Ligang Yuan

A novel thermionic emission–based interconnecting layer (ICL) for all‐perovskite tandem solar cells is demonstrated with solution‐processed light absorbers, wide absorption, and high efficiency. The novel ICL structure employs a new hybrid system of fluoride silane–incorporated polyethylenimine ethoxylated for solvent resistance and defect passivation.

Abstract

All‐perovskite tandem cells have been considered a potential candidate for bringing the power conversion efficiency (PCE) beyond the Shockley–Queisser limit of single‐junction device while retaining the advantages of earth‐abundant materials and solution processability. However, a challenging issue with regard to realizing such solution‐processed devices is the fulfillment of complex and coupled requirements of the interconnecting layer (ICL), including solvent resistance to protect underlying perovskite film, high electrical properties for carrier transport and recombination, and high optical transmission. In this work, a new thermionic emission–based ICL with enhanced solvent resistance features is demonstrated. Fundamentally, the thermionic emission plays a critical role in the electron transport process in the ICL, which is confirmed through both experimental and theoretical studies. Besides achieving high optical transmission and electrical properties, the new ICL chemically protects the underlying perovskite film by introducing a fluoride silane–incorporated polyethylenimine ethoxylated hybrid system that also passivates the surface defects to reduce electrical loss. The monolithic all‐perovskite tandem cells demonstrate highest PCE of 17.9% (from current density–voltage scan) and the highest steady‐state efficiency is 16.1% for a typical device. Consequently, this work contributes to not only understanding the fundamental mechanism of ICLs but also promotes robust and low‐cost photovoltaics.

2D organolead halide perovskite field effect transistors, which are fabricated based on phase‐pure homologous (n = 1, 2, and 3) Ruddelsden–Popper perovskite (BA)₂(MA) _{n− 1}Pb _n I_{3 n +1} single crystals are demonstrated. A strong dependence of carrier transport behavior of the 2D organolead halide hybrid perovskites on the n value is revealed.

Abstract

This work reveals the intrinsic carrier transport behavior of 2D organolead halide perovskites based on phase‐pure homologous (n = 1, 2, and 3) Ruddelsden–Popper perovskite (RPP) (BA)₂(MA) _{n −1}Pb _n I_3n+1 single crystals. The 2D perovskite field effect transistors with high‐quality exfoliated 2D perovskite bulk crystals are fabricated, and characteristic output and transfer curves are measured from individual single‐crystal flakes with various n values under different temperatures. Unipolar n‐type transport dominated the electrical properties of all these 2D RPP single crystals. The transport behavior of the 2D organolead halide hybrid perovskites exhibits a strong dependence on the n value and the mobility substantially increases as the ratio of the number of inorganic perovskite slabs per organic spacer increases. By extracting the effect of contact resistances, the corrected mobility values for n = 1, 2, and 3 are 2 × 10⁻³, 8.3 × 10⁻², and 1.25 cm² V⁻¹ s⁻¹ at 77 K, respectively. Furthermore, by combining temperature‐dependent electrical transport and optical measurements, it is found that the origin of the carrier mobility dependence on the phase transition for 2D organolead halide perovskites is very different from that of their 3D counterparts. Our findings offer insight into fundamental carrier transport behavior of 2D organic–inorganic hybrid perovskites based on phase‐pure homologous single crystals.

A nearly formamidinium (FA) lead–tin (Pb–Sn) mixed perovskite FAPb_0.75Sn_0.25I₃ is exploited to fabricate a low‐bandgap perovskite solar cell. By combination with a NiO _x hole transport layer, a power conversion efficiency of 17.25% is obtained. This low‐bandgap perovskite solar cell maintains about 91% of its original efficiency at 80 °C for 20 h, which demonstrates good thermal stability.

Abstract

Low bandgap lead–tin (Pb–Sn) mixed perovskite solar cells have achieved high power conversion efficiency in excess of 17%. However, methylammonium (MA) cation is usually contained, and the thermal stability of MA is always a great concern. In this work, according to composition engineering, a nearly formamidinium (FA) based low‐bandgap Pb–Sn mixed perovskite FAPb_0.75Sn_0.25I₃ is being tried to explore as the absorber layer. Combined with interface engineering by replacing poly(3,4‐ethylenedioxythiophene)‐polystyrenesulfonic acid (PEDOT:PSS), layer with NiO _x as hole transport layer, a power conversion efficiency of 17.25% is obtained. This low‐bandgap perovskite solar cell maintains about 91% of its original efficiency at 80 °C for 20 h, and 92% of its initial performance after 46 days storage at the room temperature. The good thermal stability of nearly FA based low‐bandgap perovskite could be good for delivering efficient and stable perovskite‐perovskite tandem solar cells.

Previously unreported nanoscale defects are observed in solution‐processed methylammonium lead tri‐iodide (MAPI) perovskite solar cells. A novel methodology is introduced that eliminates these defects, modifies MAPI crystallinity and enhances power conversion efficiency >30%. In‐situ optoelectronic characterization correlates performance enhancements to improvements in charge collection efficiency, reduced electron–hole recombination, and an overall decrease of trap‐state density.

Abstract

Here, previously unobserved nanoscale defects residing within individual grains of solution‐processed methylammonium lead tri‐iodide (CH₃NH₃PbI₃, MAPI) thin films are identified. Using scanning transmission electron microscopy (STEM), the defects inherently associated with the established solution‐processing methodology are identified, and a facile processing modification to eliminate these defects is introduced. Specifically, defect elimination is achieved by coannealing the as‐deposited MAPI layer with the electron transport layer (phenyl‐C₆₁‐butyric acid methyl, PCBM) resulting in devices that significantly outperform devices prepared using the established methodology—with power conversion efficiencies increasing from 13.6% to 17.4%. The use of transmission electron microscopy allows the correlation of performance enhancements to improved intragrain crystallinity and shows that highly coherent crystallographic orientation results within individual grains when processing is modified. Detailed optoelectronic characterization reveals that the improved intragrain crystallinity drives an improvement of charge collection and a reduction of PEDOT:PSS/perovskite interfacial recombination. The study suggests that the microstructural defects in MAPI, owing to a lack of structural coherence throughout the thickness of thin film, are a significant cause of interfacial recombination.

Perovskite solar cells (PSCs) have undergone rapid development, but the performance degradation accompanied by device upscaling urgently needs a solution. This review covers the research progress on each functional material of large‐area PSCs. A conclusion on the main challenges and an outlook on the research direction of large‐area PSCs are provided.

Abstract

Perovskite solar cells (PSCs) are promising candidates for the next generation of photovoltaic technologies due to their constantly improved efficiencies, which gain much attention from both the scientific and industrial communities. Although the performance of PSCs is dramatically enhanced, most certified or reported high‐efficiency PSCs are still limited to a relatively small active area. The degradation of efficiency and stability accompanied by upscaling must be solved, being a bottleneck toward industrialization. This review focuses on the research progress, challenges, and strategies on large‐area PSCs, especially each functional material in various device architectures, including perovskites, hole transport materials, electron transport materials, and electrodes. Finally, the main issues related to each functional layer of PSCs from laboratory to industry are presented and an outlook on the research direction of large‐area PSCs is given.

Solution‐processed metal oxide nanocrystals present unique properties as efficient carrier transport layers in photovoltaic devices. In this review, solution‐processed metal oxide nanocrystal‐based carrier transport layers in organic solar cells and perovskite solar cells, and their low‐temperature solution‐processed synthesis approaches are summarized.

Abstract

There has been rapid progress in solution‐processed organic solar cells (OSCs) and perovskite solar cells (PVSCs) toward low‐cost and high‐throughput photovoltaic technology. Carrier (electron and hole) transport layers (CTLs) play a critical role in boosting their efficiency and long‐time stability. Solution‐processed metal oxide nanocrystals (SMONCs) as a promising CTL candidate, featuring robust process conditions, low‐cost, tunable optoelectronic properties, and intrinsic stability, offer unique advantages for realizing cost‐effective, high‐performance, large‐area, and mechanically flexible photovoltaic devices. In this review, the recent development of SMONC‐based CTLs in OSCs and PVSCs is summarized. This paper starts with the discussion of synthesis approaches of SMONCs. Then, a broad range of SMONC‐based CTLs, including hole transport layers and electron transport layers, are reviewed, in which an emphasis is placed on the improvement of the efficiency and device stability. Finally, for the better understanding of the challenges and opportunities on SMONC‐based CTLs, several strategies and perspectives are outlined.

Conjugated block copolymers are established as model systems to examine fundamental photophysics in organic donor–acceptor materials. Intramolecular charge transfer within isolated block copolymer chains is quantified. Block copolymer nanoparticles are synthesized to examine the effect of polymer donor aggregation on charge generation. While charge transfer is observed in isolated chains, charge‐separated states are observed only in block copolymer nanoparticles.

Abstract

Fully conjugated donor–acceptor block copolymers are established as model systems to elucidate fundamental mechanisms of photocurrent generation in organic photovoltaics. Using analysis of steady‐state photoluminescence quenching, exciton dissociation to a charge transfer state within individual block copolymer chains is quantified. By making a small adjustment to the conjugated backbone, the electronic properties are altered enough to disrupt charge transfer almost entirely. Strong intermolecular coupling of the electron donor is introduced by synthesizing block copolymer nanoparticles. Transient absorption spectroscopy is used to monitor charge generation in block copolymer isolated chains and nanoparticles. While efficient charge transfer is observed in isolated chains, there is no indication of complete charge separation. In the nanoparticles, long‐lived polarons are observed as early as ≈15 ns. Thus, aggregation of electron donors can facilitate efficient charge generation.

A general nondestructive passivation approach is developed for perovskite solar cells by using 4‐fluoroaniline (FAL). FAL is not only an antisolvent surface modifier, but also a large dipole molecule with a directional field to separate charge at the interface, thus delivering a 20.48% power conversion efficiency with improved stability. Micro/time‐resolved photoluminescence reveals the impact picture of boundary on the local carriers after passivation.

Abstract

Hybrid perovskite thin films are prone to producing surface vacancies during the film formation, which degrade the stability and photovoltaic performance. Passivation via post‐treatment can heal these defects, but present methods are slightly destructive to the bulk of 3D perovskite due to the solvent effect, which hinders fabrication reproducibility. Herein, nondestructive surface/interface passivation using 4‐fluoroaniline (FAL) is established. FAL is not only an effective antisolvent candidate for surface modification, but also a large dipole molecule (2.84 Debye) with directional field for charge separation. Density functional theory calculation reveals that the nondestructive properties are attributed to both the conjugated amine in aromatic ring and the para‐fluoro‐substituent. A hot vapor assisted colloidal process is employed for the post‐treatment. The molecular passivation yields an ultrathin protection layer with a hydrophobic fluoro‐substituent tail and thus enhances the stability and optoelectronic properties. FAL post‐treated perovskite solar cell (PSC) delivers a 20.48% power conversion efficiency under ambient conditions. Micro‐photoluminescence reveals that passivation activates the dark defective state at the surface and interface, delivering the impact picture of boundary on the local carriers. This work demonstrates a generic nondestructive chemical approach for improving the performance and stability of PSCs.

Conventional PbI₂ is replaced by PbI₂/I₂ mixed precursor during the first step of sequential deposition, causing the formation of a PbI₂ porous nanostructure. By changing the content of I₂ in the precursor, the morphology of the PbI₂ film as well as the resulting perovskite film can be successfully modulated. With an optimal content of I₂, a high‐quality perovskite film with a pure phase and smooth surface is achieved, enabling the high performance of perovskite solar cells.

The quality of the perovskite film has a vital influence on the performance of perovskite solar cells and it is quite desirable to simultaneously manipulate the crystallization and morphology of the perovskite film. In this study, conventional PbI₂ is replaced with a PbI₂/I₂ mixed precursor during the first step of sequential deposition, causing the formation of a PbI₂ porous nanostructure. By changing the content of I₂ in the precursor, the morphology of the PbI₂ film as well as the resulting perovskite film can be successfully modulated. With an optimal content of I₂, a high‐quality perovskite film with a pure phase and smooth surface can be achieved. As a result, the conversion efficiency of perovskite solar cells using a PbI₂/I₂ mixed precursor can be as high as 18.63%, compared to 16.89% for the reference device through traditional sequential deposition with a pure PbI₂ precursor.

The impact of Rashba effects in halide perovskites is still under debate. Using femtosecond transient absorption and photoluminescence, it is shown that luminescence from hot carriers is weaker than that of cold carriers, as expected from strongly radiative transitions in direct gap semiconductors. Several possible resolutions to this, including lattice dynamics that overcome Rashba splittings at room temperature are considered.

Abstract

The generation and recombination of charge carriers in semiconductors through photons controls photovoltaic and light‐emitting diode operation. Understanding of these processes in hybrid perovskites has advanced, but remains incomplete. Using femtosecond transient absorption and photoluminescence, it is observed that the luminescence signal shows a rise over 2 ps, while initially hot photogenerated carriers cool to the band edge. This indicates that the luminescence from hot carriers is weaker than that of cold carriers, as expected from strongly radiative transitions in direct gap semiconductors. It is concluded that the electrons and holes show a strong overlap in momentum space, despite recent proposals that Rashba splitting leads to a band offset suppressing such an overlap. A number of possible resolutions to this, including lattice dynamics that remove the Rashba splitting at room temperature, and localization of luminescence events to length scales below 10 nm are considered.

A graded bilayered inorganic hole‐transporting layer (including compact NiO _x and mesoporous CuGaO₂) is developed for inverted perovskite solar cells. The resulting devices demonstrate both high efficiency, with the champion one giving a stabilized efficiency of ≈20% and superior thermal stability with >80% of the initial efficiency being retained subject to 1000 hours' thermal aging at 85 °C.

Abstract

The unstable feature of the widely employed organic hole‐transporting materials (HTMs) (e.g., spiro‐MeOTAD) significantly limits the practical application of perovskite solar cells (PSCs). Therefore, it is desirable to design new structured PSCs with stable HTMs presenting excellent carrier extraction and transfer properties. This work demonstrates a new inverted PSC configuration. The new PSC has a graded band alignment and bilayered inorganic HTMs (i.e., compact NiO_x and mesoporous CuGaO₂). In comparison with planar‐structured PSCs, the mesoporous CuGaO₂ can effectively extract holes from perovskite due to the increased contact area of the perovskite/HTM. The graded energy alignment constructed in the ultrathin compact NiO_x, mesoporous CuGaO₂, and perovskite can facilitate carrier transfer and depress charge recombination. As a result, the champion device based on the newly designed mesoscopic PSCs yields a stabilized efficiency of ≈20%, which is considered one of the best results for inverted PSCs with inorganic HTMs. Additionally, the unencapsulated PSC device retains more than 80% of its original efficiency when subjected to thermal aging at 85 °C for 1000 h in a nitrogen atmosphere, thus demonstrating superior thermal stability of the device. This study may pave a new avenue to rational design of highly efficient and stable PSCs.

A novel SnO₂‐in‐polymer matrix is demonstrated to be an excellent electron‐selective layer in perovskite solar cells. The polymer is uniformly dispersed in SnO₂ colloidal ink and promotes the nanoparticle disaggregation in the ink. Planar‐structure perovskite solar cells based on this SnO₂‐in‐polymer matrix show a high efficiency of 20.8% with negligible hysteresis and superior reproducibility.

Abstract

Understanding interfacial loss and the ways to improving interfacial property is critical to fabricate highly efficient and reproducible perovskite solar cells (PSCs). In SnO₂‐based PSCs, nonradiative recombination sites at the SnO₂–perovskite interface lead to a large potential loss and performance variation in the resulting photovoltaic devices. Here, a novel SnO₂‐in‐polymer matrix (i.e., polyethylene glycol) is devised as the electron transporting layer to improve the film quality of the SnO₂ electron transporting layer. The SnO₂‐in‐polymer matrix is fabricated through spin‐coating a polymer‐incorporated SnO₂ colloidal ink. The polymer is uniformly dispersed in SnO₂ colloidal ink and promotes the nanoparticle disaggregation in the ink. Owing to polymer incorporation, the compactness and wetting property of SnO₂ layer is significantly ameliorated. Finally, photovoltaic devices based on Cs_0.05FA_0.81MA_0.14PbI_2.55Br_0.45 perovskite sandwiched between SnO₂ and Spiro‐OMeTAD layer are fabricated. Compared with the averaging power conversion efficiency of 16.2% with 1.2% deviation for control devices, the optimized devices exhibit an improved averaging efficiency of 19.5% with 0.25% deviation. The conception of polymer incorporation in the electron transporting layer paves a way to further increase the performance of planar perovskite solar cells.

High‐efficiency (21.06%) and durable 2D–3D vertical aligned perovskite solar cells (PSCs) with phase pure 2D perovskite are demonstrated. The phase pure 2D perovskite minimizes photo‐generated charge‐carrier localization in the low‐dimensional perovskite; the dominant vertical alignment does not affect charge‐carrier extraction. The traditional constraint of trade‐off between efficiency and stability in PSC is overcome.

Abstract

Three‐dimensional (3D) metal‐halide perovskite solar cells (PSCs) have demonstrated exceptional high efficiency. However, instability of the 3D perovskite is the main challenge for industrialization. Incorporation of some long organic cations into perovskite crystal to terminate the lattice, and function as moisture and oxygen passivation layer and ion migration blocking layer, is proven to be an effective method to enhance the perovskite stability. Unfortunately, this method typically sacrifices charge‐carrier extraction efficiency of the perovskites. Even in 2D–3D vertically aligned heterostructures, a spread of bandgaps in the 2D due to varying degrees of quantum confinement also results in charge‐carrier localization and carrier mobility reduction. A trade‐off between the power conversion efficiency and stability is made. Here, by introducing 2D C₆H₁₈N₂O₂PbI₄ (EDBEPbI₄) microcrystals into the precursor solution, the grain boundaries of the deposited 3D perovskite film are vertically passivated with phase pure 2D perovskite. The phases pure (inorganic layer number n = 1) 2D perovskite can minimize photogenerated charge‐carrier localization in the low‐dimensional perovskite. The dominant vertical alignment does not affect charge‐carrier extraction. Therefore, high‐efficiency (21.06%) and ultrastable (retain 90% of the initial efficiency after 3000 h in air) planar PSCs are demonstrated with these 2D–3D mixtures.

Near‐infrared nonfullerene acceptors (NIR NFAs, T1–T4) with fluorinated regioisomeric A–Aπ–D–Aπ–A backbones are developed for high‐performance polymer solar cells (PSCs), in which proximal NFAs with varied F‐atoms (T1–T3) largely outperform distal NFA (T4). Particularly, single‐junction PSCs with a PTB7‐Th:T2 blend can achieve 10.87% power conversion efficiency (PCE), and tandem PSCs through integrating with an ITIC:PBDB‐T blend reach a PCE of 14.64%.

Abstract

Solar photon‐to‐electron conversion with polymer solar cells (PSCs) has experienced rapid development in the recent few years. Even so, the exploration of molecules and devices in efficiently converting near‐infrared (NIR) photons into electrons remains critical, yet challenging. Herein presented is a family of near‐infrared nonfullerene acceptors (NIR NFAs, T1–T4) with fluorinated regioisomeric A–Aπ–D–Aπ–A backbones for constructing efficient single‐junction and tandem PSCs with photon response up to 1000 nm. It is found that the tuning of the regioisomeric bridge (Aπ) and fluoro (F)‐substituents on a molecular skeleton strongly influences the backbone conformation and conjugation, leading to the optimized optoelectronic and stable stacking of resultant NFAs, which eventually impacts the performance of derived PSCs. In PSCs, the proximal NFAs with varied F‐atoms (T1–T3) mostly outperform than that of distal NFA (T4). Notably, single‐junction PSC with PTB7‐Th:T2 blend can reach 10.87% power conversion efficiency (PCE), after implementing a solvent additive to improve blend morphology. Moreover, efficient tandem PSCs are fabricated through integrating such NIR cells with mediate bandgap nonfullerene‐based subcells, to achieve a PCE of 14.64%. The results reveal the structural design of organic semiconductor and device with improved photovoltaic performance.

Hybrid cation (guanidinium/formamidinium) tin‐based perovskites that give a new performance record for lead‐free perovskite solar cells (power conversion efficiency = 9.6%) are demonstrated. The fabricated devices show an incredible light‐soaking stability for continuous 1 sun illumination for 1 h, and the device passes all harsh verification steps to attain a certified efficiency of 8.3% for a fresh cell.

Abstract

The stability of a tin‐based perovskite solar cell is a major challenge. Here, hybrid tin‐based perovskite solar cells in a new series that incorporate a nonpolar organic cation, guanidinium (GA⁺), in varied proportions into the formamidinium (FA⁺) tin triiodide perovskite (FASnI₃) crystal structure in the presence of 1% ethylenediammonium diiodide (EDAI₂) as an additive, are reported. The device performance is optimized at a precursor ratio (GAI:FAI) of 20:80 to attain a power conversion efficiency (PCE) of 8.5% when prepared freshly; the efficiencies continuously increase to attain a record PCE of 9.6% after storage in a glove‐box environment for 2000 h. The hybrid perovskite works stably under continuous 1 sun illumination for 1 h and storage in air for 6 days without encapsulation. Such a tin‐based perovskite passes all harsh standard tests, and the efficiency of a fresh device, 8.3%, is certified. The great performance and stability of the device reported herein attains a new milestone for lead‐free perovskite solar cells on a path toward commercial development.

An important design principle for perovskite light‐emitting diodes is discovered regarding optimal perovskite thickness. Adopting a thinner perovskite layer is beneficial for both device efficiency and stability, with external quantum efficiency (EQE) as high as 17.6% being achieved. The improved EQE is primarily due to better light outcoupling, and the improved stability is correlated with reduced Joule heating.

Abstract

Hybrid organic–inorganic perovskite semiconductors have shown potential to develop into a new generation of light‐emitting diode (LED) technology. Herein, an important design principle for perovskite LEDs is elucidated regarding optimal perovskite thickness. Adopting a thin perovskite layer in the range of 35–40 nm is shown to be critical for both device efficiency and stability improvements. Maximum external quantum efficiencies (EQEs) of 17.6% for Cs_0.2FA_0.8PbI_2.8Br_0.2, 14.3% for CH₃NH₃PbI₃ (MAPbI₃), 10.1% for formamidinium lead iodide (FAPbI₃), and 11.3% for formamidinium lead bromide (FAPbBr₃)‐based LEDs are demonstrated with optimized perovskite layer thickness. Optical simulations show that the improved EQEs source from improved light outcoupling. Furthermore, elevated device temperature caused by Joule heating is shown as an important factor contributing to device degradation, and that thin perovskite emitting layers maintain lower junction temperature during operation and thus demonstrate increased stability.

The sensitive detection of X‐rays embodies an important research area, being motivated by a common desire to minimize the radiation doses required for detection. In article number 1804550, Julian A. Steele, Maarten B. J. Roeffaers, and co‐workers detail the photophysical properties contributing to the impressive performance of highly sensitive X‐ray detectors based on double perovskite Cs₂AgBiBr₆. Upon cooling the device, enormous performance enhancements are realized and are tracked via optical‐based studies, closing the gap between the interpretation of high‐ and low‐energy photogenerated charges.

In article number 1804372, Jr‐Hau He and co‐workers study the influences of the surface effect of 2D layered perovskites before and after mechanical exfoliation. The smooth 2D perovskite is less sensitive to ambient moisture and exhibits a considerably low dark current. This work reveals the strong dependence of the surface condition of 2D hybrid perovskite crystals on their moisture stability and optoelectronic properties.

The utilization of poly(vinylpyrrolidone) (PVP) as a cathode interlayer is demonstrated in inverted and conventional devices via both the self‐organization method and the step‐by‐step preparation method. The driving forces for PVP migration are the high surface energy of the PVP and the strong intermolecular interaction between the PVP and the bottom cathode. In addition, the PVP‐modified devices have excellent stability in air and show insensitivity to PVP molecular weight.

Abstract

Herein, poly(vinylpyrrolidone) (PVP) is used as the cathode interlayer (CIL) through the self‐organization method in inverted organic solar cells (OSCs). By coating a solution of PVP and active layer materials onto a glass/indium tin oxide (ITO) substrate, the PVP can segregate to the near ITO side due to its high surface energy and strong intermolecular interaction with the ITO electrode. The power conversion efficiency (PCE) of the obtained OSC device reaches 13.3%, much higher than that of the control device with a PCE of only 10.1%. The improvement results from the increased exciton dissociation efficiency and the depressed trap‐assisted recombination, which can be attributed to the reduced work function of the cathode by the self‐organized PVP. Additionally, the molecular weight of the PVP has almost no influence on the device performance, and the PVP‐modified device presents superior stability. This method can also be applied in other highly efficient fullerene‐free OSCs, and with a fine selection of the active layer, a high PCE of 14.0% is obtained. Overall, this work demonstrates the great potential of the PVP‐based CIL in inverted OSCs fabricated via the self‐organization method.

Based on the high humidity stable [(NH₄)_2.4(FA)₈Pb₉I_28.4]_0.85(MAPbBr₃)_0.15 mixed‐dimensional perovskite, the authors investigated its aging properties under different humidity levels. Through analyzing the performance changes during aging, the authors speculated, and verified the possible mechanism of its high moisture resistance, which is a result from the formation of NH₄PbX₃*(H₂O)₂ and two‐dimensional protective layers, and the conversion of δ‐phase FAPbI₃ into α‐phase under continuous illumination.

Recently, perovskite materials are widely applied in the photovoltaic field, whereas its practical application is hindered by the humidity instability. To solve this problem, the authors prepared a [(NH₄)_2.4(FA)₈Pb₉I_28.4]_0.85(MAPbBr₃)_0.15 mixed‐dimensional (MD) perovskite with superior humidity stability. Herein, we investigated the aging properties of three‐dimensional (3D) and MD perovskite under different humidity levels. Through analyzing the performance changes before and after aging tests, the possible mechanism of high moisture resistance for MD perovskite is speculated and verified. After undergoing cation exchange, the surface NH₄ ⁺ combines with H₂O to form NH₄PbX₃*(H₂O)₂ (X = I or Br), and then the two‐dimensional (2D) perovskite protective layers are formed on the surface of perovskite, which prevent H₂O from destroying the 3D perovskite structure. Meanwhile, under continuous illumination, the δ‐phase FAPbI₃ produced from inside FA⁺ may change into α‐phase FAPbI₃. Therefore, the MD perovskite maintains great 3D perovskite structure and displays outstanding humidity stability under high humidity. The devices retain their starting photoelectric conversion efficiency (PCE) for 4000 h under 40% relative humidity (RH) and 80% of PCE over 2000 h under 70% RH. This finding provides a promising prospect for solving the humidity instability of perovskite materials and will promote the development of PSCs.

Conventional PbI₂ is replaced by PbI₂/I₂ mixed precursor during the first step of sequential deposition, causing the formation of a PbI₂ porous nanostructure. By changing the content of I₂ in the precursor, the morphology of the PbI₂ film as well as the resulting perovskite film can be successfully modulated. With an optimal content of I₂, a high‐quality perovskite film with a pure phase and smooth surface is achieved, enabling the high performance of perovskite solar cells.

The quality of the perovskite film has a vital influence on the performance of perovskite solar cells and it is quite desirable to simultaneously manipulate the crystallization and morphology of the perovskite film. In this study, conventional PbI₂ is replaced with a PbI₂/I₂ mixed precursor during the first step of sequential deposition, causing the formation of a PbI₂ porous nanostructure. By changing the content of I₂ in the precursor, the morphology of the PbI₂ film as well as the resulting perovskite film can be successfully modulated. With an optimal content of I₂, a high‐quality perovskite film with a pure phase and smooth surface can be achieved. As a result, the conversion efficiency of perovskite solar cells using a PbI₂/I₂ mixed precursor can be as high as 18.63%, compared to 16.89% for the reference device through traditional sequential deposition with a pure PbI₂ precursor.

Non‐peripheral octamethyl‐substituted copper (II) phthalocyanine nanowires are incorporated in poly(3‐hexylthiophene) to form nanocomposite, which exhibited higher hole mobilities and well‐matched energy levels. A power conversion efficiency of 16.61% is achieved for a perovskite solar cell based on composite hole‐transport material which retains 90% of their initial efficiencies after 800 h of storage at 25 °C with a relative humidity of 75% without any encapsulations.

New efficient hole‐transport material (HTM) composites based on low‐cost easy‐preparation non‐peripheral octamethyl‐substituted copper (II) phthalocyanine (N‐CuMe₂Pc) nanowire and poly(3‐hexylthiophene) (P3HT) are developed for CH₃NH₃PbI₃ (MAPbI₃)‐based perovskite solar cells (PSCs). Compared with pristine P3HT, the prepared nanocomposite HTMs provided thin films with better qualities and reduced trap densities, and exhibited higher hole mobilities and well‐matched energy levels with the perovskite layer. Depending on the ratio of the two components, the power conversion efficiency (PCE) reached up to 16.61%, which is higher than the efficiency of the standard device based on doped spiro‐OMeTAD (16.13%). Moreover, the long‐term stability of the PSCs is also improving greatly. The best performing devices based on P1C1 HTM retained 90% of their initial efficiencies after 800 h of storage with a relative humidity of 75%. These results indicate N‐CuMe₂Pc nanowire/P3HT nanocomposites can be an effective HTM to realize superior performance in PSCs.

The theoretical power conversion efficiency of all‐inorganic CsPbI₂Br perovskite solar cells is predicted to be 22.1%, and only by taking both material chemistry and device physics into consideration can researchers achieve this goal.

Cesium‐based all‐inorganic perovskite solar cells (PSCs), especially for CsPbI₂Br component‐based devices, have attracted increasing attention due to its advantage of superior thermal and phase stability. Since the pioneering study reported in 2016, more than 30 papers have been published, reporting the rapid boost in the power conversion efficiency (PCE) of PSCs to 14.81%. The CsPbI₂Br PSC is one of the most remarkable research hotspots in the field of perovskite photovoltaics. In this progress report, the recent advances in CsPbI₂Br PSCs are systematically reviewed, which in turn introduces the basic property and stability of active layers, and the performance improvements in these devices. The challenges as well as the possible solutions toward better‐performing CsPbI₂Br PSCs are also discussed. The theoretical calculation results point out that there is much room for further device performance enhancement, particularly in open‐circuit voltages. This progress report focuses on CsPbI₂Br material properties and summarizes recent strategies to improve the corresponding device's PCE, in order to open new perspectives toward commercial utility of PSCs.