene acceptors (UF-NFAs). Herein, a strategy was developed to modulate the aggregation patterns of UF-NFAs by systematically varying the π-bridge (D) unit and central core (A') unit in A-D-A'-D-A framework (A and D refer to electron-withdrawing and electron-donating moieties, respectively). Specifically, the quantified contents of H- or J-aggregation and crystallite disorder of three UF-NFAs (BDIC2F, BCIC2F, and TCIC2F) were analyzed via UV/Vis spectrometry and grazing incidence X-ray scattering. The results showed that the H-aggregate-dominated BCIC2F with less crystallite disorder exhibited a more favorable blend morphology with polymer donor PBDB-T (poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene)-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5-c']dithiophene-4,8-dione)]) relative the other two UF-NFAs, resulting in improved exciton dissociation and charge tranport. Consequently, photovoltaic devices based on BCIC2F delivered a promising power conversion efficiency of 12.4 % with an exceptionally high short-circuit current density of 22.1 mA cm-2 .

Currently, the performance improvement for inverted perovskite solar cells (PVSCs) is mainly limited by the high open circuit voltage (VOC ) loss caused by detrimental non-radiative recombination (NRR) processes. Herein, we report a simple and efficient way to simultaneously reduce the NRR processes inside perovskites and at the interface by rationally designing a new pyridine-based polymer hole-transporting material (HTM), PPY2, which exhibits suitable energy levels with perovskites, high hole mobility, effective passivation of the uncoordinated Pb2+ and iodide defects, as well as the capability of promoting the formation of high-quality polycrystalline perovskite films. In absence of any dopants, the inverted PVSCs using PPY2 as the HTM deliver an encouraging PCE up to 22.41 % with a small VOC loss (0.40 V), among the best device performances for inverted PVSCs reported so far. Furthermore, PPY2-based unencapsulated devices show an excellent long-term photostability, and over 97 % of its initial PCE can be maintained after one sun constant illumination for 500 h.

All-inorganic perovskite solar cells (PVSCs) have attracted intensive attention owing to their tunable bandgaps and excellent photo- and thermostability, making them promising absorbers in tandem solar cells (TSCs). Herein, we develop an all-inorganic perovskite/organic TSC with a wide bandgap all-inorganic perovskite CsPbI2.1Br0.9 and a narrow bandgap organic photoactive layer (PM6:Y6) serving as top and bottom sub cells respectively. The fabricated tandem solar cell demonstrated a remarkable PCE of 18.06%, with an open-circuit voltage (VOC) of 1.89 V, short-circuit current (JSC) of 12.77 mA cm−2, and fill factor (FF) of 74.81%, which is higher than that of both single junction PVSCs (14.43%) and organic solar cells (14.01%). Moreover, benefiting from the outstanding UV and thermal stability of inorganic perovskites, all-inorganic perovskite-based tandem devices showed superior stability under light and heat, with negligible degradation after 150 h of UV irradiation, 250 h under one sun illumination and 100 h of heating at 80 °C. This work demonstrates that all-inorganic perovskites are an appropriate candidate for the fabrication of efficient and stable TSCs.

Nonfullerene acceptors (NFAs) have played an important role in the development of organic solar cells. However, the optical absorption of most NFAs is limited within 600–900 nm, prohibiting further...

Summary All-small-molecule organic solar cells (SM-OSCs) with a high power conversion efficiency (PCE) of 15.88% (certified 15.5%) are demonstrated by employing 4TIC as the additional non-fullerene acceptor (NFA) to construct ternary SM-OSCs. 4TIC is a highly crystalline acceptor with a similar molecular structure as 6TIC, the host NFA in the binary blend. The addition of 4TIC not only significantly enhances the crystallinity of the blend film but also maintains the desired face-on orientation in the proper multi-length scale morphology to improve both charge extraction and recombination in devices. As a result, the PCE of the ZnP-TBO: 6TIC-based SM-OSCs increases from 12.11% to 14.73% after the addition of 4TIC. For ZnP-TSEH: 6TIC-based SM-OSCs, the PCE increases from 13.54% to 15.88% (certified 15.5%) after the addition of 4TIC. The 15.88% efficiency is the best result for SM-OSCs reported to date.

Despite the notable progress in perovskite solar cells, maintaining long-term operational stability and minimizing potentially leaked lead (Pb2+) ions are two challenges that are yet to be resolved. Here we address these issues using a thiol-functionalized 2D conjugated metal–organic framework as an electron-extraction layer at the perovskite/cathode interface. The resultant devices exhibit high power conversion efficiency (22.02%) along with a substantially improved long-term operational stability. The perovskite solar cell modified with a metal–organic framework could retain more than 90% of its initial efficiency under accelerated testing conditions, that is continuous light irradiation at maximum power point tracking for 1,000 h at 85 °C. More importantly, the functionalized metal–organic framework could capture most of the Pb2+ leaked from the degraded perovskite solar cells by forming water-insoluble solids. Therefore, this method that simultaneously tackles the operational stability and lead contamination issues in perovskite solar cells could greatly improve the feasibility of large-scale deployment of perovskite photovoltaic technology. Two-dimensional conjugated metal–organic frameworks used as an electron-extraction layer enable the realization of highly stable perovskite solar cells with minimized lead ion leakage.

It is widely known that the miscibility between donor and acceptor is a crucial factor that affects the morphology and thus device performance of nonfullerene organic solar cells (OSCs). In this Letter, we show that incorporating a third component with lower miscibility and higher lowest unoccupied molecular orbital (LUMO) level into the state-of-the-art PM6:Y6 system can significantly enhance the performance of devices. The best results of the ternary devices are achieved by adding a small molecular acceptor named ITCPTC (similar to 5% w/w), which significantly improves the power conversion efficiency (PCE) of the host system from 16.44% to 17.42%. The higher LUMO of the third component increases the open-circuit voltage (V-oc), while the low miscibility enlarges the domains and leads to improved short-circuit current density (J(sc)) and fill factor (FF). The efficacy of this strategy is supported by using other nonfullerene third components including an asymmetric small molecule (N7IT) and a polymer acceptor (PF2-DTC), which play the same role as ITCPTC and boost the PCEs to 16.96% and 17.04%, respectively. Our approach can be potentially applied to a wide range of OSC material systems and should facilitate the development of the OSC field.

We have successfully demonstrated the effect of a thin organic bulk-heterojunction (BHJ) interlayer on improving the photovoltaic performance of lead sulfide (PbS) colloidal quantum dot (CQD) solar...

The visual aesthetic that involves color, brightness, and glossiness is of great importance for building integrated photovoltaics. Semitransparent organic solar cells (ST-OSCs) are thus considered as the most promising candidate due to their superiority in transparency and efficiency. However, the realization of high color purity with narrow bandpass transmitted light usually causes the severely suppressed transparency in ST-OSCs. Herein, we present a spectrally selective electrode (SSE) by imitating the integrating strategy of beetle cuticle for achieving narrow bandpass ST-OSCs with high efficiency and long-term stability. The proposed SSE allows for efficient light-selective passage, leading to tunable narrow bandpass transmitted light from violet to red. An optimized power conversion efficiency of 15.07% is achieved for colorful ST-OSCs, which exhibit color purity close to 100% and a peak transmittance approaching 30%. Long-term stability is also improved for ST-OSCs made with this SSE due to the light-rejecting and the moisture-blocking abilities. The realization of bright and colorful ST-OSCs also indicates the application potential of SSEs in light-emitting diodes, lasers, and photodetectors.

Organic nonlinear optical (NLO) materials are very important for high-speed information processing in addressing the challenges of reduced energy consumption and enhanced speed and bandwidth. In particular, organic second-order NLO materials are very promising for meeting the combined requirements of ultra-low energy and ultra-high bandwidth in electro-optic (EO) modulation, while organic third-order NLO materials have good potential for applications in ultra-speed all-optical signal processing (AOSP). This review highlights the recent significant progress made in organic second- and third-order NLO materials. For second-order NLO materials, the recent advances in the efficient and cost-effective synthesis of dipolar polyene chromophores and thin-film engineering for efficient electric field poling are summarized. The applications and prospects of these high-performance EO materials are also discussed. For third-order NLO materials, we discuss the molecular design strategies of cyanine dyes for AOSP applications, particularly focusing on anionic tricyanofuran (TCF)-based cyanines. We aim to provide a better understanding of the structure–property relationships for cyanine-based AOSP materials. Finally, a summary and outlook for advancing high-performance organic NLO materials are provided.

An efficient post-functionalization protocol of the Mitsunobu reaction between a commercial reactive polymer of poly(4-vinylphenol) (PVP) and 9-(2-hydroxylethyl)-N,N,N,N-tetrakis(4-methoxyphenyl)-9H-carbazole-2,7-diamine is reported to synthesize a novel side-chain polymer (PVP-CZ) with a high density of hole transporting moieties. The polymer PVP-CZ exhibits adequate solvent resistance and excellent film forming ability for the fabrication of inverted perovskite solar cells (PVSCs). The thermal, optical and electrochemical properties of PVP-CZ were investigated in detail. The steady-state photoluminescence (PL) and time resolved photoluminescence (TRPL) decay showed the excellent hole-extracting ability of dopant-free PVP-CZ from the perovskite layer. As a result, the inverted PVSCs delivered a respectable power conversion efficiency of 17.75% with a high fill factor of 81.07%. These results indicate that the synthetic strategy using the post-functionalization of the Mitsunobu reaction is a promising protocol to develop novel side-chain hole transporting polymers for highly efficient PVSCs.

Both monoanionic dicarbene pincer chelate and dianionic azole-pyridine-carbazole cyclometalate were successfully employed in the preparation of respective bis-tridentate Ir(III) metal complexes (Cz6–9) in moderate yields. Tuning of emission to blue was achieved by the addition of dual methoxy substituents at the carbazole cyclometalate, as well as the introduction of either methoxy or dimethylamino group at the central pyridinyl fragment of the azole-pyridine-carbazole cyclometalate. Single-crystal X-ray diffraction study was conducted on complex Cz6 in an attempt to provide an unambiguous structural proof. Photophysical properties were next measured in degassed CH2Cl2 solution at RT, giving structureless emission with peak maximum spanning 460–508 nm and photoluminescence quantum yield of 22–87%. A TD-DFT calculation confirmed the dominance of azole-pyridine-carbazole cyclometalate in controlling the emission energy gap, while the carbene pincer was less influential on the detected emission peak wavelength, i.e. acted as an ancillary. Importantly, the experimentally detected radiative lifetime (e.g. 2.78–17.18 μs) showed a clear correlation to the calculated metal-to-ligand charge transfer percentage of the electronic transitions (10.8–7.5%). Organic light-emitting diode devices gave turn-on voltages of 4.3 and 4.3 V, maximum EQE = 16.3 and 12.2%, power efficiencies of 17.6 and 10.4 lm W−1 and with CIEx,y coordinates of (0.16, 0.26) and (0.16, 0.20) for Cz6 and 7 at 15 wt%, confirming their potential as blue dopants for phosphorescent organic light-emitting diodes.

Fused-ring electron acceptor (FREA) based ternary organic solar cells (OSCs) have made significant progress and attracted considerable attention due to their simple device architecture and broad absorption range in devices. There are three key parameters that need to be fine-tuned in ternary OSCs including absorption, energy level and morphology in order to realize high efficiencies. Herein, a series of FREAs with diverse electron-rich cores or electron-deficient terminals are developed and rationally combined to achieve high performance ternary OSCs. The dipole moment of FREAs’ terminals has been unveiled as an important factor and its working mechanism has been thoroughly investigated by systematically studying six ternary OSCs. These ternary blends all exhibit complementary absorption and cascade energy levels, which can facilitate efficient light-harvesting and charge transfer. Additionally, the morphological effects on ternary OSCs are eliminated through comparative studies while demonstrating distinctively different performance. The preliminary results show that compatible dipole moment between two FREAs is critical in ternary blends. Specifically, the performance of the ternary system with two FREAs having quite different dipole moment terminals is worse compared to that with similar terminal dipole moments. The pair with larger difference in the dipole moment will also negatively impact device performance. This interesting phenomenon is likely due to the fact that very different dipole moments of terminals in FREAs can significantly decrease the electron mobility as well as induce unbalanced hole/electron transport. Consequently, it results in increased charge recombination and reduced charge collection efficiency. This finding demonstrates that the dipole moment of FREAs should be taken into account in designing ternary OSCs.

All-inorganic perovskite solar cells (PVSCs) have drawn increasing attention because of their outstanding thermal stability. However, their performance is still inferior than the typical organic-inorganic counterparts, especially for the devices with p-i-n configuration. Herein, we successfully employ a Lewis base small molecule to passivate the inorganic perovskite film, and its derived PVSCs achieved a champion efficiency of 16.1% and a certificated efficiency of 15.6% with improved photostability, representing the most efficient inverted all-inorganic PVSCs to date. Our studies reveal that the nitrile (C-N) groups on the small molecule effectively reduce the trap density of the perovskite film and thus significantly suppresses the non-radiative recombination in the derived PVSC by passivating the Pb-exposed surface, resulting in an improved open-circuit voltage from 1.10 V to 1.16 V after passivation. This work provides an insight in the design of functional interlayers for improving efficiencies and stability of all-inorganic PVSCs., There has been a hot competition to optimize the device performance for all-inorganic perovskite solar cells. Here Wang et al. employ a Lewis base molecule to suppresses the non-radiative recombination in the inverted device and achieve a champion efficiency of 16.1%.

A series of charge-neutral bis-tridentate Ir(III) complexes (1, 3, and 4) were prepared via employing three distinctive tridentate prochelates, that is, (pzptBphFO)H2, [(phpyim)H2·(PF6)], and [(pim...

The deep-level traps induced by charged defects at the grain boundaries (GBs) of polycrystalline organic–inorganic halide perovskite (OIHP) films serve as major recombination centres, which limit the device performance. Herein, we incorporate specially designed poly(3-aminothiophenol)-coated gold (Au@PAT) nanoparticles into the perovskite absorber, in order to examine the influence of plasmonic resonance on carrier dynamics in perovskite solar cells. Local changes in the photophysical properties of the OIHP films reveal that plasmon excitation could fill trap sites at the GB region through photo-brightening, whereas transient absorption spectroscopy and density functional theory calculations correlate this photo-brightening of trap states with plasmon-induced interfacial processes. As a result, the device achieved the best efficiency of 22.0% with robust operational stability. Our work provides unambiguous evidence for plasmon-induced trap occupation in OIHP and reveals that plasmonic nanostructures may be one type of efficient additives to overcome the recombination losses in perovskite solar cells and thin-film solar cells in general., The incorporation of plasmonic core-shell nanostructures at the grain boundaries of perovskite films reduces the charge recombination loss through photo-brightening of trap states.

Hybrid metal-halide perovskite solar cells (PVSCs) have drawn unprecedented attention during the last decade due to their superior photovoltaic performance, facile and low-cost fabrication, and potential for roll-to-roll mass production and application for portable devices. Through collective composition, interface, and process engineering, a comprehensive understanding of the structure-property relationship and carrier dynamics of perovskites has been established to help achieve a very high certified power conversion efficiency (PCE) of 25.5%. Apart from material properties, the modified heterojunction design and device configuration evolution also play crucial roles in enhancing the efficiency. The adoption and/or modification of heterojunction structures have been demonstrated to effectively suppress the carrier recombination and potential losses in PVSCs. Moreover, the employment of multijunction structures has been shown to reduce thermalization losses, achieving a high PCE of 29.52% in perovskite/silicon tandem solar cells. Therefore, understanding the evolution of the device configuration of PVSCs from single junction, heterojunction to multijunction designs is helpful for the researchers in this field to further boost the PCE beyond 30%. Herein, we summarize the evolution and progress of the single junction, heterojunction and multijunction designs for high-performance PVSCs. A comprehensive review of the fundamentals and working principles of these designs is presented. We first introduce the basic working principles of single junction PVSCs and the intrinsic properties (such as crystallinity and defects) in perovskite films. Afterwards, the progress of diverse heterojunction designs and perovskite-based multijunction solar cells is synopsized and reviewed. Meanwhile, the challenges and strategies to further enhance the performance are also summarized. At the end, the perspectives on the future development of perovskite-based solar cells are provided. We hope this review can provide the readers with a quick catchup on this emerging solution-processable photovoltaic technology, which is currently at the transition stage towards commercialization.

In this work, we successfully achieved a record fill factor (FF) of near 80% by using random copolymerization strategy to precisely control the morphology of active layer for polymer solar cells (PSCs). A series of random copolymers were synthesized by random copolymerization of a self-assembly third unit into the multithiophene-based polymer matrix. The random copolymers possess excellent room temperature processing performance due to their relatively weaker self-aggregation properties. More importantly, despite the non-irregular sequence of random copolymers, the planarity of the third unit favored by the S⋅⋅⋅O intramolecular interaction still induced a face-on orientation of the random copolymers and formed a homogeneously fibril-like interpenetrating network structure in the blend films. Ultimately, the random polymer-based device achieved a remarkably high fill factor (FF) near 80% without any treatment, even approaching to the values of the inorganic materials-based solar cells.

Summary Among all the solutions to improve long-term stability of perovskite solar cells, p-i-n heterojunction with all-metal-oxide charge transporting layers show their attractive features. However, these devices require an efficient electron-transporting layer (ETL) fabricated on top of the perovskites in which the commonly used oxide nanocrystals are limited by their imperfect surface. Here, a novel surface-passivation strategy was adopted by anchoring ZnO nanoparticles with fullerene nano-shells (Fa-ZnO) to mitigate trap states and passivate surface hydroxyl groups. We evidence the Fa-ZnO can be easily processed on top of perovskite as a high-quality ETL that improves electron extraction efficiency and suppresses ion diffusion/moisture penetration. In addition, the presence of fullerene shells allows Fa-ZnO nanoparticles to penetrate into perovskite precursors before crystallization, resulting in n-type sensitized configuration. With mesoscopic NiOx as hole-collecting contact, the p-n dual sensitization configuration has enabled all-metal-oxide devices to achieve state-of-the-art efficiencies of 21.1% with greatly improved performance longevity.

Organic semiconductors combining high mobility and efficient solid fluorescence are in high demand for developing organic light-emitting transistors and electrically driven organic lasers. But, achieving such dual functional molecules is extremely challenging. In this manuscript, we report 2-phenylbenzo[g]furo[2,3-b]quinoxaline derivatives (3a–3c) and develop a new synthesis method for the furo[2,3-b]quinoxaline core. It was found that 3a exhibited favorable aggregation induced emissive enhancement behavior and reasonable hole mobility. The absolute photoluminescence quantum yield of 3a is determined to be 22.1% in solid powders and can reach a maximum of 19.7% in 50% water in THF, twice that in CH2Cl2 solution (9.2%) and dispersed in PS film (9.3%). The single crystal and thin film organic field-effect transistor of 3a show a hole mobility of 2.58 × 10−2 cm2 V−1 s−1 and 5.7 × 10−3 cm2 V−1 s−1, respectively. Our results demonstrated that the 2-phenyl-benzo[g]furo[2,3-b]quinoxaline skeleton is a promising candidate for building multifunctional organic optoelectronics.

Although various self-healing polymers have been developed, individual designs are generally limited to a narrow range of possible mechanical properties and self-healing temperatures, as it's challenging to tune these characteristics over a wide range without re-engineering the molecular structure entirely. Here, a strategy to decouple self-healing and mechanical properties from the covalent structure of supramolecular polymers and a novel material system developed using this strategy, which is based on non-covalent π–π interactions between naphthalene diimide (NDI) and pyrene (Py) derivatives, are reported. Through targeted, stoichiometric addition of small model compounds, both binding strength and overall density of crosslinking interactions are modulated successfully. This strategy allows us to tune both self-healing temperature (30–60 °C) and Young's modulus (63–250 MPa) of our materials over a wide range, without changing the structure of polymer components. Our self-healing polymer system also displays good solid-state ionic conductivity (>10−5 S cm−1 at room temperature) after doping with Li(G4)TFSI, and could function as a cathode binder in lithium–sulfur batteries to give a high discharge capacity of 1109 mA h g−1 at C/5. The rational design strategy and resultant material platform demonstrated represent a first step towards a class of highly tunable self-healing polymers, for electrochemical devices.

We present a strategy for suppressing the open-circuit voltage (Voc) loss of perovskite solar cells by incorporating large guanidinium cations (Gua+) into a perovskite lattice, leading to a significantly improved Voc of 1.19 V and an impressive power conversion efficiency of >21%. Our results manifest the critical role of Gua in passivating defects and highlight the importance of compositional engineering in promoting the performance of perovskites.

Lithium–sulfur (Li–S) batteries hold great promise as a next-generation energy-storage technology. Their practical application, however, is hindered by the rapid capacity fading associated with the dissolution of lithium polysulfides (LiPSs) into organic electrolytes. In this work, we successfully impede these losses by anchoring thiol (–SH) functional groups to the nonpolar surface of a mesoporous carbon host. This new strategy increases the surface polarity of conductive carbons and traps LiPSs inside cathodes. By utilizing various spectroscopic methods, we investigate the mechanisms of LiPS trapping, which originate from the electrostatic and covalent interactions of the thiol functional groups with Li+ from the electrolyte and with S from the LiPS chains, respectively. Here, we for the first time identify the multiple interactions that are induced by a small molecular interface upon cycling and correlate them with the electrochemical behavior. The fundamental insight on the thiol functionality suggests a further rational design of multi-functional interfaces to achieve better Li–S performance.

High quality small-bandgap hybrid perovskites (AMX3 with M = Pb1−xSnx) are pivotal for all-perovskite multi-junction photovoltaics. The bandgap of these alloys significantly deviates from the linear interpolation between the bandgaps of APbI3 and ASnI3 for all A-site cations examined thus far. This non-linearity of the bandgap with composition is referred to as bandgap bowing. Here, we explore a wide-range of A-site compositions to understand bandgap bowing and identify the optimal Pb–Sn alloy composition. Optical and structural investigations of different APb1−xSnxI3 alloys reveal that the bandgap bowing is correlated with the extent of microstrain in their respective APbI3 compounds. We discover that bandgap bowing in APb1−xSnxI3 alloys is primarily due to local structural relaxation effects (changes in bond angles and lengths) that result from the size, shape, and charge distribution of the cations on the A-site, and that these effects are intimately coupled with chemical effects (intermixing of atomic orbitals) that result from changes in the M-site. The choice of X-site also impacts bandgap bowing because of the X-site anions' influence on local structural relaxation and chemical effects. Further, we extend these results to provide a general rationale for the origin and modulation of bandgap bowing in HP alloys. Subsequently, using high-throughput combinational spray coating and photoluminescence analysis, we find that ternary combinations of methylammonium (MA), formamidinium (FA), and cesium (Cs) are beneficial to improve the optoelectronic quality of APb1−xSnxI3 alloys. The optimal composition, (MA0.24FA0.61Cs0.15)(Pb0.35Sn0.65I3)I3 has a desirable low bandgap (1.23 eV) and high optoelectronic quality (achieving 86% of the detailed balance limit quasi-Fermi level splitting). This study provides valuable insights regarding bandgap evolution in HP alloys and the optimal small-bandgap absorber composition desired for next-generation HP tandems.

We report on a method of precursor engineering to prepare high quality and stable perovskites based on formamidinium/methylammonium (FAMA) mixed-cations. CsI is commonly used to inhibit the photoinactive phase in FAMA perovskites. However, the hydrophilic nature of CsI would result in a structural instability issue at high relative humidity (RH). Besides, in inverted perovskite solar cells (PSCs) based on organic hole transport layers, the low conduction band minimum (CBM) of FAMA perovskites would lead to small open circuit voltage (Voc) (∼1.0 V), and thus additional surface passivation/modification layers are normally employed, indicating that it is essential to improve the basic precursors for high quality perovskite films. Herein, the proposed method is realized via ternary precursor alloying which endows the perovskite with increased grain size, enhanced crystallinity, reduced trap states, and a pure photoactive phase without the assistance of CsI. Without passivation/modification layers, the device Voc is enhanced markedly from 1.0 V to 1.1 V on average, and a champion power conversion efficiency of 20.7% with negligible hysteresis is achieved. Moreover, as they are free of hydrophilic CsI, both the photoactive perovskite films and devices exhibit excellent stability in ambient air. At high RH (70%), the optimized device without encapsulation only loses 16% of its efficiency after 1000 h storage, indicating the potential for the development of efficient and stable PSCs.

We explore the effects of nonradiative recombination at the extracting contacts on the achievable performance of halide perovskite photovoltaic cells. First, we perform device simulations using standard drift-diffusion models with experimental semiconductor parameters matching those of methylammonium lead triiodide (MAPbI3). We quantify the range of surface recombination velocities (SRVs) that would allow this archetypal perovskite to reach power conversion efficiencies of 27%. In particular, for contacts with well-aligned energy levels, SRVs of ∼1–10 cm/s should enable open-circuit voltages of 1.30 V, within 96% of the Shockley–Queisser limit. Next, we use time-resolved photoluminescence to experimentally determine the SRVs on 14 different common electron- and hole-extracting contacts, including TiO2, SnO2, ZnO, PCBM, ITIC, ICBA, TPBi, PEDOT:PSS, PTAA, PVK, NiO, MoO3, WO3, and spiro-OMeTAD. These results point the way to the selection and rational engineering of better contacts as a means to achieve high...

Delicately designed dopant-free hole-transporting materials (HTMs) with ordered structure have become one of the major strategies to achieve high-performance perovskite solar cells (PSCs). In this work, we report two donor-π linker-donor (D-π-D) HTMs, N01 and N02, which consist of facilely synthesized 4,8-di(n-hexyloxy)-benzo[1,2-b:4,5-b']dithiophene as a π linker, with 10-bromohexyl-10H-phenoxazine and 10-hexyl-10H-phenoxazine as donors, respectively. The N01 molecules form a two-dimensional conjugated network governed by C-H⋅⋅⋅O and C-H⋅⋅⋅Br interaction between phenoxazine donors, and synchronously construct a three-dimension lamellar structure with the aid of interlaminar π-π interaction. Consequently, N01 as a dopant-free small-molecule HTM exhibits a higher intrinsic hole mobility and more favorable interfacial properties for hole transport, hole extraction and perovskite growth, enabling an inverted PSC to achieve a very impressive power conversion efficiency of 21.85 %.

Solution-processed organic solar cells (OSCs) are a promising candidate for next-generation photovoltaic technologies. However, the short exciton diffusion length of the bulk heterojunction active layer in OSCs strongly hampers the full potential to be realized in these bulk heterojunction OSCs. Herein, we report high-performance OSCs with a pseudo-bilayer architecture, which possesses longer exciton diffusion length benefited from higher film crystallinity. This feature ensures the synergistic advantages of efficient exciton dissociation and charge transport in OSCs with pseudo-bilayer architecture, enabling a higher power conversion efficiency (17.42%) to be achieved compared to those with bulk heterojunction architecture (16.44%) due to higher short-circuit current density and fill factor. A certified efficiency of 16.31% is also achieved for the ternary OSC with a pseudo-bilayer active layer. Our results demonstrate the excellent potential for pseudo-bilayer architecture to be used for future OSC applications., The so-called pseudo-bilayer (PB) organic solar cell (OSC) device architecture can promote enhanced exciton dissociation and charge transport, leading to improved device performance. Here, the authors report high-efficiency OSCs that features a PB architecture and optimized ternary system.

The active layer morphology transition of organic photovoltaics under non-equilibrium conditions are of vital importance in determining the device power conversion efficiency and stability; however, a general and unified picture on this issue has not been well addressed. Using combined in situ and ex situ morphology characterizations, morphological parameters relating to kinetics and thermodynamics of morphology evolution are extracted and studied in model systems under thermal annealing. The coupling and competition of crystallization and demixing are found to be critical in morphology evolution, phase purification and interfacial orientation. A unified model summarizing different phase diagrams and all possible kinetic routes is proposed. The current observations address the fundamental issues underlying the formation of the complex multi-length scale morphology in bulk heterojunction blends and provide useful morphology optimization guidelines for processing devices with higher efficiency and stability., Designing efficient blue perovskite LEDs by using mixed halides perovskite is still a challenge, limited mainly by the phase segregation issue. Here, the authors demonstrate in situ fabrication of quasi-2D CsPbClBr2 nanocrystal films with mixed ligands to overcome the constraint.

This chapter discusses the approaches in the optimization of molecular and material nonlinear optical and thermal properties. Organic polymeric electro-optic (E-O) materials have attracted significant attention because of their potential use as fast and efficient components of integrated photonic devices. The factors that affect the material thermal stability are the inherent thermal stability of the nonlinear optical (NLO) chromophores, the chemical stability of the NLO chromophores during polymer processing, and the long-term dipolar alignment stability at high temperatures. Although considerable progress has been made in achieving these properties, organic polymeric materials suitable for practical E-O device applications are yet to be developed. To overcome these deficiencies associated with the tricyanovinyl group, 2 was further modified by replacing the most reactive CN in the tricyanovinyl group with aryl groups. The new molecular systems and their properties presented in this chapter provide insights into the many practical issues relevant to the material development.

Owing to their large absorption cross-sections and high photoluminescence quantum yields, lead halide perovskite quantum dots (PQDs) are regarded as a promising candidate for various optoelectronics applications. However, easy degradation of PQDs in water and in a humid environment is a critical hindrance for applications. Here we develop a Pb-S bonding approach to synthesize water-resistant perovskite@silica nanodots keeping their emission in water for over six weeks. A two-photon whispering-gallery mode laser device made of these ultra-stable nanodots retain 80% of its initial emission quantum yield when immersed in water for 13 h, and a two-photon random laser based on the perovskite@silica nanodots powder could still operate after the nanodots were dispersed in water for up to 15 days. Our synthetic approach opens up an entirely new avenue for utilizing PQDs in aqueous environment, which will significantly broaden their applications not only in optoelectronics but also in bioimaging and biosensing., Lead halide perovskite quantum dots (PQDs) promise applications in optoelectronics but are limited by sensitivity to wet environments. Here the authors develop a Pb-S bonding approach to synthesize PQDs@silica nanodots that are capable of emitting and lasing in aqueous environments for long periods.

Due to the vigorous development of polymerized small-molecule acceptors (PSMAs), all-polymer solar cells (all-PSCs) have made tremendous advancement recently. However, their power conversion efficiencies (PCEs) are still restricted by the lack of PSMAs with desirable optoelectronic properties, especially the ability to capture the near-infrared photons. To resolve this, two near-infrared absorbing PSMAs, namely PY2Se-F and PY2Se-Cl, with a selenophene-fused core and halogenated end-group are developed. Combining the synergistic effects of selenium and fluorine (F)/chlorine (Cl) substitutions in broadening absorption and enhancing intermolecular interactions, PY2Se-F and PY2Se-Cl show significantly red-shifted absorption (30–40 nm) and reasonably deep-shifted lowest unoccupied molecular orbital (LUMO) levels compared with the pristine PY2S-H and fluorinated PY2S-F. When replacing F with Cl on the end-group, the PY2Se-Cl shows a better blend morphology with polymer donor PM6, compared with the PY2Se-F-based one, leading to better charge transport. As a result, the PM6:PY2Se-Cl-based all-PSCs achieve an impressive PCE of 16.1% with both high short-circuit current density (Jsc) of 24.5 mA cm−2 and fill factor (FF) of 0.743, which are among the highest values in the reported binary all-PSCs so far. Notably, this is the first example of chlorinated end-group derived PSMAs. Combining with the low-cost merit of chlorination, PY2Se-Cl shows great potential in the practical applications of efficient all-PSCs.

Simultaneously achieving high efficiency, long-term stability, and robust fabrication with good reproducibility in perovskite solar cells (PVSCs) is essential for their practical applications. Herein, we first demonstrate a thick TiO2 backbone film directly on top of a perovskite film through a simple room-temperature solution process. Through the strategy of decorating the TiO2 film with fullerene for passivating traps and filling voids, we achieve a fullerene-decorated TiO2 electron transport layer (ETL) in inverted PVSCs. Because of the suppressed monomolecular Shockley–Read–Hall recombination and ion diffusion of the fullerene-decorated TiO2 ETL, stabilized efficiencies of ∼20% and shelf life stability remaining over 98% of initial efficiency after aging in ambient conditions or 16 months are achieved. Remarkably, the PVSCs are insensitive to TiO2 thickness from 50 to 250 nm, which contributes significantly to the robust fabrication and high reproducibility of the PVSCs. This work provides an ETL desi...

The state-of-the-art solution-processed perovskite solar cells (PVSCs) have reached the compelling power conversion efficiency (PCE) of 22.1%, comparable with most of the current single-junction nonconcentrated commercialized solar cells. However, the development of scalable printing and coating techniques compatible with the fabrication of PVSCs in ambient conditions still lags behind, due to the following two reasons: 1) The ambient oxygen and moisture significantly degrade the characteristics and functionality of the perovskite films, and 2) most of the research groups focus on the lab-scale spin-coating, hindering gaining knowledge and experience required to understand and employ scalable methods. In this paper, we fabricated all layers of the PVSCs, except for the back contact, by scalable blade-coating method, performed in ambient conditions, and achieved a high PCE of 11.1%, with superior device stability. Through selecting a nonhalide source and strong reducing agent, we alleviated the oxidation problem in ambient conditions. Moreover, we found an optimized blade-coater substrate temperature of 125 °C, which can yield micrometer-scale perovskite domain size created by thermocapillary Marangoni motion, high crystallinity, large absorption, and prolonged carrier lifetime. These results are promising for manufacturing PVSCs in high volume and in ambient conditions.

We demonstrate that the electro-optic (EO) modulation response linearly decreases (dB scale) with respect to the modulating frequency, with an extremely small drop of less than 2 dB, up to a limit of 67 GHz, as measured by an optical component analyzer. The measured bandwidth of the EO response is wider than 67 GHz and was extrapolated to 120 GHz. This study demonstrates a new optimized broadband optical modulator with low half-wave voltage and low optical loss. The dielectric constant of each material in the modulator is accurately measured by comparing the electrical transmission and reflection parameters for the radio frequency (RF) high-speed coplanar electrode deposited on each layer with theoretically obtained values. The electrical transmission bandwidth for the optimized RF electrode is measured up to a limit of 110 GHz by a vector network analyzer and then extrapolated to a 6-dB bandwidth of 130 GHz based on the experimental parameters. The product of the half-wave voltage and electrode length is 1.8 V⋅cm for dual-drive operation. The in-device EO coefficient is 160 pm/V at 1.55 μm. The product of the half-wave voltage and loss is 10.8 V⋅dB.

We study photoinduced charge generation in a model polymer/nonfullerene acceptor (NFA) organic photovoltaic (OPV) blend. Specifically, we focus on hole-transfer kinetics from the photoexcited NFA thiophene-thieno[3,2-b]thiophene-thiophene-3-(dicyanomethylidene)indan-1-one (4TIC) to the conjugated polymer donor poly[(4,4′-bis(2-butyloctoxycarbonyl-[2,2′-bithiophene]-5,5-diyl)-alt-(2,2′-bithiophene-5,5′-diyl)] (PDCBT) using ultrafast transient absorption spectroscopy by selectively exciting the 4TIC electron acceptor and monitoring the bleach of the PDCBT ground-state population. In the blend, the 4TIC excitons decay with an average lifetime of 7 ps, accompanied by a concomitant rise in the ground-state bleach of the polymer with a comparable average lifetime that is 60% complete by 8 ps and 95% complete by 100 ps, occurring roughly an order of magnitude slower than that in most previously reported polymer/NFA blends. Notably, the ground-state bleach of the polymer continues to grow, not reaching its maximu...

Quasi-2D perovskites are attractive because of their improved stability compared to 3D counterparts, but they suffer from reduced performance. Here we report an efficient quasi-2D perovskite (PEA)2(MA)4Pb5I16-based optoelectronic device processed with NH4SCN and NH4Cl additives, showing a stabilized photovoltaic power conversion efficiency as high as 14.1% (average value 12.9 ± 0.8%), which is among the highest-performing quasi-2D perovskite solar cells. These additives increase the perovskite crystallinity and induce a preferred orientation with the (0k0) planes perpendicular to the substrate, resulting in improved transport properties and hence increased short-circuit current density. Furthermore, the NH4Cl treatment enriches the Cl– concentration near the PEDOT:PSS/perovskite interface, which passivates the electron traps, leading to an enhanced electroluminescence external quantum efficiency (0.68% at +2.5 V bias). As a result, high open-circuit voltages of 1.21 ± 0.01 V with a record low nonradiative...

We study how tailoring noncovalent interactions through the regiochemistry of common donor–acceptor polymers can alter their excited-state electronic properties. Specifically, we compare two regioregular analogues (referred to as P1 and P2) of the widely used donor–acceptor copolymer poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-co-3-fluorothieno[3,4-b]thiophene-2-carboxylate], which differ only in the orientation of a fluorine atom on the thieno[3,4-b]thiophene acceptor units with respect to the benzodithiophene unit. We show that in thin films, this subtle change along the polymer backbone results in a transformation from typical H-like to an unusual HJ-like aggregate behavior, indicating significant differences in intrachain exciton coupling along the polymer backbone and interchain coupling between polymer chains. We also use electroabsorption spectroscopy to relate the dominant coupling mechanisms to differences in the excess polarization volume of the excitons in P1 and P...

Two novel non-fullerene acceptors, SN6IC and SN6IC-4F, based on an S,N-heteroacene backbone were designed and synthesized. The cyclopentadiene fragments of commonly used acceptors were replaced with pyrrole rings to improve the electron-donating ability to increase the energy levels of the molecules. Both acceptors match well with the absorption and energy levels of the polymer donor PBDB-T, and PBDB-T:SN6IC-4F-based solar cells showed an excellent power conversion efficiency of 13.2%, with a relatively small VOC loss of 0.54 eV. This study proves that the introduction of a nitrogen atom to replace the sp3-hybridized carbon in the fused ring is very effective for making highly efficient NFAs to further improve the performance of organic solar cells.

Organic–inorganic hybrid perovskites are promising materials for optoelectronic applications. Solution-processed films typically possess deleterious randomly oriented grains that limit their potential. Here, we report growth of highly oriented methylammonium lead bromide (MAPbBr3) films through ion exchange from 2D to 3D perovskite. We first investigate the ion exchange reaction mechanism for conversion between 2D and 3D perovskites using a combined experimental and theoretical approach. The selectivity of conversion is governed by thermodynamics and kinetics of the ion exchange reaction and is intimately linked to the molecular structure of the organic cation in 2D perovskite. Subsequently using the derived insights, we chose phenylethylammonium lead bromide (PEA2PbBr4) as the 2D growth template and successfully exchanged it into high-quality 3D MAPbBr3 films with strong uniaxial 100 orientation. The enhanced film quality leads to ultranarrow electroluminescence spectra (15.3 nm fwhm and 98.10% color pur...

The open-circuit voltages (VOC) of hybrid perovskite (HP) solar cells do not increase sufficiently with increasing bandgap (for Eg > 1.70eV). We study the impact of A+ size mismatch induced lattice distortions (in ABX3 structure) on the optoelectronic quality of high-bandgap HPs and find that the highest quality films have high A-site size-mismatch, where large guanidinium (GA) compensates for small Cs to keep the tolerance factor in the range for the perovskite structure. Specifically, we find that 1.84eV bandgap (FA0.33GA0.19Cs0.47)Pb(I0.66Br0.34)3 and 1.75eV bandgap (FA0.58GA0.10Cs0.32)Pb(I0.73Br0.27)3 attain quasi-Fermi level splitting of 1.43eV and 1.35eV, respectively, which is >91% of the Shockley-Queisser limit for both cases. Films of 1.75eV bandgap (FA,GA,Cs)Pb(I,Br)3 are then used to fabricate p-i-n photovoltaic devices that have a VOC of 1.24 V. This VOC is among the highest VOC reported for any HPs with similar bandgap (1.7 to 1.8 eV) and a substantial improvement for the p-i-n architecture, ...