吴晓晓

A model ferroelectric photocatalyst, BaTiO₃, was treated with NaBH₄ to introduce surface oxygen vacancies (Ov‐BTO). The resultant material offers spin‐polarized regulation and an increased internal electric field (IEF). The function of Ov‐induced photocatalytic activity under an external magnetic field is explored and the positive effect of the external magnetic field phenomenon demonstrated on photocatalytic N₂ fixation.

Abstract

Efficient coupling solar energy conversion and N₂ fixation by photocatalysis has been shown promising potentials. However, the unsatisfied yield rate of NH₃ curbs its forward application. Defective typical perovskite, BaTiO₃, shows remarkable activity under an applied magnetic field for photocatalytic N₂ fixation with an NH₃ yield rate exceeding 1.93 mg L⁻¹ h⁻¹. Through steered surface spin states and oxygen vacancies, the electromagnetic synergistic effect between the internal electric field and an external magnetic field is stimulated. X‐ray absorption spectroscopy and density functional theory calculations reveal the regulation of electronic and magnetic properties through manipulation of oxygen vacancies and inducement of Lorentz force and spin selectivity effect. The electromagnetic effect suppresses the recombination of photoexcited carriers in semiconducting nanomaterials, which acts synergistically to promote N₂ adsorption and activation while facilitating fast charge separation under UV‐vis irradiation.

A thermally stable perovskite solar cell is developed by capturing mobile lithium ions using a new molecular hole transporter, 1,3‐bis(5‐(4‐(bis(4‐methoxyphenyl)amino)phenyl)thieno[3,2‐b]thiophen‐2‐yl)‐5‐octyl‐4H‐thieno[3,4‐c]pyrrole‐4,6(5H)‐dione (coded HL38), where a strong interaction of the lithium ions in lithium bis(trifluoromethanesulfonyl)imide with the 5‐octylthieno[3,4‐c]pyrrole‐4,6‐dione (octyl‐TPD) moiety in HL38 is responsible for maintaining ≈86% of the initial power conversion efficiency for over 1000 h at 85 °C.

Abstract

A thermally stable perovskite solar cell (PSC) based on a new molecular hole transporter (MHT) of 1,3‐bis(5‐(4‐(bis(4‐methoxyphenyl) amino)phenyl)thieno[3,2‐b]thiophen‐2‐yl)‐5‐octyl‐4H‐thieno[3,4‐c]pyrrole‐4,6(5H)‐dione (coded HL38) is reported. Hole mobility of 1.36 × 10⁻³ cm² V⁻¹ s⁻¹ and glass transition temperature of 92.2 °C are determined for the HL38 doped with lithium bis(trifluoromethanesulfonyl)imide and 4‐tert‐butylpyridine as additives. Interface engineering with 2‐(2‐aminoethyl)thiophene hydroiodide (2‐TEAI) between the perovskite and the HL38 improves the power conversion efficiency (PCE) from 19.60% (untreated) to 21.98%, and this champion PCE is even higher than that of the additive‐containing 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (spiro‐MeOTAD)‐based device (21.15%). Thermal stability testing at 85 °C for over 1000 h shows that the HL38‐based PSC retains 85.9% of the initial PCE, while the spiro‐MeOTAD‐based PSC degrades unrecoverably from 21.1% to 5.8%. Time‐of‐flight secondary‐ion mass spectrometry studies combined with Fourier transform infrared spectroscopy reveal that HL38 shows lower lithium ion diffusivity than spiro‐MeOTAD due to a strong complexation of the Li⁺ with HL38, which is responsible for the higher degree of thermal stability. This work delivers an important message that capturing mobile Li⁺ in a hole‐transporting layer is critical in designing novel MHTs for improving the thermal stability of PSCs. In addition, it also highlights the impact of interface design on non‐conventional MHTs.

A new pyridine‐based polymer semiconductor (PPY2) was introduced as the dopant‐free hole‐transporting material in inverted perovskite solar cells. It exhibits suitable energy levels, high hole mobility, effective passivation effects, and the capability of promoting the formation of a high‐quality polycrystalline perovskite film. The devices based on PPY2 delivered an encouraging power‐conversion efficiency up to 22.41 % with a high V _OC of 1.16 V.

Abstract

Currently, the performance improvement for inverted perovskite solar cells (PVSCs) is mainly limited by the high open circuit voltage (V _OC) 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 V _OC 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.

(NiCo)_1−y Fe _y O _x decorated GO is used as a hole booster in all‐inorganic CsPbIBr₂ PSC. A champion efficiency of 10.95 % is achieved arising from the charge transfer doping effect between (NiCo)_1−y Fe _y O _x and GO.

Abstract

The precise regulation of interfacial charge distribution highly determines the power conversion efficiency of perovskite solar cells (PSCs). Herein, inorganic (NiCo)_1−y Fe _y O _x nanoparticle decorated graphene oxide (GO) is successfully demonstrated as a hole booster for all‐inorganic CsPbIBr₂ PSC free of precious metal electrode. Arising from the spontaneous electron transfer induced p‐type doping of GO from edged oxygen‐containing functional groups to (NiCo)_1−y Fe _y O _x , the best all‐inorganic CsPbIBr₂ PSC achieves an efficiency of 10.95 % under one standard sun owing to the eliminated paradox between charge extraction and charge localization in GO surface. Furthermore, the champion device exhibits an excellent long‐term stability at 10 % relative humidity without encapsulation over 70 days because of the suppressed ions migration.

Combining the layer‐by‐layer processing method and a ternary strategy, 18.16% efficiency, which is among the highest values reported to date, is achieved in single‐junction organic photovoltaics (OPVs) based on the PM6:BO‐4Cl:BTP‐S2 blend, superior to that (18.03%) of bulk‐heterojunction OPVs, proving that layer‐by‐layer processed ternary OPVs could be a promising approach to high efficiencies.

Abstract

Obtaining a finely tuned morphology of the active layer to facilitate both charge generation and charge extraction has long been the goal in the field of organic photovoltaics (OPVs). Here, a solution to resolve the above challenge via synergistically combining the layer‐by‐layer (LbL) procedure and the ternary strategy is proposed and demonstrated. By adding an asymmetric electron acceptor, BTP‐S2, with lower miscibility to the binary donor:acceptor host of PM6:BO‐4Cl, vertical phase distribution can be formed with donor‐enrichment at the anode and acceptor‐enrichment at the cathode in OPV devices during the LbL processing. In contrast, LbL‐type binary OPVs based on PM6:BO‐4Cl still show bulk‐heterojunction like morphology. The formation of the vertical phase distribution can not only reduce charge recombination but also promote charge collection, thus enhancing the photocurrent and fill factor in LbL‐type ternary OPVs. Consequently, LbL‐type ternary OPVs exhibit the best efficiency of 18.16% (certified: 17.8%), which is among the highest values reported to date for OPVs. The work provides a facile and effective approach for achieving high‐efficiency OPVs with expected morphologies, and demonstrates the LbL‐type ternary strategy as being a promising procedure in fabricating OPV devices from the present laboratory study to future industrial production.

The effect of phenethylammonium iodide (PEAI) deposition is investigated for indoor perovskite solar cells (PSCs). With an optimized amount of PEAI, homogenous extraction of photo‐generated carriers is observed. In addition, work function shifts toward the valence band of the surface. This results in enhanced hole collection between the hole transport layer and perovskite interfaces leading to improved performance of indoor PSCs.

Abstract

Halide perovskite‐based photovoltaic (PV) devices have recently emerged for low energy consumption electronic devices such as Internet of Things (IoT). In this work, an effective strategy to form a hole‐selective layer using phenethylammonium iodide (PEAI) salt is presented that demonstrates unprecedently high open‐circuit voltage of 0.9 V with 18 µW cm⁻² under 200 lux (cool white light‐emitting diodes). An appropriate post‐deposited amount of PEAI (2 mg) strongly interacts with the perovskite surface forming a conformal coating of PEAI on the perovskite film surface, which improves the crystallinity and absorption of the film. Here, Kelvin probe force microscopy results indicate the diminished potential difference across the grain boundaries and grain interiors after the PEAI deposition, constructing an electrically and chemically homogeneous surface. Also, the surface becomes more p‐type with a downshift of a valence band maximum, confirmed by ultraviolet photoelectron spectroscopy measurement, facilitating the transport of holes to the hole transport layer (HTL). The hole‐selective layer‐deposited devices exhibit reduced hysteresis in light current density–voltage curves and maintain steadily high fill factor across the different light intensities (200–1000 lux). This work highlights the importance of the HTL/perovskite interface that prepares the indoor halide perovskite PV devices for powering IoT device.

Lead halide perovskites are well known for their facile crystallization due to their ionic nature. Herein, the synthesis and characterization of amorphous lead halide thin films are reported. The amorphous lead halide perovskite has a large and tunable optical bandgap and improves the photoluminescence quantum yield and lifetime of incorporated crystalline perovskite.

Abstract

Lead halide perovskites are among the most exciting classes of optoelectronic materials due to their unique ability to form high‐quality crystals with tunable bandgaps in the visible and near‐infrared using simple solution precipitation reactions. This facile crystallization is driven by their ionic nature; just as with other salts, it is challenging to form amorphous halide perovskites, particularly in thin‐film form where they can most easily be studied. Here, rapid desolvation promoted by the addition of acetate precursors is shown as a general method for making amorphous lead halide perovskite films with a wide variety of compositions, including those using common organic cations (methylammonium and formamidinium) and anions (bromide and iodide). By controlling the amount of acetate, it is possible to tune from fully crystalline to fully amorphous films, with an interesting intermediate state consisting of crystalline islands embedded in an amorphous matrix. The amorphous lead halide perovskite has a large and tunable optical bandgap. It improves the photoluminescence quantum yield and lifetime of incorporated crystalline perovskite, opening up the intriguing possibility of using amorphous perovskite as a passivating contact, as is currently done in record efficiency silicon solar cells.

A simple, generic, and effective approach toward high‐performance, stretchable outdoor and indoor organic photovoltaic is reported, and a high power conversion efficiency (PCE) of 15.3% under 1 sun illumination is achieved. Under indoor illumination, the stretchable device shows a comparable performance (20.5% vs 20.8%) to glass/indium tin oxide (ITO)‐based devices. The stretchable device shows 1.5–2 times PCE a larger than rigid device at a large incident angle.

Abstract

Flexible photovoltaic devices are promising candidates for triggering the Internet of Things (IoT). However, the power conversion efficiencies (PCEs) of flexible organic photovoltaic (OPV) devices with high conductivity poly(3,4‐ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS) electrodes on plastic are lagging behind the rigid devices due to the low transmittance of polyethylene terephthalate (PET)/PEDOT:PSS. Moreover, the poor stretchability of the commonly used plastic substrates largely hinders the practical application of wearable devices. Herein, a novel stretchable indium tin oxide (ITO)‐free OPV device with a surface‐texturing polydimethylsiloxane (PDMS) substrate for outdoor strong‐ and indoor dim‐light energy harvesting is reported. The high diffuse transmittance and haze effect of the substrate enable stretchable ITO‐free devices, yielding a high PCE of 15.3% under 1 sun illumination. More excitingly, the stretchable device based on textured PDMS/PEDOT:PSS maintains a comparable PCE of 20.5% (20.8% for the rigid device) under indoor light illumination. Notably, the stretchable device is much more insensitive to the light direction, maintaining 38.5% of the initial PCE at an extremely small incident angle of 10° (16.3% for glass/ITO‐based counterpart). The texturing stretchable substrate provides a new direction for achieving high performance and enhanced light utilization for the stretchable light‐harvesting device, suitable for indoor and outdoor applications.

Flexible organic solar cells (OSCs) come to the forefront of organic electronics. It is critical to develop high‐merit flexible transparent electrodes (FTEs). The work covers the frontier progress of PEDOT:PSS, graphene, metallic nanostructures, metal oxide/metal/metal oxide, Mxene, and hybrid electrodes. It raises the awareness for the importance of developing the FTEs and reveals their critical role in flexible OSCs.

Abstract

Substantial effort has been devoted to both chemical doping and design of flexible transparent electrodes (FTEs) for flexible organic solar cells (OSCs) in the past decade. Poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate), graphene, metal nanostructures, metal oxide/ultrathin metal/metal oxide, Mxene, and their hybrid electrodes emerge to be the most promising flexible conducting materials over indium tin oxide. The FTE fabrications play a critical role in flexible OSCs. This feature review article summarizes the current status on the researches of the FTEs including various approaches and strategies to boost the conductivity, work function, mechanical flexibility, wettability, etc, which directly affect the performances of the flexible OSCs. The most cutting edge progresses on both FTEs and flexible OSCs are highlighted along the line. Advantages and plausible issues are pointed out. Perspectives are provided that can advance the developments of the flexible OSCs. This review raises the awareness for the importance of developing plenty of FTEs and reveals their critical role in flexible OSCs.

The photoinitiator bifunctional bis‐benzophenone is introduced into non‐fullerene solar cells as a multifunctional solid additive for the first time. The doping of this solid additive could not only modify the polymer order and firm morphology of active layer to improve device performance, but also to achieve better reproducibility, thickness insensitivity, and thermal stability for non‐fullerene solar cells.

Abstract

Simultaneously improving efficiency and stability is critical for the commercial application of non‐fullerene acceptor polymer solar cells (NFA‐PSCs). Multifunctional solid additives have been considered as a potential route to tune the morphology of the active layer and optimize performance. In this work, photoinitiator bifunctional bis‐benzophenone (BP‐BP) is used as a solid additive, replacing solvent additives, in the PBDB‐T:ITIC NFA system. With the addition of BP‐BP, the intermolecular π–π stacking of PBDB‐T and morphology is improved, leading to more balanced carrier transport and more effective exciton dissociation. Devices fabricated with BP‐BP show a power conversion efficiency (PCE) of 11.89%, with enhanced short‐circuit current (J _sc), and fill factor (FF). Devices optimized with BP‐BP show excellent reproducibility, insensitivity to thickness, and an improved thermal stability under atmospheric conditions without encapsulation. This work provides a new strategy for the application of solid additives in NFA‐PSCs.

It is found that the dynamic redistribution of mobile ions modifies the injection and transport property of charge carriers in the emissive layer, which can well explain the hysteresis in external quantum efficiency (EQE)– and radiance–voltage curves, as well as the rise phenomena of EQE and radiance under low constant driving voltages.

Abstract

Despite quick development of perovskite light‐emitting diodes (PeLEDs) during the past few years, the fundamental mechanisms on how ion migration affects device efficiency and stability remain unclear. Here, it is demonstrated that the dynamic redistribution of mobile ions in the emissive layer plays a key role in the performance of PeLEDs and can explain a range of abnormal behaviours commonly observed during the device measurement. The dynamic redistribution of mobile ions changes charge–carrier injection and leads to increased recombination current; at the same time, the ion redistribution also changes charge transport and results in decreased shunt resistance current. As a result, the PeLEDs show hysteresis in external quantum efficiencies (EQEs) and radiance, that is, higher EQEs and radiance during the reverse voltage scan than during the forward scan. In addition, the changes on charge injection and transport induced by the ion redistribution also well explain the rise of the EQE/radiance values under constant driving voltages. The argument is further rationalized by adding extra formamidinium iodide (FAI) into optimized PeLEDs based on FAPbI₃, resulting in more significant hysteresis and shorter operational stability of the PeLEDs.

Two acceptors of PCl and PCl‐Si are synthesized, and both acceptors have a similar unit that exists on the backbone of the donor PM6. The similar unit acts as a bridge to improve the interfacial interaction and miscibility between the donor and acceptor. The PM6:PCl‐based all‐polymer solar cell achieves a high fill factor of 70.25% and a high device stability.

Poor miscibility between the polymer donor and acceptor in the active layer leads to low fill factors (FF). PCl and PCl‐Si are synthesized by polymerization of the accessible and inexpensive IDIC‐C16 with BDT‐Cl and BDT‐Cl‐Si, respectively. PCl and PCl‐Si involve a BDT skeleton that is definitely used in most highly efficient polymer donors, such as PM6. Guided by the law of similarity and intermiscibility, the similar building block acts as a bridge to improve the interfacial interaction and miscibility between the donor and acceptor, leading to a favorable morphology of the active layer. It is found that the miscibility of the active layer is sensitive to the structural similarity degree of the similar unit of the donor and acceptor. The PCl‐Si‐based device delivers a power conversion efficiency (PCE) of 9.25% with a moderate FF of 67.86%, whereas the PM6:PCl‐based device achieves a PCE of 10.02% with a higher FF of 70.25%, which is the highest FF of the device with an IDIC‐C16‐based polymer acceptor. In addition, the improved interaction between the donor and acceptor improves the device stability. These results demonstrate that regulating the structural similarity between donor and acceptor is a promising strategy to optimize and stabilize morphology for high‐performance all‐polymer solar cells.

The effect of carbon–oxygen (CO)‐bridge isomerization is found to depend on the side‐chain and end‐group modifications. Their combined role determines the end‐group π–π stacking and aggregation behaviors of the CO‐bridge acceptor–donor–acceptor (A–D–A) acceptors.

For bulk heterojunction organic solar cells (OSCs), controlling molecular self‐aggregation during solution processing is crucial to obtain ideally phase‐separated morphology and high device performance. Recently, fused‐ring regiochemistry, for example, carbon–oxygen (CO)‐bridge isomerization, has been found to effectively modulate the aggregation structures and photovoltaic properties of acceptor–donor–acceptor (A–D–A) small‐molecule acceptors (SMAs). Strikingly, the relative aggregation ability for the CO‐bridge isomers turns out to be reverse after simultaneous replacement of the linear alkyl side chains with branched ones and fluorination of the end groups. Herein, to understand the molecular origin of such an observation, the aggregation behaviors of three pairs of CO‐bridge isomeric SMAs in solutions are systematically investigated by atomistic molecular dynamics simulations. Because of the large side‐chain steric hindrance around the fused‐ring core, the molecular self‐aggregation for all of these SMAs is dominated by end‐group π–π stacking. Moreover, the end‐group π–π interaction is controlled by the synergistic effect of CO‐bridge isomerization, side‐chain branching, and end‐group fluorination, which are responsible for the reversal of the aggregation ability of the isomeric SMAs. This work provides the rationalization of experimental observations and is helpful for modulating the blending morphologies for high‐efficiency OSCs based on CO‐bridge SMAs.

Highly efficient and mechanically robust flexible perovskite solar cells (PSCs) are obtained by using an HPbI₃ additive, which results in improved crystallinity and a decreased work function of the perovskite. The power conversion efficiencies (PCEs) of 20.1% and 18.74% are obtained for the PSCs on rigid and flexible substrates, respectively. The flexible PSCs maintain 70% of the original PCE after 5000 bending cycles.

High efficiency and mechanical stability are in great demand for commercial applications of the flexible perovskite solar cells (PSCs) in portable and wearable electronics. Herein, power conversion efficiency (PCE) and mechanical robustness of the methylammonium (MA)‐free flexible PSCs are simultaneously enhanced by incorporating a HPbI₃ additive with optimal content in the perovskite precursor solution. The HPbI₃ additive facilitates an improved morphology and crystallinity, as well as a decreased work function of the perovskite films, leading to improved device performance. As a result, PCEs of 20.1% and 18.74% are obtained for the rigid and flexible PSCs, respectively, which are among the best results for inverted MA‐free PSCs. The flexible PSCs maintain 95% and 70% of the initial PCE value after 1000 and 5000 bending cycles, respectively, at a bending radius of 4 mm. The current result reveals that using the HPbI₃ additive is a universal strategy to enhance performance of the flexible PSCs effectively and promote the development of the perovskite‐based photovoltaics.

Octyltrimethylammonium chloride is introduced into the MAPbI₃ perovskite precursor to reduce the open‐circuit voltage (V _OC) loss of printable mesoscopic perovskite solar cells (MPSCs) by optimizing energy‐level alignment of the TiO₂/perovskite heterojunction and suppressing nonradiative recombination. As a result, a power conversion efficiency (PCE) of 16.53% with an improved V _OC of 1007 mV is achieved for printable MPSCs.

Hole‐conductor‐free fully printable mesoscopic perovskite solar cells (MPSCs) based on mp‐TiO₂/mp‐ZrO₂/carbon triple mesoscopic layers are competitive candidates among various rapidly developed PSCs for future photovoltaic applications due to the characteristics of low‐cost, easy upscaling, and superior stability. However, the open‐circuit voltage (V _OC) loss in printable MPSCs is relatively large compared to that in conventional PSCs, deteriorating the power conversion efficiency (PCE). Herein, the V _OC loss is reduced by the octyltrimethylammonium chloride (OTAC) additive. OTAC is found to upshift the Fermi level of TiO₂ and passivate trap states in bulk MAPbI₃ perovskite, thus optimizing the energy‐level alignment of the TiO₂/perovskite heterojunction and suppressing nonradiative recombination in devices. As a result, MPSCs deliver the highest PCE of 16.53% with an improved V _OC of 1007 mV. The work demonstrates a facile strategy to reduce the V _OC loss in printable MPSCs by simultaneously optimizing the energy‐level alignment and suppressing nonradiative recombination.

This work presents effective grain boundary defect passivation in a 1.78 eV quadruple cation wide‐bandgap perovskite using a combination of two approaches for passivation: four cations (RbCsFAMA) and secondary growth (by guanidinium iodide) to achieve high efficiency.

Development of high‐performance wide‐bandgap perovskites is a key component to enable tandem solar cells with either a silicon or low‐bandgap perovskites. However, the presence of defects in the Br‐rich wide‐bandgap perovskites, especially in the grain boundaries (GBs) has been particularly challenging and limits its performance. Herein, to accomplish the passivation of these defects, a combination of cation management with rubidium (Rb) introduction into the triple cation combination of cesium/formamidinium/methylammonium (CsFAMA) is exercised. Passivation is further enhanced by secondary growth (SG) using guanidinium iodide. In‐depth assessments of GB defect passivation are performed using Kelvin probe force microscopy (KPFM) and nanoscale charge‐carrier dynamics mappings provide insightful details on the presence of GBs defects and their suppression by the cation management and SG techniques. Reduction of unreacted PbX₂ to realize a highly crystalline perovskite surface is achieved after incorporating Rb and SG treatment. As a result, a champion cell for 1.78 eV (FA_0.79MA_0.16Cs_0.05)_0.95Rb_0.05Pb(I_0.6Br_0.4)₃ wide‐bandgap perovskite with an efficiency of 17.71% along with enhancement in all photovoltaic parameters is achieved. This study introduces a new way to analyze GB defects and reveals the consequence of defect passivation on charge‐carrier dynamics for realizing efficient perovskites.

In situ diagnostics (X‐ray scattering and optical absorbance) reveal nearly identical crystallization behaviors of all MAPbBr_{3− x} Cl _x perovskite alloys and pure halide systems from a dimethyl sulfoxide (DMSO) solution, which is vastly different from methylammonium lead iodide (MAPbI₃). The similarities in the structure and the phase transformation pathway promote halide homogeneity in the mixed‐halide perovskite alloys.

The current understanding of the crystallization, morphology evolution, and phase stability of wide‐bandgap hybrid perovskite thin films is very limited, as much of the community's focus is on lower bandgap systems. Herein, the crystallization behavior and film formation of a wide and tunable bandgap MAPbBr_{3− x} Cl _x system are investigated, and its formation and phase stability are contrasted to the classical MAPbI_{3− x} Br _x case. A multiprobe in situ characterization approach consisting of synchrotron‐based grazing incidence wide‐angle X‐ray scattering and laboratory‐based time‐resolved UV–Vis absorbance measurements is utilized to show that all wide‐bandgap perovskite compositions of MAPbBr_{3− x} Cl _x studied (0 < x < 3) crystallize the same way: the perovskite phase forms directly from the colloidal sol state and forms a solid film in the cubic structure. This results in significantly improved alloying and phase stability of these compounds compared with MAPbI_{3− x} Br _x systems. The phase transformation pathway is direct and excludes solvated phases, in contrast to methylammonium lead iodide (MAPbI₃). The films benefit from antisolvent dripping to overcome the formation of discontinuous layers and enable device integration. Pin‐hole‐free MAPbBr_{3− x} Cl _x hybrid perovskite thin films with a tunable bandgap are, thus, integrated into working single‐junction solar cell devices and achieve a tunable open‐circuit voltage as high as 1.6 V.

Herein, the two‐step deposition of perovskite in mesoporous‐carbon‐based perovskite solar cells with repeatable power conversion efficiency over 12% is analyzed. Stability characterizations show degradation with time, however, a complete recovery of the devices in the dark was revealed. Analyzing the mechanism for this shows that the perovskite's unit cell shrinks during the recovery process due to internal stress relief.

Lead halide perovskites attract much attention in recent years as a realistic solution for efficient and low‐cost solar cells. One of the interesting solar cell structures is the fully mesoporous‐carbon‐based perovskite solar cells. The mesoporous layers can be fabricated entirely by screen printing with the potential for upscaling. Herein, the two‐step deposition of perovskite in mesoporous‐carbon‐based perovskite solar cells is studied. The influence of the dipping time on the photovoltaic parameters is investigated using charge extraction and intensity‐modulated photovoltage spectroscopy (IMVS) measurements. A power conversion efficiency of 15% is observed for cells fabricated using two‐step deposition which is one of the highest reported for this solar cell structure. Stability characterizations at maximum power point (MPP) tracking show degradation with time, however a complete recovery of the devices in the dark is revealed. Analyzing the mechanism for this shows that the perovskite's unit cell shrinks during the recovery process due to internal stress relief. This interesting phenomenon opens the possibility to optimize the stability of these solar cells for commercial applications.

With the proper extension of the backbone by inserting thiophene rings via single-bond connections, a Y6 derivative, i.e., BTPTT-4F-2T, is superior to prototype Y6 in key photovoltaic parameters, including the dipole moment, frontier molecular orbital energy, UV–vis absorption spectrum, singlet–triplet energy gap, exciton binding energy, charge transfer rate constant at the donor–acceptor interface, and electron mobility.

Recently, the application of the non-fullerene acceptor (NFA) Y6 and its derivatives has increased the power conversion efficiencies (PCEs) of organic solar cells (OSCs) up to 18.22%. It has opened up a new revolutionary direction of the molecular design of high-performance NFAs. Despite the recent exciting experimental progress of Y6-based OSCs, studies of molecular modifications of Y6, which may be the most effective way to improve the PCE of OSCs, are still few. Herein, a series of modified Y6 molecules is systematically designed and modeled. Their physical and optical properties are predicted with reliable density functional theory (DFT) and time-dependent DFT calculations. The dipole moments, frontier molecular orbital energies, UV–vis absorption spectra, singlet–triplet energy gaps, exciton binding energies, charge transfer rate constants at the donor–acceptor interface, and electron mobility are computed to comprehensively analyze the potential of these Y6 derivatives. The results show that proper extension of the backbone by inserting thiophene rings with a single-bond connection is conducive to designing highly efficient NFAs. The most striking finding here is that one (named BTPTT-4F-2T) of the screened Y6 derivatives is superior to prototype Y6 in all aspects and may be the next star high-performance NFA.

The deformation of bismuth bromide octahedra stimulated by lattice shrinkage enhances exciton–phonon coupling, resulting in bright blue emission at pressure of 4.9 GPa or low temperature for the Zero-dimensional (0D) organic–inorganic metal halide perovskite [(C₆H₁₁NH₃)₄BiBr₆]Br·CH₃CN (Cy₄BiBr₇ ). This research provides a new research approach for the acquisition of the high efficiency blue emitting materials.

Abstract

Understanding the structure–property relationships in Zero-dimensional (0D) organic–inorganic metal halide perovskites (OMHPs) is essential for their use in optoelectronic applications. Moreover, increasing the emission intensity, particularly for blue emission, is considerably a challenge. Here, intriguing pressure-induced emission (PIE) is successfully achieved from an initially nonluminous 0D OMHP [(C₆H₁₁NH₃)₄BiBr₆]Br·CH₃CN (Cy₄BiBr₇ ) upon compression. The emission intensity increases significantly, even reaching high-efficiency blue luminescence, as the external pressure is increased to 4.9 GPa. Analyses of the in situ high-pressure experiments and first-principle calculations indicate that the observed PIE can be attributed to the enhanced exciton binding energy associated with [BiBr₆]^3– octahedron distortion under pressure. This study of Cy₄BiBr₇ sheds light on the relationship between the structure and optical properties of OMHPs. The results may improve potential applications of such materials in the fields of pressure sensing and trademark security.

The fundamental reasons for efficient emission of halide perovskites are investigated, which is helpful to get efficient light emission of lead‐free halide perovskites. The synthesis, crystal structure, optical and optoelectronic properties of different molecular dimensional lead‐free halide perovskites with different forms are then systematically reviewed. Finally, the applications of light‐emitting devices (phosphor‐converted LEDs and electroluminescent LEDs) are discussed.

Abstract

Lead‐based halide perovskites have received great attention in light‐emitting applications due to their excellent properties, including high photoluminescence quantum yield (PLQY), tunable emission wavelength, and facile solution preparation. In spite of excellent characteristics, the presence of toxic element lead directly obstructs their further commercial development. Hence, exploiting lead‐free halide perovskite materials with superior properties is urgent and necessary. In this review, the deep‐seated reasons that benefit light emission for halide perovskites, which help to develop lead‐free halide perovskites with excellent performance, are first emphasized. Recent advances in lead‐free halide perovskite materials (single crystals, thin films, and nanocrystals with different dimensionalities) from synthesis, crystal structures, optical and optoelectronic properties to applications are then systematically summarized. In particular, phosphor‐converted LEDs and electroluminescent LEDs using lead‐free halide perovskites are fully examined. Ultimately, based on current development of lead‐free halide perovskites, the future directions of lead‐free halide perovskites in terms of materials and light‐emitting devices are discussed.

The methodology for optical modelling of perovskite light‐emitting diodes is investigated. Reabsorption in the perovskite causes divergence in classical methods of optical modelling. Here, the divergence is resolved by exploring the physical meaning of non‐radiative nearfield coupling to nearby emissive material. This enables the quantitative analysis of light emission in perovskites, including the contribution of photon recycling.

Abstract

Compared to organic emitters, perovskite materials generally have a small Stokes shift and correspondingly large re‐absorption of dipole emission. Classical optical modelling methods ignoring re‐absorption do not provide an adequate description of the observed light emission properties. Here, optical modelling methods and design rules for perovskite light‐emitting diodes are presented. The transfer‐matrix formalism is used to quantify the Poynting vectors generated by a dipole radiating inside a perovskite optoelectronic device. A strategy is presented to deal with non‐radiative coupling to nearby emissive material that can otherwise lead to non‐physical divergence in the calculation. Stability issues are also investigated regarding coherence of the light propagating in the substrate and the absence of a light absorber in the system. The benefit of the photon recycling effect is taken into account by recursive calculation of the dipole generation profile. The simulation results predict that a high external quantum efficiency of ≈40% is achievable in formamidinium lead triiodide‐based perovskite light‐emitting diodes, by optimization of microcavity, dipole orientation, and photon recycling effects. Contrary to conventional device structures currently reported, this work highlights the benefits of thick charge transport layers and thick perovskite with small Stokes shift.

Bismuth-based double perovskite Cs₂AgBiBr₆ is regarded as a potential candidate for low-toxicity, high-stability perovskite solar cells. However, its performance is far from satisfactory. Albeit being an indirect bandgap semiconductor, we observe bright emission with large bimolecular recombination coefficient (reaching 4.5 ± 0.1 x 10^–11 cm³ s^–1) and low charge carrier mobility (around 0.05 cm² s^–1 V^–1). Besides intermediate Fröhlich couplings present in both Pb-based perovskites and Cs₂AgBiBr₆, we uncover evidence of strong deformation potential by acoustic phonons in the latter through transient reflection, time-resolved terahertz measurements, and density functional theory calculations. The Fröhlich and deformation potentials synergistically lead to ultrafast self-trapping of free carriers forming polarons highly localized on a few units of the lattice within a few picoseconds, which also breaks down the electronic band picture, leading to efficient radiative recombination. The strong self-trapping in Cs₂AgBiBr₆ could impose intrinsic limitations for its application in photovoltaics.