Efficient Inverted Perovskite Solar Cells with a Fill Factor Over 86% via Surface Modification of the Nickel Oxide Hole Contact

The poor interface quality between nickel oxide (NiO_x) and halide perovskites limits the performance and stability of NiO_x-based perovskite solar cells (PSCs). Here a reactive surface modification approach based on the in situ decomposition of urea on the NiO_x surface is reported. The pyrolysis of urea can reduce the high-valence state of nickel and replace the adsorbed hydroxyl group with isocyanate. Combining theoretical and experimental analyses, the treated NiO_x films present suppressed surface states and improved transport energy level alignment with the halide perovskite absorber. With this strategy, NiO_x-based PSCs achieve a champion power conversion efficiency (PCE) of 23.61% and a fill factor of over 86%. The device's efficiency remains above 90% after 2000 h of thermal aging at 85 °C. Furthermore, perovskite solar modules achieve PCE values of 18.97% and 17.18% for areas of 16 and 196 cm², respectively.     

3D Polydentate Complexing Agents for Passivating Defects and Modulating Crystallinity for High-Performance Perovskite Solar Cells

The grain boundaries (GBs)/surface defects within perovskite film directly impede the further improvement of photoelectric conversion efficiency (PCE) and stability of planar perovskite solar cells (PSCs). Herein, 3D phytic acid (PA) and phytic acid dipotassium (PAD) with polydentate are explored to synchronously passivate the defects of perovskite absorber directly in multiple spatial directions. The strong electron-donating groups ( H₂PO₄) in the PA molecule afford six anchor sites to bind firmly with uncoordinated Pb²⁺ at the GBs/surface and modulate perovskite crystallization, thus enhancing the quality of perovskite film. Particularly, PAD containing an additional (K→PO) push–pull structure promotes the dominant coordination of phosphate group (PO) with Pb²⁺ and passivates halide anion defects due to the complexation of potassium ions (K⁺) with iodide ions (I^-). Consequently, the PAD-complexed PSCs deliver a champion PCE of 23.18%, which is remarkably higher than that of the control device (19.94%). Meanwhile, PAD-complexed PSCs exhibit superior moisture and thermal stability, remaining 79% of their initial PCE after 1000 h under continuous illumination, while the control device remain only 48% of their PCE after 1000 h. This work provides important insights into designing multifunctional 3D passivators for the purpose of simultaneously enhancing the efficiency and stability of devices.     

Low-Dimensional 2-thiopheneethylammonium Lead Halide Capping Layer Enables Efficient Single-Junction Methylamine-Free Wide-Bandgap and Tandem Perovskite Solar Cells

Wide-bandgap (WBG) perovskite solar cells (PSCs) have garnered significant attention for their potential applications in tandem solar cells. However, their large open-circuit voltage (V_OC) deficit and serious photo-induced halide segregation remain the main challenges that impede their applications. Herein, a post-treatment strategy without thermal annealing is presented to form a 2D top layer of 2-thiopheneethylammonium lead halide (n = 1) on WBG perovskites. This thermal annealing-free post-treatment method can more effectively passivate the defects of WBG methylamine (MA)-free formamidinium/cesium lead iodide/bromide perovskite films and suppress photo-induced perovskite phase segregation, as compared with the thermal annealing method that yields multi-2D phases. The resulting opaque and semi-transparent 1.66 eV-bandgap perovskite solar cells deliver maximum power conversion efficiencies of 21.47% (a small V_OC deficit of 0.43 V) and 19.11%, respectively, both of which are among the highest reports for inverted MA-free WBG PSCs. Consequently, four-terminal all-perovskite tandem cells realize a remarkable efficiency of 26.64%, showing great promise for their applications in efficient multi-junction tandem solar cells.     

Enhanced Performance of Planar Perovskite Solar Cells Induced by Van Der Waals Epitaxial Growth of Mixed Perovskite Films on WS2 Flakes

Organic–inorganic metal halide perovskite solar cells (PSCs) have attracted much research interest owing to their high power conversion efficiency (PCE), solution processability, and the great potential for commercialization. However, the device performance is closely related to the quality of the perovskite film and the interface properties, which cannot be easily controlled by solution processes. Here, 2D WS₂ flakes with defect‐free surfaces are introduced as a template for van der Waals epitaxial growth of mixed perovskite films by solution process for the first time. The mixed perovskite films demonstrate a preferable growth along (001) direction on WS₂ surfaces. In addition, the WS₂/perovskite heterojunction forms a cascade energy alignment for efficient charge extraction and reduced interfacial recombination. The inverted PSCs with WS₂ interlayers show high PCEs up to 21.1%, which is among the highest efficiency of inverted planar PSCs. This work demonstrates that high‐mobility 2D materials can find important applications in PSCs as well as other perovskite‐based optoelectronic devices.     

24.64%-Efficiency MA-Free Perovskite Solar Cell with Voc of 1.19 V Enabled by a Hinge-Type Fluorine-Rich Complex

High density of defects at interface severely affects the performance of perovskite solar cells (PSCs). Herein, cobalt (II) hexafluoro-2,4-pentanedionat (CoFAc), a hinge-type fluorine-rich complex, is introduced onto the surface of formamidinium cesium lead iodide (FACsPbI₃) film to address the issues of perovskite/Spiro-OMeTAD interface. The existence of CoFAc passivates both organic cation and halide anion vacancies by establishing powerful hydrogen bonds with HC(NH₂)₂⁺ (FA⁺) and strong ionic bonds with Pb²⁺ in perovskite films. In addition, CoFAc serves as a connecting link to enhance interfacial hole-transport kinetics via interacting with Spiro-OMeTAD. Consequently, FACsPbI₃ PSCs with CoFAc modification display a champion power conversion efficiency (PCE) of 24.64% with a charming open-circuit voltage (V_OC) of 1.191 V, which is the record V_OC among all the reported organic-inorganic hybrid PSCs with TiO₂ as electron transport layer. Furthermore, CoFAc-modified devices exhibit an outstanding long-term stability, which can maintain 95% of their initial PCEs after exposure to ambient atmosphere for 1500 h without any encapsulation.     

Efficient and Stable Quasi-2D Perovskite Solar Cells Enabled by Thermal-Aged Precursor Solution

Quasi-2D perovskites have received wide attention in photovoltaics owing to their excellent materials robustness and merits in the device stability. However, the highest power conversion efficiency (PCE) reported on quasi-2D perovskite solar cells (PSCs) still lags those of the 3D counterparts, mainly caused by the relatively high voltage loss. Here, a study is presented on the mitigation of voltage loss in quasi-2D PSCs via usage of thermal-aged precursor solutions (TAPSs). Based on the (AA)₂MA₄Pb₅I₁₆ (n = 5) quasi-2D perovskite absorber with a bandgap of ≈1.60 eV, a record-high open-circuit voltage of 1.24 V is obtained, resulting in boosting the PCE to 18.68%. The enhanced photovoltaic performance afforded by TAPS is attributed to the thermal-aged solution processing that triggers colloidal aggregations to reduce the nucleation sites inside the solution. As a result, formation of high-quality perovskite films featuring compact morphology, preferential crystal orientation, and lowered trap density is allowed. Of importance, with the improved film quality, the corrosion of Ag electrode induced by ion migrations is effectively restrained, which leads to a satisfactory storage stability with <2% degradation after 1200 h under nitrogen environment without encapsulation.     

Introduction of Hydrophobic Ammonium Salts with Halogen Functional Groups for High‐Efficiency and Stable 2D/3D Perovskite Solar Cells

2D perovskites have attracted extensive attention due to their excellent stability compared with 3D perovskites. However, the intrinsic hydrophilicity of introduced alkylammonium salts effects the humidity stability of 2D/3D perovskites. Devices based on longer chain alkylammonium salts show improvement in hydrophobicity but lower efficiency due to the poorer charge transport among various layers. To solve this issue, two hydrophobic short‐chain alkylammonium salts with halogen functional groups (2‐chloroethylamine, CEA⁺ and 2‐bromoethylamine, BEA⁺) are introduced into (Cs_0.1FA_0.9)Pb(I_0.9Br_0.1)₃ 3D perovskites to form 2D/3D perovskite structure, which achieve high‐quality perovskite films with better crystallization and morphology. The optimal 2D/3D perovskite solar cells (PSCs) with 5% CEA⁺ display a power conversion efficiency (PCE) as high as 20.08% under 1 sun irradiation. Because of the notable hydrophobicity of alkylammonium cations with halogen functional groups and the formed 2D/3D perovskite structure, the optimal PSCs exhibit superior moisture resistance and retain 92% initial PCE after aging at 50 ± 5% relative humidity for 2400 h. This work opens up a new direction for the design of new‐type 2D/3D PSCs with improved performance by employing proper alkylammonium salts with different functional groups.     

Managing Interfacial Hot-Carrier Cooling and Extraction Kinetics for Inverted Ma-Free Perovskite Solar Cells Over 23% Efficiency via Dion–Jacobson 2D Capping Layer

While quasi-2D perovskite is often used in inverted perovskite solar cells (PSCs) to improve the interfacial carrier transfer, the development of pure 2D perovskite with superior stability is rarely seen and the corresponding carrier-extraction kinetics remains unclear. Here, a variety of hexatomic ring cations including piperidine, pyridine, and cyclohexane are introduced to modify the perovskite/electron transport layer interface. The Dion–Jacobson phase 2D cladding (n = 1) based on 3-(aminomethyl) piperidinium is proved to form a coordinated energy landscape and homogeneous surface potential distribution, and effectively prolong the electron diffusion length (≈1.58 µm) and accelerate the hot-carrier extraction rate (2.5 times that of Control at 400 K). Furthermore, the quasi-2D treatment (n ≈ 3,4) demonstrated a slight escalation in short-circuit current, but failed to inhibit the interdiffusion of Ag, Pb, and I under illumination. Finally, one of the state-of-art power conversion efficiency (PCE) for MA-free inverted PSCs is achieved at 23.62% with increased open-circuit voltage (≈1.15 V) and fill factor (≈82.8%). Most importantly, 89% and 93.6% of initial PCE are retained after 720 h under 85 °C heating and 1000 h under maximum power point tracking, illustrating satisfactory thermal and operational stability with pure 2D perovskite capping layer.     

Suppressing the Photoinduced Halide Segregation in Wide-Bandgap Perovskite Solar Cells by Strain Relaxation

Efficient and stable wide bandgap (WBG) perovskite solar cells (PSCs) are imperative for fabricating superior tandem devices. However, small crystal grains and light-induced phase segregation of WBG perovskite result in large open-circuit voltage (V_OC) deficits, critically impeding the development of the related devices. Herein, the effective functional groups of Lewis-base trans-Ferulic acid (t-FA) are employed to release the residual microstrain in the perovskite lattice. Larger perovskite crystals are formed by strengthening the interaction between the perovskite solute and solution. The lattice structure is stabilized to suppress light-induced halide segregation. Finally, the power conversion efficiency (PCE) of the optimized device with a bandgap of ≈1.77 eV is increased from 17.33% to 19.31% with the enhancement of V_OC. Moreover, replacing a mixture of MeO-2PACZ and Me-4PACZ as the hole transporting layer (HTL), the PCE further lifts to 19.9% and V_OC is 1.32 V, one of the highest performances reported for WBG PSCs, especially for devices prepared entirely by solution spin-coating. Therefore, this study provides a practicable alternative for realizing efficient WBG PSCs, which can contribute to the growth of perovskite-based tandem devices.     

Illumination Enhanced Crystallization and Defect Passivation for High Performance CsPbI3 Perovskite Solar Cells by Sacrificing Dye

All-inorganic perovskite solar cells (PSCs) have been the research focus due to their high thermal stability and proper band gap for tandem solar cells. However, their power conversion efficiency (PCE) is still lower than that of organic-inorganic hybrid PSCs. Herein, a sacrificing dye (Rhodamine B isothiocyanate, RBITC) is developed to regulate the growth of perovskite film by in situ release of ethylammonium cations, isothiocyanate anions and benzoic acid molecules upon annealing and illumination. The ethylammonium cations can efficiently passivate surface defects. The isothiocyanate anions incorporate with uncoordinated Pb to regulate the crystallization process. The benzoic acid molecules facilitate the nucleation of the perovskite crystals. Especially, the illumination can accelerate the release of these beneficial ions/molecules to improve the quality of perovskite films further. After optimization with RBITC, a high open circuit voltage (V_OC) of 1.24 V and a champion PCE of 20.95% are obtained, which are among the highest Voc and PCE values of CsPbI₃ PSCs. Accordingly, the operational stability of the PSC devices is significantly improved. The results provide an efficient chemical strategy to regulate the formation of perovskite films in whole crystallization process for high performance all-inorganic PSCs.     

Boosting Photovoltaic Performance for Lead Halide Perovskites Solar Cells with BF4− Anion Substitutions

Composition engineering is a particularly simple and effective approach especially using mixed cations and halide anions to optimize the morphology, crystallinity, and light absorption of perovskite films. However, there are very few reports on the use of anion substitutions to develop uniform and highly crystalline perovskite films with large grain size and reduced defects. Here, the first report of employing tetrafluoroborate (BF₄^?) anion substitutions to improve the properties of (FA = formamidinium, MA = methylammonium (FAPbI₃)_0.83(MAPbBr₃)_0.17) perovskite films is demonstrated. The BF₄^? can be successfully incorporated into a mixed‐ion perovskite crystal frame, leading to lattice relaxation and a longer photoluminescence lifetime, higher recombination resistance, and 1–2 orders magnitude lower trap density in prepared perovskite films and derived solar cells. These advantages benefit the performance of perovskite solar cells (PVSCs), resulting in an improved power conversion efficiency (PCE) of 20.16% from 17.55% due to enhanced open‐circuit voltage (V_OC) and fill factor. This is the highest PCE for BF₄^? anion substituted lead halide PVSCs reported to date. This work provides insight for further exploration of anion substitutions in perovskites to enhance the performance of PVSCs and other optoelectronic devices.     

An Ultrathin Ferroelectric Perovskite Oxide Layer for High‐Performance Hole Transport Material Free Carbon Based Halide Perovskite Solar Cells

The hole transport material (HTM) free carbon based perovskite solar cells (C‐PSCs) are promising for its manufactural simplicity, but they currently suffer from low power conversion efficiencies (PCE) largely because of the voltage loss. Here, a new strategy to increase the PCE by incorporating an ultrathin ferroelectric oxide PbTiO₃ layer between the electron transport material and the halide perovskite is reported. The resulting C‐PSCs have achieved PCEs up to 16.37%, which is the highest record for HTM‐free C‐PSCs to date, mainly ascribable to the ferroelectric layer enhanced open circuit voltage. Detail measurements and analysis show an enhanced built‐in potential in the C‐PSCs as well as suppression of the non‐radiative recombination due to the ferroelectric PbTiO₃ layer incorporation, accounting for the boosted V_OC and photovoltaic performance.     

Efficient and Ambient‐Air‐Stable Solar Cell with Highly Oriented 2D@3D Perovskites

3D organic–inorganic lead halide perovskites have shown great potential in efficient photovoltaic devices. However, the low stability of the 3D perovskite layer and random arrangement of the perovskite crystals hinder its commercialization road. Herein, a highly oriented 2D@3D ((AVA)₂PbI₄@MAPbI₃) perovskite structure combining the advantages of both 2D and 3D perovskite is fabricated through an in situ route. The highest power conversion efficiency (PCE) of 18.0% is observed from a 2D@3D perovskite solar cell (PSC), and it also shows significantly enhanced device stability under both inert (90% of initial PCE for 32 d) and ambient conditions (72% of initial PCE for 20 d) without encapsulation. The high efficiency of 18.0% and nearly twofold improvement of device stability in ambient compared with pure 3D PSCs confirm that such 2D@3D perovskite structure is an effective strategy for high performance and increasing stability and thus will enable the timely commercialization of PSCs.     

High Efficiency and High Open Circuit Voltage in Quasi 2D Perovskite Based Solar Cells

An important property of hybrid layered perovskite is the possibility to reduce its dimensionality to provide wider band gap and better stability. In this work, 2D perovskite of the structure (PEA)₂(MA)_n–1Pb_nBr_3n+1 has been sensitized, where PEA is phenyl ethyl‐ammonium, MA is methyl‐ammonium, and using only bromide as the halide. The number of the perovskite layers has been varied (n) from n = 1 through n = ∞. Optical and physical characterization verify the layered structure and the increase in the band gap. The photovoltaic performance shows higher open circuit voltage (V_oc) for the quasi 2D perovskite (i.e., n = 40, 50, 60) compared to the 3D perovskite. V_oc of 1.3 V without hole transport material (HTM) and V_oc of 1.46 V using HTM have been demonstrated, with corresponding efficiency of 6.3% and 8.5%, among the highest reported. The lower mobility and transport in the quasi 2D perovskites have been proved effective to gain high V_oc with high efficiency, further supported by ab initio calculations and charge extraction measurements. Bromide is the only halide used in these quasi 2D perovskites, as mixing halides have recently revealed instability of the perovskite structure. These quasi 2D materials are promising candidates for use in optoelectronic applications that simultaneously require high voltage and high efficiency.     

Spidermen Strategy for Stable 24% Efficiency Perovskite Solar Cells

The interface energetics-modification plays an important role in improving the power conversion efficiency (PCE) among the perovskite solar cells (PSCs). Considering the low carrier mobility caused by defects in PSCs, a double-layer modification engineering strategy is adopted to introduce the “spiderman” NOBF₄ (nitrosonium tetrafluoroborate) between tin dioxide (SnO₂ and perovskite layers. NO⁺, as the interfacial bonding layer, can passivate the oxygen vacancy in SnO₂, while BF₄⁻ can optimize the defects in the bulk of perovskite. This conclusion is confirmed by theoretical calculation and transmission electron microscopy (TEM). The synergistic effect of NO⁺ and BF₄⁻ distinctly heightens the carrier extraction efficiency, and the PCE of PSCs is 24.04% with a fill factor (FF) of 82.98% and long-term stability. This study underlines the effectiveness of multifunctional additives in improving interface contact and enhancing PCE of PSCs.     

Molten Salt Strategy for Reproducible Evaporation of Efficient Perovskite Solar Cells

Vacuum evaporation is promising for the scalable fabrication of perovskite solar cells (PSCs). Nevertheless, the poor thermal conductivity of metal halide powder leads to unfavorable temperature inhomogeneity, which destabilizes the evaporation rate, posing a major challenge to the reproducible deposition of perovskite films, particularly by coevaporation. Herein, a molten salt strategy is reported for sequentially vacuum evaporation of PSCs. The molten salt increases the thermal conductivity of metal halides and greatly homogenizes the temperature, which stabilizes the evaporation rate and the composition of the resulting perovskite films. The PSCs yield power conversion efficiencies (PCEs) of ≈24% with exceptional reproducibility. The unencapsulated PSCs maintain 85% of the initial PCE after 3600 h of maximum power point tracking and maintain 85% of the initial PCE after being heated at 60 °C for 3000 h. The molten salt strategy opens a new avenue for the application of evaporation in perovskite optoelectronics.     

Multifunctional Organic Potassium Salt Additives as the Efficient Defect Passivator for High-Efficiency and Stable Perovskite Solar Cells

Despite the rapid developments are achieved for perovskite solar cells (PSCs), the existence of various defects in the devices still limits the further enhancement of the power conversion efficiency (PCE) and the long-term stability of devices. Herein, the efficient organic potassium salt (OPS) of para-halogenated phenyl trifluoroborates is presented as the precursor additives to improve the performance of PSCs. Studies have shown that the 4-chlorophenyltrifluoroborate potassium salt (4-ClPTFBK) exhibits the most effective interaction with the perovskite lattice. Strong coordination between  BF₃⁻/halogen in anion and uncoordinated Pb²⁺/halide vacancies, along with the hydrogen bond between F in  BF₃⁻ and H in FA⁺ are observed. Thus, due to the synergistic contribution of the potassium and anionic groups, the high-quality perovskite film with large grain size and low defect density is achieved. As a result, the optimal devices show an enhanced efficiency of 24.50%, much higher than that of the control device (22.63%). Furthermore, the unencapsulated devices present remarkable thermal and long-term stability, maintaining 86% of the initial PCE after thermal test at 80 °C for 1000 h and 95% after storage in the air for 2460 h.     

Co-Evaporated MAPbI3 with Graded Fermi Levels Enables Highly Performing,Scalable, and Flexible p-i-n Perovskite Solar Cells

Recent progress of vapor-deposited perovskite solar cells (PSCs) has proved the feasibility of this deposition method in achieving promising photovoltaic devices. For the first time, it is probed the versatility of the co-evaporation process in creating perovskite layers customizable for different device architectures. A gradient of composition is created within the perovskite films by tuning the background chamber pressure during the growth process. This method leads to co-evaporated MAPbI₃ film with graded Fermi levels across the thickness. Here it is proved that this growth process is beneficial for p-i-n PSCs as it can guarantee a favorable energy alignment at the charge selective interfaces. Co-evaporated p-i-n PSCs, with different hole transporting layers, consistently achieve power conversion efficiency (PCE) over 20% with a champion value of 20.6%, one of the highest reported to date. The scaled-up p-i-n PSCs, with active areas of 1 and 1.96 cm², achieved the record PCEs of 19.1% and 17.2%, respectively, while the flexible PSCs reached a PCE of 19.3%. Unencapsulated PSCs demonstrate remarkable long-term stability, retaining ≈90% of their initial PCE when stored in ambient for 1000 h. These PSCs also preserve over 80% of their initial PCE after 500 h of thermal aging at 85 °C.     

Controlling the Intermediate Phase to Improve the Crystallinity and Orientation of Cs3Sb2ClxI9-x Films for Efficient Solar Cells

Lead-free 2D antimony-based halide perovskites with excellent optoelectronic properties, low toxicity, and good intrinsic stability are promising for photovoltaic devices. However, the power conversion efficiency (PCE) of antimony-based perovskite solar cells (PSCs) is still lower than 3% due to the poor crystallinity and random orientation. Herein, it is found that the Cs₃Sb₂Cl_xI_9-x films prepared by adding methylamine chloride as an additive to the precursor solution can form a mixed intermediate phase with 0D dimer phase and 2D layered phase after low pressure treatment. During the annealing process, the 0D dimer phase will completely transition to 2D layered phase due to the partial replacement of I by Cl. Compared to adding SbCl₃ directly, this method considerably increases the crystallinity of Cs₃Sb₂I_xCl_9-x films. The obtained films have a preferential orientation along the (201) direction, which is beneficial for charge carrier transportation. Consequently, the champion device shows a PCE of 3.2%, which is one of the highest efficiencies achieved for inorganic Sb-based PSCs with the n-i-p architecture to date.     

Expanded Phase Distribution in Low Average Layer-Number 2D Perovskite Films: Toward Efficient Semitransparent Solar Cells

The application of low average layer-number (〈n〉 ≤ 2) 2D perovskites in semitransparent photovoltaics (ST-PVs) has been hindered by their strong exciton binding energy and high electrical anisotropy. Here, the phase distribution is expanded fully and orderly to enable efficient charge transport in 2D (NMA)₂(MA)Pb₂I₇ (NMA: 1-naphthylmethylammonium, MA: CH₃NH₃⁺) perovskite films by regulating the sedimentation dynamics of organic cation-based colloids. Ammonium chloride is synergistically introduced to enhance the phase separation further and construct a favorable out-of-plane orientation. The wide and graded phase distribution well aligns the energy level to facilitate charge transfer. As a result, the first application of an average 〈n〉 = 2 2D perovskite is implemented in ST-PVs with visible power conversion efficiency (PCE) of 7.52% and high average visible transmittance (AVT) of 40.5%. This study offers a new candidate and an effective strategy for efficient and stable ST-PVs and is relevant to other perovskite optoelectronic devices.