Though perovskites remain a vital component of the electronics industry and solar cell technology, the defects that occur in perovskite films due to uncontrollable crystallization and the fragility of ionic compounds remain serious limitations. The present study focused on synthesising a perovskite Cs0.1MA0.9PbI3 active layer with tailored configurations using transition metal sulphides (both pure and V-doped WS2 and MoS2) to enhance the device characteristics of perovskite solar cells (PSCs). By optimizing the organic-inorganic interface, the power conversion efficiency (PCE) of the optimised V-doped WS2-based PSC increased by 48% to reach an impressive 15.62%, representing a significant improvement from pure Cs0.1MA0.9PbI3. This enhanced output originates from the high photon absorption capability of V-doped WS2 and the efficient low-dimensional charge transport pathways, which together effectively increase the generation, separation, and collection of charge while minimizing recombination losses. In long-term stability testing, the optimized device retained 80% and 76% of its PCE after 1000 h under continuous illumination and at 70 °C, respectively. The proposed V-doped MS2- and WS2-based design offers reliable interfacial energy alignment and enriched charge transport, while also exhibiting great promise for scalable processing, positioning it as a useful candidate for next-generation energy conversion technologies.

Perovskite light-emitting diodes (PeLEDs) are promising for display applications owing to their excellent color purity and efficiency. However, they often face the challenge of maintaining high efficiency at high luminance (>1000 cd m-2). The unintended formation of low-dimensional phases and defects during the crystallization of 3D perovskites is considered to be one of the detrimental factors limiting device performance. Here, we introduce an ionic liquid, tributyl(methyl)phosphonium dimethyl phosphate (TDP), into the precursor of a light-emitting bromide perovskite. This process is found to form perovskite emissive layers with suppressed low-dimensional phases, improved film morphology, and reduced defect density. The resultant green PeLEDs achieve peak external quantum efficiency (EQE) exceeding 20% at 1000 cd m-2, a high brightness of 3.7 × 105 cd m-2, and a T50 lifetime of 47 h at an initial luminance of 1000 cd m-2. Our work highlights the effectiveness of dimethyl phosphate ionic liquids in controlling the formation of 3D perovskites, contributing to the advancement of high-performance green PeLEDs.

The interfacial defect challenge between perovskite and electron transport layer (ETL) in inverted perovskite solar cells have become a critical bottleneck for achieving concurrent high efficiency and stability in the process of industrialization. We developed a novel multifunctional integrated polymer semiconductor material P4N-Cl as an interface interlayer between perovskite and [6,6]-phenyl-C61-butyric acid methyl ester. Various functional groups including carbonyl group, Cl atom and sp2-N atom in the polymer backbone effectively passivate defects at the perovskite interface through a synergistic coordination mechanism and significantly suppress non-radiative recombination losses. Simultaneously, the robust interfacial binding at the heterointerface further optimizes the energy level alignment at the perovskite/ETL interface and enhances charge carrier dynamics. The inverted PSCs based on the P4N-Cl multifunctional layer achieved a champion efficiency of 26.20% and a high open-circuit voltage of 1.21V. The target devices retained 96.2% and 90.2% of their initial power conversion efficiency after 2016h aging in ambient air (40%-60% relative humidity) and 1500h maximum power point tracking at 65°C under 1-sun illumination in nitrogen, respectively. This "one-stop" design provides exciting research prospects for constructing a new generation of commercially viable perovskite solar cells with high efficiency and long-term operation stability of devices.

Self-assembled monolayers based hole-transport layers (HTLs) have endowed inverted perovskite solar cells (PSCs) with dramatically improved photovoltaic performance and scalability. Their molecular ordering however affects the defect passivation in the perovskite buried interface and interfacial charge transfer. Herein, we propose an effective doping mixed SAMs strategy to modulate molecular ordering of SAMs, strengthen the interfacial interactions with perovskite buried surface, and mitigate tensile strain in the perovskite film. Leveraging the solubility and phase compatibility difference during solution-processing of mixed SAMs and perovskite layers, the dopant enriched on top of SAMs surface to form coordination bonding with the perovskite buried interface. The synergistic interfacial engineering enables 23.48% efficiency for 1.68eV bandgap inverted PSCs with over 90% retention after 1500h under 1-sun illumination. Moreover, the strategy was successfully extended to two-terminal monolithic perovskite/silicon tandem solar cells to afford impressive PCEs of 30.18%. Our doping mixed SAMs strategy demonstrates great efficacy for interfacial engineering of wide bandgap perovskite to fabricate efficient perovskite single-junction and tandem solar cells.

Two-dimensional (2D) and quasi-2D layered perovskites, composed of alternating spacer cations and inorganic layers, have emerged as promising alternatives to conventional three-dimensional (3D) perovskites due to their suppressed halide ion mobility and improved ambient stability. Nevertheless, both halide anion and spacer cation migration can still occur in these reduced-dimensional perovskites, and ion migration remains a critical challenge for perovskite optoelectronic applications. Under photoirradiation and electrochemical bias, intrinsic iodine electrochemistry drives defect-mediated halide ion migration, further promoting halide segregation in mixed halide systems. Several effective strategies have been proposed to mitigate such dynamic ion migration, including controlling the inorganic layer number (n), crystallographic phase (Ruddlesden-Popper or Dion-Jacobson), crystal orientation, and, most importantly, the molecular structure of the intercalated spacer cations. However, a mechanistic understanding that links these structural parameters (spacer, A-, B-, and X-site composition) to lattice stability and ion migration remains limited. The ion migration processes discussed in this review provide insights into the thermodynamic and kinetic factors governing ion migration and offer design principles for improving the long-term operational stability of perovskite-based devices.

Flexible all-perovskite tandem solar cells (PTSCs) are promising for lightweight photovoltaics, yet their mechanical degradation under bending remains poorly understood. Although bending instability has often been attributed to brittle fractures, halide perovskites are mechanically soft materials. Here, we demonstrate that bending-induced degradation in flexible PTSCs primarily associated with strain-induced evolution of residual-stress accumulation prior to crack formation, while elastic-modulus engineering through grain-boundary polymerization mitigates this mechanically induced degradation. Grazing-incidence X-ray diffraction analyses reveal that repeated bending accumulates residual stress of both wide-bandgap and narrow-bandgap perovskite layers in PTSCs, leading to fatigue-associated degradation and enhanced nonradiative recombination even in the absence of visible cracks. To address this intrinsic limitation, a dual-layer grain-boundary in situ polymerization strategy is introduced for both perovskite layers, enabling elastic relaxation and suppressing residual-stress accumulation. As a result, flexible PTSCs achieve a power conversion efficiency of 24.97% and retain over 90% of their initial efficiency after 5000 bending cycles at a radius of 5 mm. This work establishes elastic-modulus engineering as a key design principle for mechanically robust flexible perovskite tandem solar cells.

Efficient hole-transporting materials (HTMs) are crucial for improving the power conversion efficiency (PCE) and operational stability of perovskite solar cells (PSCs). Nevertheless, the rational design of organic HTMs that simultaneously combine suitable energy-level alignment, visible transparency, good chemical stability, facile film formation, and efficient hole-transport characteristics remains a major challenge. In this work, first-principles calculations were employed to investigate the structural, optical, electrochemical, solubility, chemical stability, and charge-transport properties of five spirofluorenedithiolane-based derivatives (SFT1-SFT5), designed through thiophene-bridged end-capped acceptor engineering of the parent SFT-STPA molecule. The designed HTMs exhibit suitable frontier orbital alignment with the perovskite absorber, indicating favorable hole extraction and transport. Their highest occupied molecular orbitals (HOMO) energies range from - 5.15 to -5.26eV, indicating improved stabilization relative to the reference molecule (-5.07eV). Moreover, the designed derivatives retain absorption maxima below 470nm, which helps minimize parasitic absorption and preserve effective light harvesting by the perovskite layer. Reduced reorganization energies (0.3032-0.3933eV), higher hole-transfer integrals (0.1250-0.1690eV), and rapid hole-transfer rates collectively indicate favorable hole-transport behavior. In addition, more favorable solvation free energies (-56.84 to -47.92kcal mol- 1) suggest improved processability and film-forming ability. Overall, these results identify spirofluorenedithiolane-based derivatives as promising HTM candidates for high-performance PSCs.

This work investigates the optical stability of formamidinium-cesium lead halide perovskite thin films deposited on fluorine-doped tin oxide substrates and aged under ambient conditions for 21 days. The optical response was analyzed through specular and diffuse transmittance and reflectance measurements, collected with light incident from both sides of the heterostructure. Specular transmittance exhibits nonmonotonic variations with an initial increase followed by a gradual decrease over time, while diffuse transmittance increases systematically across the full spectral range, indicating the progressive formation of scattering centers. Total reflectance decreases monotonically with aging, revealing that degradation is primarily governed by absorption-related optical losses. Despite these changes, the absorption edge remains stable, and the optical bandgap and Urbach tail show no significant variation. Direction-dependent measurements demonstrate that the fluorine-doped tin oxide substrate is the dominant source of initial scattering whereas the perovskite layer initially reduces optical contrast and later introduces disorder as degradation progresses. Haze values remain nearly constant over time, indicating that changes in scattering efficiency are moderate compared to absorption losses. These results demonstrate that integrating sphere-based optical spectroscopy provides a nondestructive and effective framework for monitoring early stage degradation in perovskite thin films.

Interfacial defects and ion migration critically limit the efficiency and operational stability of perovskite solar cells (PSCs), particularly under low-light conditions where interfacial recombination dominates. Herein, a postsurface treatment using the secondary amine dibutylammonium bromide (DBABr) is introduced to induce controlled 2D/3D interfacial reconstruction through the formation of a thin quasi-two-dimensional perovskite layer on a three-dimensional absorber. This dimensionally reconstructed interface effectively passivates surface defects, suppresses ion migration, and improves energy-level alignment without hindering charge extraction while remaining compatible with both organic and inorganic hole-transport layers (HTL). Under standard one-sun illumination (AM 1.5G), DBABr-treated devices exhibit a significant enhancement in power conversion efficiency (PCE), increasing from 13.82% to 15.52% relative to the control. Furthermore, the reconstructed interface enables efficient indoor energy harvesting, delivering a PCE of 30.57% for 0.09 cm2 active-area devices and improving the PCE from 25.64% to 27.77% for 1 cm2 devices under 1000 lx LED illumination, demonstrating scalability across device areas. Benefiting from the combined effects of the hydrophobic 2D surface layer and the carbon electrode, the devices retain approximately 90% of their initial efficiency after 1000 h of operation under ambient conditions. These results establish interfacial dimensional reconstruction via secondary-amine surface engineering as an effective strategy to simultaneously enhance efficiency, low-light performance, and operational durability of carbon-based PSCs, contributing to sustainable photovoltaic technologies aligned with Sustainable Development Goal 7 (affordable and clean energy).

Scalable manufacturing of high-efficiency perovskite solar cells (PSCs) requires blade coating not only of the perovskite layer, but also of other functional layers, including organoammonium halide surface passivation layers and self-assembled monolayers (SAMs), under ambient conditions. However, organoammonium iodides and SAMs are highly hygroscopic and prone to hydrolysis and desorption, respectively, and they are commonly processed from hygroscopic alcohol. As a result, despite its importance for scalable production, ambient blade coating of these moisture-sensitive interfacial layers has rarely been demonstrated. Here, we report a general low-hygroscopic solvent system for blade coating hygroscopic organoammonium halides and SAMs. We mix alcohol with low-polarity alkane, where the alcohol dissolves the functional materials and the alkane suppresses moisture uptake during the blade-coating process under ambient conditions. Comprehensive chemical and optoelectronic characterizations confirm that low-hygroscopic solvent system is a general approach to blade coat both passivation layers and SAMs under high humidity. The devices with air blade-coated SAMs, perovskite, and passivation layers achieve a certified efficiency of 26.1% with negligible decrease even fabricated at 80% relative humidity. This work solves one of the most challenging issues of scalable fabrication of perovskite photovoltaics in ambient air.

Flexible perovskite solar cells (F-PSCs) offer a compelling solution to the intrinsic rigidity of silicon-based photovoltaics, enabling power generation on irregular surfaces. However, their practical application hinges on the perovskite layer's ability to concurrent thermal cycling, so as to match the deformability of polymer substrates. Different from the conventional lattice solidification strategy for rigid devices, we incorporate a fluorinated misplaced-dipole engineered repairable elastomer into the perovskite film, which enhances perovskite intergranular toughness and mitigates thermal stress fatigue cracks. The resultant perovskite film exhibits suppressed lattice thermal fluctuation, thereby boosting enhanced environmental resilience. Consequently, the optimized F-PSCs deliver a champion efficiency of 25.54%, versus 26.83% for their rigid counterparts. More importantly, the F-PSC demonstrates exceptional durability under harsh operational stresses, retaining over 90% of the initial PCE after 11,000 bending cycles and maintaining a comparable retention rate following 500 thermal cycles, paving the way towards for the long-lasting flexible photovoltaic devices.

Interface passivation is crucial to reduce nonradiative recombination losses at the perovskite-electron transport layer interface and enhance the power conversion efficiency (PCE) of perovskite solar cells. Various molecules are known to result in a gain in open-circuit voltage (VOC). However, this gain is often associated with increased instability. Here, we investigate the interface passivation of a Cs0.1FA0.6MA0.3Pb0.5Sn0.5I3 narrow-bandgap (1.26 eV) perovskite by ammonium iodide derivatives with multiple, primary, secondary, or tertiary ammonium iodide groups, connected via alkane linkers of different lengths to establish structure-property relationships. The impact of these passivators on interfacial recombination, charge extraction, and device stability is elucidated by tracking the quasi-Fermi level splitting (QFLS) of perovskite layers and perovskite/C60 bilayers, together with the VOC of complete solar cell devices over one month. All tested passivators reduce the nonradiative recombination losses at the perovskite/C60 interface, but the extent to which this translates into an improved photovoltaic performance strongly depends on the molecular structure. Short-chain primary diammonium passivators provide the most favorable balance between effective passivation and charge extraction, yielding QFLS values that closely match the device VOC. In contrast, extended and branched multiammonium passivators improve photovoltage stability but impede charge carrier extraction, leading to reduced fill factors (FF) and short-circuit current densities (JSC). Secondary ammonium terminal groups promote crystallite formation on the perovskite surface, which reduces the efficacy of passivation. Importantly, combining small with larger-sized passivators in a single layer enables simultaneous enhancement of QFLS, VOC, FF, and operational stability.

The performance of inverted perovskite solar cells (PSCs) is critically constrained by interfacial losses arising from the insufficient coverage and weak adhesion of self-assembled monolayers (SAM). Herein, we report a SAM regulation strategy by mixing hydroxylated V2CTx MXene (V2C-OH) with nickel oxide (NiOx), which can provide abundant hydroxyl sites for SAM anchoring, thereby forming a uniform and dense SAM layer. First-principles calculations further reveal that the binding energy between SAM and hydroxyl groups on V2C-OH is stronger than that on pristine NiOx, explaining the enhanced thermal stability of SAM on the hybrid substrate. Meanwhile, the highly ordered and tightly packed SAM layer promotes vertical growth and [001]-preferred orientation of perovskite grains. Therefore, the introduction of V2C-OH enables a top-down modulation of the NiOx, SAM, and perovskite layers, improving their morphology and interfacial properties. The resulting PSCs achieve a champion power conversion efficiency of 26.6% (certified at 26.2%) for a 0.0524 cm2 device and 24.7% for a 1 cm2 device, along with outstanding long-term operational stability.

ABSTRACT With power conversion efficiencies exceeding 27%, metal halide perovskite (PK) solar cells are among the most promising next‐generation photovoltaic technologies. Yet, their large‐scale deployment remains limited by instability under light, heat, and humidity. This study introduces a scalable stabilization strategy combining carbon‐based mesoscopic architectures based on MA 1− x (AVA) x PbI 3 perovskite and CsPbBr 3 quantum dots (QDs) to simultaneously enhance durability and performance. All devices were fabricated under ambient conditions and evaluated following standardized ISOS protocols (ISOS‐D‐3, 85°C/85% RH; ISOS‐L‐1(SC), 1 SUN). Integrating QDs into the perovskite layer improved both spectral management and intrinsic stability, reducing degradation rates under damp‐heat and illumination stress. Devices incorporating short‐chain‐ligand QDs showed superior resistance to humidity and temperature, with performance losses below 5% after aging. Under continuous illumination, QD‐modified cells exhibited self‐healing behavior, recovering most of their initial efficiency after dark storage. Comparative analysis reveals that damp‐heat exposure induces irreversible chemical and interfacial degradation, whereas photo‐stress leads mainly to reversible interface effects mitigated by QDs. These results demonstrate the dual role of QDs in defect passivation and dynamic recovery, establishing a new framework for designing scalable, stable perovskite–QD heterostructures that meet industrial requirements for long‐term reliability.

Perovskite solar cells (PSCs) are highly attractive for space applications due to their high power-to-weight ratio, yet their reliability under extreme thermal environments remains unclear. Here we investigate interfacial stability in devices employing polymeric PTAA, self-assembled monolayer MeO-2PACz, and a sequential PTAA/MeO-2PACz bilayer. Devices were evaluated under space-relevant conditions, including vacuum, AM0 illumination and thermal cycling spanning −40 °C to 90 °C. While MoO-2PACz enables high efficiency through interfacial engineering, it exhibits severe degradation under thermal tress due to thermomechanical mismatch with the perovskite layer, leading to interfacial defects and phase instability. In contrast, PTAA provides improved thermal stability but lower efficiency. The bilayer structure achieves both high efficiency and enhanced durability, retaining 73% of its initial performance after thermal cycling. This improvement arises from the polymeric layer mitigating thermomechanical stress and suppressing δ-phase transitions. These results suggest efficient interfacial thermomechanical engineering and strategy to thermal durability in PSCs for harsh space environments.

The performance of inverted perovskite solar cells (PSCs) is often impeded by severe non-radiative recombination and carrier transport losses at the self-assembled monolayer (SAM)/perovskite interface, arising from inhomogeneous SAM distribution and weak interfacial bonding with the perovskite layer. To address these challenges, we introduce a universal synergistic interface engineering strategy employing 2-aminopyrimidine-4-carboxylic acid (m-APCA), a meta-substituted molecule featuring asymmetric bifunctional groups on its pyrimidine ring. These groups induce substantial molecular polarization, amplifying the dipole moment and reinforcing intermolecular π-π interactions with SAMs, thereby mitigating SAM aggregation and ensuring uniform substrate coverage. Concurrently, the strong dipole field and bifunctional chemistry of m-APCA enable robust chemical bonding with the perovskite layer, acting as nucleation sites that regulate grain growth and passivate buried interfacial defects. This dual-action approach reduces interfacial energy barriers and enhances hole transport efficiency, achieving very high efficiencies of 26.77% (certified at 26.71%), 26.08%, and 24.17% for small-area (normal bandgap), centimeter-scale (normal bandgap), and wide-bandgap PSCs, respectively. Notably, optimized PSCs demonstrate exceptional operational stability, retaining 96% of initial efficiency after 1200h of continuous maximum power point tracking.

Owing to their unique molecular structures and outstanding optoelectronic properties, self-assembled monolayers (SAMs) hold enormous promise as hole-transport materials for p-i-n structured inorganic perovskite solar cells (IPSCs). However, weak interfacial adhesion and molecular aggregation lead to insufficient coating and easy peeling from the substrate, limiting the power conversion efficiency (PCE) and operational stability of IPSCs. This work employs KOH to deprotonate the ─PO3H2 of [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) (2PACz-K), generating negatively charged ions, whose electrostatic repulsion suppresses intermolecular agglomeration, thereby forming a uniformly covered SAMs film. Meanwhile, 2PACz-K strengthens the binding interaction with the NiOx substrate and generates robust chemical linkages, which effectively suppress interfacial separation and non-radiative recombination. Thus, in contrast to the control devices (15.13%), the inverted CsPbI2Br IPSCs based on 2PACz-K delivered an optimal efficiency of 17.21% accompanied by a 1.326V open-circuit voltage (VOC), ranking among the highest values ever reported for such devices. Moreover, the deprotonated 2PACz-K alleviates acid-related corrosion toward the perovskite layer and passivates perovskite crystallites via K+ occupation at A-site defects. Under continuous maximum power point tracking (MPPT) at 85°C, devices incorporating 2PACz-K retained 80% of their initial performance over 710h.

Perovskite solar cells (PvSCs) are promising next-generation photovoltaic devices due to their high efficiency and low fabrication cost. Indium tin oxide (ITO), used as a transparent electrode in solar cells, significantly impacts device performance, however, its thickness is unaccounted for due to standardised commercial availability. This study systematically investigates the role of ITO thickness in planarn-i-pperovskite solar cells using a combined opto-electrical simulation. Different ITO thicknesses (70, 100, 150, and 190 nm) were analysed to understand and explore thickness dependent optical interference and dissipative absorptions, and their resultant effect on carrier generation, charge transport, and overall device performance. Optical simulations using the transfer-matrix method show that constructive interference builds up at intermediate ITO thicknesses (100-150 nm), which in turn enhances the visible-light transmission and increases light absorption within the perovskite layer. Electrical simulations confirm the results of optical simulations, which yield higher short-circuit current density, improved fill factor, and reduced resistive losses. Devices with 150 nm ITO exhibit the highest short circuit current density of 21.42 mA cm-2and power conversion efficiency (PCE) of 22.67%, while those with 70 and 100 nm show short-circuit current density of 21.21 mA cm-2and 21.25 mA cm-2withPCEof 22.90% and 23.23% respectively, presenting a promising cost-efficient guidance to researchers without much compromise in the performance. This study exemplifies that ITO thickness is a critical, still underexplored design parameter, and its optimisation provides a guiding route for achieving high efficiency of photovoltaic devices, while reducing material costs for next-generation photovoltaics.

All-perovskite tandem solar cells (TSCs) constructed by wide-bandgap (WBG) and narrow-bandgap (NBG) perovskites represent promising future to exceed the Shockley-Queisser limit due to the differential absorption of spectrum. However, the WBG perovskite sub cell suffers from substantial open-circuit voltage (VOC) losses and poor photovoltage performance caused by the severe phase segregation in the bulk, high defects density and non-radiative recombination losses at the buried interface. Herein, this work introduces a buried interfacial engineering by inserting N-Benzoyl-(2R,3S)-3-phenylisoserine (NBP) molecule between [4-(3,6-dimethyl-9H-carbazol-9-yl) butyl] phosphonic acid (Me-4PACz) and WBG perovskite layer, which simultaneously enhances film quality and energy level alignment. Additionally, experimental investigations demonstrate that the C═O and N─H groups in NBP exhibit significant effects in fixing uncoordinated Pb2+ ions and passivating iodide vacancies, suppresses halide phase segregation and reduces defect state density at the buried interface. Eventually, NBP-modified WBG PSCs achieved a power conversion efficiency (PCE) of 20.81% with VOC of 1.371V. Notably, the device exhibited exceptional photostability, retaining 85.3% of its initial PCE after 1000h of maximum power point tracking (MPPT). Moreover, integrating the NBP-modified WBG sub cell with 1.25eV NBG sub cell obtains a two-terminal (2T) TSCs with an impressive PCE of 29.05%.

Perovskite solar cells (PSCs) have rapidly evolved into next-generation photovoltaic devices because of their fascinating power conversion efficiencies and low manufacturing costs. However, achieving peak performance requires precise engineering of the electron transport layer (ETL) to optimise charge extraction and suppress recombination. Doping rare-earth (RE) into SnO2 is one potential way to enhance ETL properties and has been extensively studied1. In this study, we utilize SCAPS-1D simulations to investigate the impact of rare-earth (RE) doping (La, Ce, and Eu) in SnO2 ETLs within a FAPbI3-based PSC architecture. While variations in thickness and donor density of the perovskite layer were examined, our results reveal that device performance is primarily governed by bandgap engineering induced by the Burstein-Moss effect. This doping-induced bandgap widening shifts the conduction band edge, facilitating a quasi-ohmic contact and superior band alignment with the FAPbI3 absorber. At high defect densities and thicker absorber layer, however, a performance crossover was observed, highlighting the sensitivity of optimized interfaces to severe Fermi-level pinning. Motivated by this findings, we systematically optimized the perovskite absorber thickness and defect density (Nt), identifying a critical sweet spot at 0.6 μm and 1014 cm-3, respectively, where photon harvesting and bulk recombination are balanced. Notably, La-doped SnO2 exhibited the highest tolerance to bulk defects, maintaining superior Voc and FF through enhanced extraction kinetics that outrun trap-assisted recombination. Under optimized conditions, the La-doped device emerged as the champion configuration, significantly outperforming pristine device and marginally better than Ce-, and Eu-doped variants. These findings provide a fundamental framework for leveraging RE-doping to engineer interfacial energy levels, offering a clear pathway for the development of high-efficiency, defect-tolerant perovskite photovoltaics.