Ligang Yuan

The spontaneous black‐to‐yellow phase transition of cesium lead halides (CsPbX₃) after long‐time storage hinders their development in solar cells despite ever‐growing efficiencies. This review focuses on the current advances from recognizing phase transition behaviors to addressing phase instability issue of CsPbX₃ and provides potential avenues for further enhancing stability of CsPbX₃ based on current understandings.

Cesium lead halide (CsPbX₃) perovskite solar cells have gained considerable attention for their rapid evolution to over 19% power conversion efficiency. Despite high chemical stability, the spontaneous phase transition from desired black phase to nonperovskite yellow phase after long‐time storage or under attack of extrinsic factors significantly hinders their development and application. This review summarizes the current advances in recognizing phase transition behaviors of cesium lead halides, especially cesium lead tri‐iodide, and addressing phase instability issues. Advancing strategies that are used for phase stabilization, including compositional engineering, grain size reduction, modification of surface termination, and strain engineering, are highlighted as well as their present limitations. Also, existing scientific debates on phase transition and stability, origin of these arguments, and possible solutions are presented and discussed. Finally, some potential avenues for further enhancing stability of cesium lead halides are proposed based on current understandings.

The defect landscape in metal–halide perovskites is described. This Review highlights the promise of the compounds, explains defects as an outstanding problem, and discusses the background of defects, methods to probe defects, and various passivation strategies used successfully to date.

The rise of hybrid metal–halide perovskites as potential solar energy materials has revolutionized research on next‐generation solar cells. According to recent studies, the rationale behind such success is the rich defect physics of materials. Studies on the origin of different types of prevailing defects, their formation, and mechanism of defect passivation have hence become decisive avenues. Herein, the possible origins of defects and different defect analysis techniques in hybrid halide perovskites are discussed. While initiating the discussion with the archetypal methylammonium lead halide, perovskites beyond the conventional ABX₃ structure are included. In this direction, some major advancements to date on defect formation in the bulk of hybrid halide perovskites, at the grains and grain boundaries, are summarized. Numerous effective methods to passivate the defects and the adverse effect of defects on device efficiency are further highlighted. Hence, the prospect of defect engineering in perovskite materials is pointed toward improving the power conversion efficiency and long‐term stability of perovskite solar cells (PSCs). The discussion rightfully addresses that the in‐depth exploration of defect engineering is anticipated to have a gigantic impact toward the achievement of predicted efficiency in metal–halide PSCs.

Utilizing NP‐SC₆‐TiOPc and NP‐SC₆‐ZnPc as passivating agents on perovskite thin film through an antisolvent, improved performance and stability are achieved for perovskite solar cells. The highest power conversion efficiencies (PCEs) of 19.39% and 18.04% are obtained for NP‐SC₆‐TiOPc and NP‐SC₆‐ZnPc passivated devices, which is higher than that of the control devices without post‐treating the MAPbI₃ films (PCE of 17.67%).

Abstract

Semiconducting molecules have been employed to passivate traps extant in the perovskite film for enhancement of perovskite solar cells (PSCs) efficiency and stability. A molecular design strategy to passivate the defects both on the surface and interior of the CH₃NH₃PbI₃ perovskite layer, using two phthalocyanine (Pc) molecules (NP‐SC₆‐ZnPc and NP‐SC₆‐TiOPc) is demonstrated. The presence of lone electron pairs on S, N, and O atoms of the Pc molecular structures provides the opportunity for Lewis acid–base interactions with under‐coordinated Pb²⁺ sites, leading to efficient defect passivation of the perovskite layer. The tendency of both NP‐SC₆‐ZnPc and NP‐SC₆‐TiOPc to relax on the PbI₂ terminated surface of the perovskite layer is also studied using density functional theory (DFT) calculations. The morphology of the perovskite layer is improved due to employing the Pc passivation strategy, resulting in high‐quality thin films with a dense and compact structure and lower surface roughness. Using NP‐SC₆‐ZnPc and NP‐SC₆‐TiOPc as passivating agents, it is observed considerably enhanced power conversion efficiencies (PCEs), from 17.67% for the PSCs based on the pristine perovskite film to 19.39% for NP‐SC₆‐TiOPc passivated devices. Moreover, PSCs fabricated based on the Pc passivation method present a remarkable stability under conditions of high moisture and temperature levels.

A multifunctional triple‐layer system containing TiO₂/SiO₂/CeO₂ porous materials is numerically simulated and experimentally used on the glass side of hole transport layer–free carbon‐based perovskite solar cells. This strategy is designed to increase cell efficiency by enhancing the antireflective feature and long‐term stability via UV light blocking and superhydrophobic properties introduced to the surface.

Low‐cost carbon‐based perovskite solar cells (C‐PSCs) without a hole transport layer (HTL) and metal contact are highly promising for marketing. However, lower efficiency than conventional PSCs and instability during the penetration of moisture through the porous carbon electrode as well as the incoming of ultraviolet (UV) light from the glass side of the device remain challenges. Herein, a multifunctional triple‐layer system containing TiO₂/SiO₂/CeO₂ porous nanomaterials is numerically simulated and experimentally used on the glass side of HTL‐free C‐PSCs. This strategy is designed to increase cell efficiency by enhancing the antireflective feature and long‐term stability via the UV light blocking and superhydrophobic properties introduced to the surface. Furthermore, this system is durable against environmental pollutants due to the photocatalytic self‐cleaning effect of TiO₂. A superhydrophobic carbon back contact is also used to sandwich the perovskite active layer between two superhydrophobic surfaces and further the humidity resilience of the device. The device with polydimethylsiloxane (PDMS)–TiO₂/SiO₂/CeO₂/glass/meso‐TiO₂/MAPbI₃/superhydrophobic‐carbon configuration shows an efficiency of 16.60% among the HTL‐free C‐PSCs and superior long‐term stability (maintaining 98.5% of the initial efficiency without encapsulation) against UV light and relative humidity of 90% at 50 °C.

An interfacial layer of triphenylamine–polystyrene blend is used between the perovskite layer and charge‐transporting layer to concurrently suppress energy loss and improve device stability. The energy loss is reduced from 0.49 to 0.35 eV, along with a large open‐circuit voltage of 1.18 V and a high power conversion efficiency of 22.1% in air‐stable perovskite solar cells.

Energy loss induced by nonradiative recombinations plays a critical role in determining power conversion efficiencies in perovskite solar cells, whereas device stability impacts their long‐time reliability in the ambient environment. It is an important challenge to suppress energy loss and improve device stability simultaneously. Herein, an interfacial layer of triphenylamine (TPA):polystyrene (PS) blend coated on the hybrid perovskite layer to concurrently suppress energy loss and improve device stability is reported. The energy loss is suppressed from 0.49 to 0.35 eV by passivating surface defects in hybrid perovskites via Lewis acid–base interactions with the combination of electron‐donating aromatic nucleus in PS and tertiary amine in TPA, leading to perovskite solar cells with a high open‐circuit voltage of 1.18 V, a fill factor of about 80%, and a power conversion efficiency of 22.1%. Meanwhile, the device stability in the ambient environment is improved significantly by the TPA:PS blend due to its superior hydrophobicity which is suggested by its high contact angle of 91.1° as compared to 64.0° for the pristine perovskite film. Herein, an efficient interfacial engineering approach with the TPA:PS blend to suppress energy loss and improve device stability simultaneously towards realistic applications is demonstrated.

Bearing high hole mobility and appropriate energy levels, an organic small molecule 2,7‐bis(4‐octylphenyl)naphtho[2,1‐b:6,5‐b 0] difuran (C₈‐DPNDF) is introduced as a dopant‐free hole transporting material in inverted perovskite solar cells. The device with C₈‐DPNDF as HTM shows a decent power conversion efficiency of 17.5% and can keep 92% of its initial value after 30 days in ambient air.

Hole transport material (HTM) is a significant constituent in perovskite solar cells (PSCs). However, HTM generally is not utilized in its pristine form but with dopants (such as lithium salt, tert‐butyl pyridine, F₄‐TCNQ), which accelerates device degradation and leads to poor stability. Therefore, dopant‐free HTM is highly desirable to fabricate stable devices. Herein, a fused furan organic small molecule (C₈‐DPNDF) is introduced as a dopant‐free HTM in inverted PSCs. As a potential HTM candidate, C₈‐DPNDF shows excellent properties, such as high hole mobility, matched energy level with perovskite, and resistance to perovskite precursor solution. As a result, the device based on C₈‐DPNDF as HTM shows a power conversion efficiency (PCE) of 17.5%, compared with 17.1% of the control device based on classic poly(bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine) (PTAA) as the HTM. In addition, the unencapsulated device based on C₈‐DPNDF as HTM keeps 92% of its initial PCE after 30 days of storage in ambient air with a relative humidity of ≈40%. This finding is expected to pave the way toward stable and highly efficient inverted PSCs based on dopant‐free HTMs.

Due to the poor morphology and crystallinity of Sn–Pb mixed perovskites, it is found that the addition of potassium thiocyanate (KSCN) can effectively reduce the bulk defects and carrier recombination through optimizing the process of film formation and the perovskite film quality. Therefore, a whole improvement of device performance can be achieved under the optimization effect of KSCN doping.

The organic–inorganic Sn–Pb mixed perovskite has achieved great progress during the last 10 years and is considered as one of the most promising low‐bandgap photovoltaic materials. It has lower toxicity, outstanding optoelectrical properties, and achieved remarkable performance. However, there are still plenty of challenges in controlling the morphology, crystallinity, and defects of the Sn–Pb mixed perovskite film because of the inferior chemical stability of Sn compared with Pb. Herein, it is found that the synergistic effect of potassium thiocyanate (KSCN) in the Sn–Pb mixed perovskites can enlarge the grain size, enhance the crystallization, improve the film morphology, and obtain high‐quality perovskite films which effectively eliminate the bulk defects and smooth carrier transportation of Sn–Pb mixed perovskite solar cells. Through optimizing the concentration of KSCN, a high‐performance MA_0.5FA_0.5Pb_0.5Sn_0.5I₃ solar cell with an efficiency of 15.14% and improved stability is obtained. This work lays a key foundation for the fabrication of efficient and stable Sn‐based or Sn–Pb mixed perovskite solar devices.

The roles of small alkali metals on the stability of Sn perovskites are investigated by theoretical calculations and controlled experiments. K⁺ incorporation can enhance the Sn‐based perovskites by reducing structural instability and unintentional hole doping.

Sn‐based halide perovskites are the most promising alternatives for developing Pb‐free perovskite solar cell materials. However, the stability of Sn halide perovskites is the biggest concern for future developments. The phase stability and the doping‐level control should be resolved for Sn perovskites to compete with Pb‐based analogs. Herein, interstitial engineering is used to enhance the stability of Sn‐based halide perovskites using alkali metals through ab initio calculations and controlled experiments. This study reveals that alkali metal interstitials can promote the performance of Sn perovskites by controlling their phase stability, suppressing free carrier density, and locking lattice vibration. K⁺ shows the most promising behavior among alkali–metal cations in terms of phase stabilization and defect formation energy.

Carbon nanotube electrode–laminated perovskite and n‐type tunnel oxide–passivated contact (TOPCon) silicon solar cells exhibit 24.42% efficiency when stacked in tandem. Both semitransparency and power conversion efficiency are important for top subcells of tandem solar cells. The carbon nanotube‐based perovskite solar cells demonstrate record high efficiency among the reported four‐terminal tandem solar cells while exhibiting good semitransparency.

Carbon nanotube electrode–laminated perovskite solar cells in combination with n‐type tunnel oxide–passivated contact silicon solar cells demonstrate a high power conversion efficiency (PCE) of 24.42% when stacked in tandem. This is compared with conventional indium tin oxide/MoO _x ‐deposited perovskite solar cells which give an efficiency of 22.35% when stacked in the same four‐terminal tandem system. Despite higher transmittance of the carbon nanotube electrode than that of the indium tin oxide/MoO _x in the infrared range, the carbon nanotube electrode‐laminated devices show lower transmittance in the same region due to the total internal reflection and scattering as evidenced by optical simulation. Yet, the exceptionally high PCE of the carbon nanotube electrode‐laminated semitransparent devices far exceeding than that of the indium tin oxide/MoO _x ‐deposited semitransparent top cell outweighs the effect of the optical transparency. Four types of silicon solar cells are compared as the bottom subcells, and the n‐type tunnel oxide‐passivated contact silicon solar cells are the best choice mainly due to their high absorption in the long‐wavelength region. The obtained 24.42% efficiency is one of the high PCEs among the reported four‐terminal perovskite–silicon solar cells, and this article is the first demonstration of the carbon nanotube electrode application in tandem solar cells.

Perovskite solar cells (PSCs) and mini‐modules (PSM) scaling‐up strategies based on the design of their active areas and geometrical shapes lead to relevant power conversion efficiency (PCE) improvements. Optimized thermally co‐evaporated PSM with 6.4 cm² active area and geometrical fill factor of ≈91% reach a PCE of 18.4% with just 0.7% absolute losses as compared to 40 times smaller PSCs.

Perovskite solar cells (PSCs) have emerged as a promising technology for next‐generation photovoltaics thanks to their high power‐conversion‐efficiency (PCE). Scaling up PSCs using industrially compatible processes is a key requirement to make them suitable for a variety of applications. Herein, large‐area PSCs and perovskite solar modules (PSMs) are developed based on co‐evaporated MAPbI₃ using optimized structures and active area designs to enhance PCEs and geometrical fill factors (GFFs). Small‐area co‐evaporated PSCs (0.16 cm²) achieve PCE over 19%. When the PSCs are scaled‐up, the thin films high quality allows them to maintain consistent V _oc and J _sc, while their fill factors (FF), which depend on the substrate sheet resistance, are substantially compromised. However, PSCs with active areas from 1.4 to 7 cm² show a substantially improved FF when rectangular designs with optimized length to width ratios are used. Reasoning these results in the PSM design with optimal subcell size and for specific dead areas, a 6.4 cm² PSM is demonstrated with a record 18.4% PCE and a GFF of ≈91%. Combining the high uniformity of the co‐evaporation deposition with active areas design, it is possible to scale up 40 times the PSCs with PCE losses smaller than 0.7% (absolute value).

Perovskite solar cells with the 2D passivation layer display excellent photovoltaic performance and superior stability via introducing hydrophobic alkyl molecules with polyfunctional groups.

The charges stuck in trap sites hinder charge transport and lead to V _oc below the radiative limit, which seriously restrict the performance and stability of organic–inorganic halide perovskite solar cells (PSCs). Chemical passivation is an effective method to reduce defects and suppress nonradiative recombination. Herein, a new passivation molecule l‐cysteine methyl ester hydrochloride (CME) with thiol and ester groups is designed to modify the interface between the perovskite layer and hole transport layer (HTL). It reveals that thiol possesses outstanding moisture resistance and ester suppresses nonradiative recombination by coordinating with undercoordinated Pb²⁺. Furthermore, the 2D modified layer at the grain boundaries and surface passivates surface defects and promotes hole extraction. As a result, the CME device achieves the highest PCE of 20.33% with an enhanced open‐circuit voltage (V _oc) of 1.11 V. Due to the barrier of highly hydrophobic 2D perovskites, the modified devices show excellent stability while exposed to humidity and high‐temperature environment. A facile and effective strategy to design organic molecular structures with polyfunctional groups to passivate trap‐assisted nonradiative recombination at the surface and grain boundaries is provided.

A mixed lead precursor of halide lead source and nonhalide lead source is used to enable a low‐temperature, two‐step sequential deposition method for FAPbI₃ perovskite in triple‐mesoscopic solar cells. A power conversion efficiency of 16.21% is achieved.

The evolution from the original methylammonium (MA)‐ to formamidinium (FA)‐dominated perovskite makes a crucial contribution to improve the photoelectric performance of perovskite solar cells (PSCs) in a decade. However, to obtain α‐FAPbI₃, annealing temperature above 100 °C is essential. In addition, it is still challenging to deposit a uniform and high‐quality FA‐based perovskite absorber in printable triple‐mesoscopic PSC due to the complicated mesoscopic structure. Herein, a low‐temperature, two‐step sequential deposition method is used for pure FAPbI₃ perovskite in printable triple‐mesoscopic PSC. By using different lead sources, the crystallization and morphology of lead iodide (PbI₂) are finely controlled, which modulates the crystallization and pore filling of perovskite in mesoscopic structure. The improved interface contact promotes the transfer of charge carrier from perovskite to TiO₂. With the further introduction of cesium bromide (CsBr) into lead precursor, a power conversion efficiency of 16.24% is achieved. This study provides a deeper understanding of the pore filling and crystallization for both PbI₂ and perovskite, and helps explore and optimize the deposition process of perovskite in mesoscopic structure.

Herein, a one‐step solution‐processing of [MA_0.9Cs_0.1Pb(I_0.6Br_0.4)₃] wide‐bandgap perovskite using phenylhydrazine iodide with amino groups to successfully passivate the trap density within grain boundaries and increase the perovskite grain size is demonstrated. The reinforced morphology and grain boundaries treatment considerably enhance the power conversion efficiency from 12.16% for pristine to 14.63% for the treated devices.

Due to the attraction of fabricating highly efficient tandem solar cells, wide‐bandgap perovskite solar cells (PSCs) have attracted substantial interest in recent years. However, polycrystalline perovskite thin‐films show the existence of trap states at grain boundaries which diminish the optoelectronic properties of the perovskite and thus remains a challenge. Here, a one‐step solution‐processing of [ MA0.9Cs0.1Pb(I0.6Br0.4)3] wide‐bandgap perovskite using phenylhydrazine iodide with amino groups is demonstrated to successfully passivate the trap density within grain boundaries and increase the perovskite grain size. The reinforced morphology and grain boundaries treatment considerably enhanced the power conversion efficiency (PCE) from 12.16% for pristine to 14.63% for the treated devices. This strategy can be easily adopted to other perovskites and help realize highly efficient perovskite solar cells.

The water‐stable, lead‐free, and tunable bandgap perovskites of DMASnI _x Br_3−x crystals are first used for photoenzyme catalysis in nicotinamide adenine dinucleotide (NADH) regeneration with nearly 100% yield and efficient formation of formic acid from CO₂ in aqueous media. The water‐stable mechanism on water interaction with the DMASnI _x Br_3−x perovskites is investigated by density functional theory (DFT) calculation.

The impressive optoelectronic performances of hybrid perovskites have attracted enormous interests. However, the moisture sensitivity of these materials hampers their practical applications. Herein, the lead‐free perovskites of DMASnI _x Br_3−x (DMA = CH₃NH₂CH₃ ⁺) crystals as photocatalysts for nicotinamide adenine dinucleotide (NADH) regeneration in aqueous solution are engineered. The very high NADH yield (≈100%) is achieved for all the DMASnI _x Br_3−x crystals with tunable bandgaps, which is further coupled with formate dehydrogenase for the production of 320 μM formic acid from CO₂. The density functional theory (DFT) calculations further shed light on the intrinsic water‐stable mechanism of DMASnI₃ perovskite, which is ascribed to the higher water surface adsorption energy, the higher water osmotic energy barrier, and the smaller intralayer spacing inside DMASnI₃ structures by comparing with Pb‐based counterpart. The work can provide new prospects for designing water‐stable hybrid perovskites and further broaden their photocatalytic and optoelectronic applications.

Current density–voltage (J–V) hysteresis in perovskite solar cells (PSCs) is a major challenge in this field. Herein, the possible origins and factors of J–V hysteresis behavior in PSCs are focused and the strategies to suppress the hysteresis are summarized. Finally, insights on the future development of the J–V hysteresis in PSCs are also provided.

The power conversion efficiency (PCE) of perovskite solar cells (PSCs) has exceeded 25%, showing great potential in the photovoltaic field. However, PSCs often show anomalous current density–voltage (J–V) hysteresis behavior in the forward and reverse scanning directions, which makes it impossible to accurately evaluate the performance of PSCs. Therefore, it is necessary to clearly understand the mechanism of hysteresis and suppress the hysteresis. Herein, the J–V hysteresis behavior in PSCs and strategies to suppress hysteresis is focused: first, the various factors that affect J–V hysteresis in PSCs are summarized. And the mechanism behind the various possible origins of hysteresis and the challenges encountered are explored. Then, the strategies to suppress or eliminate the hysteresis are summarized, including optimizing the perovskite light‐absorbing layer, improving the performance of the carrier transport layer and interface engineering. Finally, insights on the future development of the hysteresis are also provided.

B‐site doping provides a new approach to improve the optoelectronic properties and stability of CsPbX₃ inorganic perovskite. By judiciously selecting B‐site dopants and optimizing their concentration, B‐site doping strategy remarkably enhances the stability, tunes the bandgap, reduces the defects of CsPbX₃ inorganic perovskites, and thereby improves the photovoltaic performance of inorganic perovskite solar cells.

CsPbX₃ (X = I, Br) inorganic perovskite solar cells (PSCs) have been considered as one of the most appealing research topics in the fields of photovoltaic technologies in the past several years due to their excellent thermal stability and booming conversion efficiency. Nevertheless, there are still a large number of critical challenges and issues for inorganic PSCs, such as unstable phase structure of I‐rich inorganic perovskites at ambient condition, the wide bandgap of Br‐rich inorganic perovskites, and serious defect traps, hindering further development of inorganic PSCs. Recently, partially substituting Pb²⁺ with other metal ions has been shown to enhance the stability, tune the bandgap, reduce the defects of CsPbX₃ inorganic perovskites, and thereby improve the photovoltaic performance of inorganic PSCs. Herein, the recent progress in improving the photovoltaic performance of inorganic PSCs through the B‐site doping strategy is summarized, and the influence of the alternative metal ions on the stability and optoelectronic properties of inorganic perovskites and photovoltaic characteristics of CsPbX₃‐based PSCs is discussed. Finally, the issues that need to be understood in more detail are presented. It is believed that B‐site doping offers a practical strategy to gain high‐performance perovskite photovoltaic devices.

State‐of‐the‐art perovskite solar cells (PSCs) based on three‐dimensional (3D) films have achieved high power conversion efficiencies (PCEs), but are relatively fragile in high‐temperature and humid environments. This shortcoming must be addressed before PSCs can be fully commercialized. Here, we demonstrate the use of a fluorinated aromatic organic spacer cation, 4‐fluoro‐phenethylammonium iodide (FPEAI), to fine‐tune the dimensionality and surface morphology of perovskite films. The isosteric substitution of hydrogen by an electronegative fluorine atom enhances the moisture/thermal stability and polarization in the crystal lattice of FPEAI. Surface treatment with FPEAI can lead to in situ formation of a two‐dimensional (2D) FPEA₂PbI₄ perovskite capping layer atop a 3D perovskite film, producing novel 3D/2D interface in perovskite films. Simultaneously, FPEAI treatment can induce a novel grain‐boundary passivation effect on the film surface, which helps to suppress undesirable charge recombination. After FPEAI treatment, standard (0.09 cm²) and large‐area (2.00 cm²) PSCs achieved PCEs of 20.53% and 16.82%, respectively. The FPEAI‐treated PSCs also demonstrated superior air‐ and photo‐stability due to the hydrophobic FPEA₂PbI₄ capping layer that reduces moisture ingress into perovskite structures. Furthermore, a 11.2 cm² large FPEAI‐treated PSC module with a PCE of 13.66% were successfully fabricated. FPEAI passivation is a facile strategy to producing 3D/2D multi‐dimensional PSCs with superior performance and stability.

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Scaling up perovskite solar cells (PSCs) to fabricate efficient perovskite solar modules (PSMs) is the fundamental for application. To make a goal of PSC commercialization achievable, device architecture designs, scalable deposition methods, perovskite morphology modulation, charge transport materials, electrode materials, and encapsulation methods are all important to fabricate stable, low‐cost, and high‐efficiency PSMs.

Abstract

Power conversion efficiency of perovskite solar cells (PSCs) has been boosted to 25.5% among the highest efficiency for single‐junction solar cells, making PSCs extremely promising to realize industrial production and commercialization. Scaling up PSCs to fabricate efficient perovskite solar modules (PSMs) is the fundamental for applications. Here, present progresses on scaling up PSCs are reviewed. The structure design for PSMs is discussed. Various scalable methods and related morphology control strategies for large‐area uniform perovskite films are summarized. Potential charge transport materials and electrode materials together with their scalable methods for low‐cost, efficient, and stable PSMs are also summarized. Besides, current attempts on encapsulation for improving stability and reducing lead leakage are introduced, and the calculated cost and environment influence of PSMs are also outlined.

A C₃N₄ layer functionalized with thiazole is introduced to the electron transfer layer/perovskite interface, which serves as an intermediate energy level to constitute a stepwise energy band alignment and donates the lone pair electrons to undercoordinated Pb²⁺. Resultantly, it effectively passivates the interfacial defects and promotes carrier transport, thereby further boosting the efficiency of the device.

Despite the conspicuous achievements in perovskite solar cells (PSCs), further improvement of the power conversion efficiency (PCE) is hindered by substantially detrimental carrier recombination resulting from the high interfacial charge defect density and inferior charge transport kinetics. Herein, an interface engineering strategy is developed to introduce a Lewis base thiophene or thiazole–modified C₃N₄ layer at the electron transfer layer (ETL)/perovskite interface to constitute a stepwise energy band alignment and passivate defects at interfaces of the perovskite film. Attributed to its well‐matched energy level with TiO₂ and perovskite, the charge extraction efficiency and charge transfer dynamics can be promoted remarkably, greatly inhibiting charge recombination at the interface. Furthermore, thiophene and thiazole can donate the lone pair electrons in S or N atoms to undercoordinated Pb²⁺, which effectively passivates the electronic trap states caused by halogen vacancies, thereby greatly minimizing trap‐assisted nonradiative recombination in the PSCs. Eventually, the thiazole–C₃N₄/perovskite‐based devices acquire an outstanding efficiency of 19.23%, supported by an enhanced open‐circuit voltage (V _OC) of 1.11 V with improved moisture stability. This work provides an avenue for interfacial energy level modulation and defect passivation strategies for a rational interface microstructure design for meliorating the performance of PSCs.

A universal synthetic strategy is proposed for encapsulation and in situ passivation of perovskite nanocrystals in AlPO‐5 zeolite. The perovskite–zeolite composite exhibits enhanced photoluminescence emission and ultrahigh stability under ambient exposure or in water.

Abstract

Metal halide perovskites have been widely applied in optoelectronic fields, but their poor stability hinders their actual applications. A perovskite–zeolite composite was synthesized via in situ growth in air from aluminophosphate AlPO‐5 zeolite crystals and perovskite nanocrystals. The zeolite matrix provides quantum confinement for perovskite nanocrystals, achieving efficient green emission, and it passivates the defects of perovskite by H‐bonding interaction, which leads to a longer lifetime compared to bulk perovskite film. Furthermore, the AlPO‐5 zeolite also acts as a protection shield and enables ultrahigh stability of perovskite nanocrystals under 150 °C heat stress, under a 15‐month long‐term ambient exposure, and even in water for more than 2 weeks, respectively. The strategy of in situ passivation and encapsulation for the perovskite@AlPO‐5 composite was amenable to a range of perovskites, from MA‐ to Cs‐based perovskites. Benefiting from high stability and photoluminescence performance, the composite exhibits great potential to be virtually applied in light‐emitting diodes (LEDs) and backlight displays.

The interface property of perovskite is governed by the surface termination. The combination of ultraviolet photoelectron and metastable‐atom electron spectroscopies is demonstrated as a versatile technique to prove the surface termination. This method is applied to a solution‐processed CH₃NH₃PbI₃ perovskite film to show that the surface is terminated with a layer consisting of CH₃NH₃ and I.

Abstract

The interfaces of a perovskite solar cell significantly influence the charge processes in the cell, which contributes to the device performance with direct implication for surface potential, electronic structure, and chemical reactivity. The properties of the interface are strongly affected by the surface termination. In this work, the combination of ultraviolet photoelectron spectroscopy (UPS) and metastable‐atom electron spectroscopy is demonstrated, to examine the surface termination of a solution‐processed CH₃NH₃PbI₃ perovskite film. The results show that the surface of the CH₃NH₃PbI₃ perovskite film is terminated with a layer consisting of CH₃NH₃ and I. The interface energy level alignment for both occupied and unoccupied levels between CH₃NH₃PbI₃ and C60 is also examined using UPS and low‐energy inverse photoelectron spectroscopy. It turns out that an ideal energy level alignment is established for the electron collection and hole block at the perovskite and C60 interface.