Surface modified NiOx as an efficient hole transport layer in inverted perovskite solar cells

Hole transporting materials play a vital role in improving the performance of perovskite solar cells (PSCs). In this work, different concentrations of poly[bis(4-phenyl)(2, 4, 6-trimethylphenyl)amine] (PTAA) are used to modify the surface of sputtered nickel oxide (NiO_x) as hole transport layer (HTL) in inverted PSCs. After the introduction of PTAA, the roughness of the sputtered NiO_x films decreases, while the crystallinity of the perovskite layer increases. The carrier transport across the interface between the sputtered NiO_x film and the perovskite layer is significantly improved. A power conversion efficiency of 18.5% is achieved based on PTAA-modified sputtered NiO_x, exhibiting a 15.2% improvement compared to its pristine counterpart.

     

Highly Efficient and Stable Flexible Perovskite Solar Cells with Metal Oxides Nanoparticle Charge Extraction Layers

In this study, the fabrication of highly efficient and durable flexible inverted perovskite solar cells (PSCs) is reported. Presynthesized, solution‐derived NiO_x and ZnO nanoparticles films are employed at room temperature as a hole transport layer (HTL) and electron transport layer (ETL), respectively. The triple cation perovskite films are produced in a single step and for the sake of comparison, ultrasmooth and pinhole‐free absorbing layers are also fabricated using MAPbI₃ perovskite. The triple cation perovskite cells exhibit champion power conversion efficiencies (PCEs) of 18.6% with high stabilized power conversion efficiency of 17.7% on rigid glass/indium tin oxide (ITO) substrates (comparing with 16.6% PCE with 16.1% stabilized output efficiency for the flexible polyethylene naphthalate (PEN)/thin film barrier/ITO substrates). More interestingly, the durability of flexible PSC under simulation of operative condition is proved. Over 85% of the maximum stabilized output efficiency is retained after 1000 h aging employing a thin MAPbI₃ perovskite (over 90% after 500 h with a thick triple cation perovskite). This result is comparable to a similar state of the art rigid PSC and represents a breakthrough in the stability of flexible PSC using ETLs and HTLs compatible with roll to roll production speed, thanks to their room temperature processing.     

Highly Efficient p‐i‐n Perovskite Solar Cells Utilizing Novel Low‐Temperature Solution‐Processed Hole Transport Materials with Linear π‐Conjugated Structure

Alternative low‐temperature solution‐processed hole‐transporting materials (HTMs) without dopant are critical for highly efficient perovskite solar cells (PSCs). Here, two novel small molecule HTMs with linear π‐conjugated structure, 4,4′‐bis(4‐(di‐p‐toyl)aminostyryl)biphenyl (TPASBP) and 1,4′‐bis(4‐(di‐p‐toyl)aminostyryl)benzene (TPASB), are applied as hole‐transporting layer (HTL) by low‐temperature (sub‐100 °C) solution‐processed method in p‐i‐n PSCs. Compared with standard poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonic acid) (PEDOT:PSS) HTL, both TPASBP and TPASB HTLs can promote the growth of perovskite (CH₃NH₃PbI₃) film consisting of large grains and less grain boundaries. Furthermore, the hole extraction at HTL/CH₃NH₃PbI₃ interface and the hole transport in HTL are also more efficient under the conditions of using TPASBP or TPASB as HTL. Hence, the photovoltaic performance of the PSCs is dramatically enhanced, leading to the high efficiencies of 17.4% and 17.6% for the PSCs using TPASBP and TPASB as HTL, respectively, which are ≈40% higher than that of the standard PSC using PEDOT:PSS HTL.     

Graded Heterojunction Engineering for Hole‐Conductor‐Free Perovskite Solar Cells with High Hole Extraction Efficiency and Conductivity

Despite great progress in the photovoltaic conversion efficiency (PCE) of inorganic–organic hybrid perovskite solar cells (PSCs), the large‐scale application of PSCs still faces serious challenges due to the poor‐stability and high‐cost of the spiro‐OMeTAD hole transport layer (HTL). It is of great fundamental importance to rationally address the issues of hole extraction and transfer arising from HTL‐free PSCs. Herein, a brand‐new PSC architecture is designed by introducing multigraded‐heterojunction (GHJ) inorganic perovskite CsPbBr_x I_3?x layers as an efficient HTL. The grade adjustment can be achieved by precisely tuning the halide proportion and distribution in the CsPbBr_x I_3?x film to reach an optimal energy alignment of the valance and conduction band between MAPbI₃ and CsPbBr_x I_3?x . The CsPbBr_x I_3?x GHJ as an efficient HTL can induce an electric field where a valance/conduction band edge is leveraged to bend at the heterojunction interface, boosting the interfacial electron–hole splitting and photoelectron extraction. The GHJ architecture enhances the hole extraction and conduction efficiency from the MAPbI₃ to the counter electrode, decreases the recombination loss during the hole transfer, and benefits in increasing the open‐circuit voltage. The optimized HTL‐free PCS based on the GHJ architecture demonstrates an outstanding thermal stability and a significantly improved PCE of 11.33%, nearly 40% increase compared with 8.16% for pure HTL‐free devices.     

Cesium Lead Inorganic Solar Cell with Efficiency beyond 18% via Reduced Charge Recombination

Cesium‐based inorganic perovskite solar cells (PSCs) are promising due to their potential for improving device stability. However, the power conversion efficiency of the inorganic PSCs is still low compared with the hybrid PSCs due to the large open‐circuit voltage (V_OC) loss possibly caused by charge recombination. The use of an insulated shunt‐blocking layer lithium fluoride on electron transport layer SnO₂ for better energy level alignment with the conduction band minimum of the CsPbI_3‐xBr_x and also for interface defect passivation is reported. In addition, by incorporating lead chloride in CsPbI_3‐xBr_x precursor, the perovskite film crystallinity is significantly enhanced and the charge recombination in perovksite is suppressed. As a result, optimized CsPbI_3‐xBr_x PSCs with a band gap of 1.77 eV exhibit excellent performance with the best V_OC as high as 1.25 V and an efficiency of 18.64%. Meanwhile, a high photostability with a less than 6% efficiency drop is achieved for CsPbI_3‐xBr_x PSCs under continuous 1 sun equivalent illumination over 1000 h.     

Nanoscale Insights into Photovoltaic Hysteresis in Triple‐Cation Mixed‐Halide Perovskite: Resolving the Role of Polarization and Ionic Migration

Triple‐cation mixed‐halide perovskites of composition Cs_x(FA_yMA_1?y)_1?xPb(I_zBr_1?z)₃ (CsFAMA) have been reported to possess excellent photovoltaic efficiency with minimal hysteresis; in this work, nanoscale insight is shed into the roles of illumination‐induced polarization and ionic migration in photovoltaic hysteresis. By examining the concurrent evolution of ionic distribution and spontaneous polarization of CsFAMA under light illumination using dynamic‐strain‐based scanning probe microscopy, strong linear piezoelectricity arising from photoenhanced polarization is observed, while ionic migration is found to be not significantly increased by lightening. Nanoscale photocurrents are mapped under a series of biases using conductive atomic force microscopy, revealing negligible difference between forward and backward scans, and local IV curves reconstructed from principal component analysis show minimal hysteresis of just 1%. These observations at the nanoscale are confirmed in a macroscopic perovskite solar cell made of CsFAMA, exhibiting a high efficiency of 20.11% and with hysteresis index as small as 3%. Ionic migration, polarization, and photocurrent hysteresis are thus directly correlated at the nanoscale, and photoenhanced polarization in triple‐cation mixed‐halide perovskites is established, which does not contribute to the photovoltaic hysteresis.     

In Situ Real‐Time Study of the Dynamic Formation and Conversion Processes of Metal Halide Perovskite Films

Metal halide perovskite solar cells (PSCs) have advanced to the forefront of solution‐processed photovoltaic techniques and made stunning progress in power conversion efficiency (PCE). Further improvements in device performances rely on perfecting the structure and morphology of perovskite films. However, undesirable defects such as pinholes and grain boundaries are often created in film preparations due to lack of knowledge of the precise reaction mechanism. Here, in situ grazing‐incidence X‐ray diffraction (GI‐XRD) investigations are performed, facilitated by other techniques, on the formation of the widely adopted MAPbI₃ (MA = methylammonium) perovskite films from their intermediate adduct (IA) phases. The influences of solvent vapor atmospheres on MAPbI₃ films are also systematically investigated, where the dynamic conversion processes between different phases are visualized in real time. Further in situ GI‐XRD and infrared spectroscopy measurements reveal that the IA phases contain both N,N‐dimethylformamide and dimethyl sulfoxide (DMSO) as coordinating molecules. By tuning the DMSO concentration in perovskite precursors, the ideal perovskite film is formed and the best PCE is achieved for the planar MAPbI₃‐based PSCs. These findings highlight the role of IA phases and the effect of solvent atmospheres on the quality of perovskite films, providing direct insights into their growth mechanism.     

Unique 1D Cd1−xZnxS@O‐MoS2/NiOx Nanohybrids: Highly Efficient Visible‐Light‐Driven Photocatalytic Hydrogen Evolution via Integrated Structural Regulation

Development of noble‐metal‐free photocatalysts for highly efficient sunlight‐driven water splitting is of great interest. Nevertheless, for the photocatalytic H₂ evolution reaction (HER), the integrated regulation study on morphology, electronic band structures, and surface active sites of catalyst is still minimal up to now. Herein, well‐defined 1D Cd_1?xZn_xS@O‐MoS₂/NiO_x hybrid nanostructures with enhanced activity and stability for photocatalytic HER are prepared. Interestingly, the band alignments, exposure of active sites, and interfacial charge separation of Cd_1?xZn_xS@O‐MoS₂/NiO_x are optimized by tuning the Zn‐doping content as well as the growth of defect‐rich O‐MoS₂ layer and NiO_x nanoparticles, which endow the hybrids with excellent HER performances. Specifically, the visible‐light‐driven (>420 nm) HER activity of Cd_1?xZn_xS@O‐MoS₂/NiO_x with 15% Zn‐doping and 0.2 wt% O‐MoS₂ (CZ_0.15S‐0.2M‐NiO_x) in lactic acid solution (66.08 mmol h^?1 g^?1) is about 25 times that of Pt loaded CZ_0.15S, which is further increased to 223.17 mmol h^?1 g^?1 when using Na₂S/Na₂SO₃ as the sacrificial agent. Meanwhile, in Na₂S/Na₂SO₃ solution, the CZ_0.15S‐0.2M‐NiO_x sample demonstrates an apparent quantum yield of 64.1% at 420 nm and a good stability for HER under long‐time illumination. The results presented in this work can be valuable inspirations for the exploitation of advanced materials for energy‐related applications.     

Trash into Treasure: δ‐FAPbI3 Polymorph Stabilized MAPbI3 Perovskite with Power Conversion Efficiency beyond 21%

Effective passivation and stabilization of both the inside and interface of a perovskite layer are crucial for perovskite solar cells (PSCs), in terms of efficiency, reproducibility, and stability. Here, the first formamidinium lead iodide (δ‐FAPbI₃) polymorph passivated and stabilized MAPbI₃ PSCs are reported. This novel MAPbI₃/δ‐FAPbI₃ structure is realized via treating a mixed organic cation MA _x FA_{1‐ x} PbI₃ perovskite film with methylamine (MA) gas. In addition to the morphology healing, MA gas can also induce the formation of δ‐FAPbI₃ phase within the perovskite film. The in situ formed 1D δ‐FAPbI₃ polymorph behaves like an organic scaffold that can passivate the trap state, tunnel contact, and restrict organic‐cation diffusion. As a result, the device efficiency is easily boosted to 21%. Furthermore, the stability of the MAPbI₃/δ‐FAPbI₃ film is also obviously improved. This δ‐FAPbI₃ phase passivation strategy opens up a new direction of perovskite structure modification for further improving stability without sacrificing efficiency.     

Amide‐Catalyzed Phase‐Selective Crystallization Reduces Defect Density in Wide‐Bandgap Perovskites

Wide‐bandgap (WBG) formamidinium–cesium (FA‐Cs) lead iodide–bromide mixed perovskites are promising materials for front cells well‐matched with crystalline silicon to form tandem solar cells. They offer avenues to augment the performance of widely deployed commercial solar cells. However, phase instability, high open‐circuit voltage (V_oc) deficit, and large hysteresis limit this otherwise promising technology. Here, by controlling the crystallization of FA‐Cs WBG perovskite with the aid of a formamide cosolvent, light‐induced phase segregation and hysteresis in perovskite solar cells are suppressed. The highly polar solvent additive formamide induces direct formation of the black perovskite phase, bypassing the yellow phases, thereby reducing the density of defects in films. As a result, the optimized WBG perovskite solar cells (PSCs) (E_g ≈ 1.75 eV) exhibit a high V_oc of 1.23 V, reduced hysteresis, and a power conversion efficiency (PCE) of 17.8%. A PCE of 15.2% on 1.1 cm² solar cells, the highest among the reported efficiencies for large‐area PSCs having this bandgap is also demonstrated. These perovskites show excellent phase stability and thermal stability, as well as long‐term air stability. They maintain ≈95% of their initial PCE after 1300 h of storage in dry air without encapsulation.     

Morphology Control of Doped Spiro‐MeOTAD Films for Air Stable Perovskite Solar Cells

Doped 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (spiro‐MeOTAD), which acts as a hole‐transporting layer (HTL), endows perovskite solar cells (PSCs) with excellent performance. However, the intrinsically hygroscopic nature of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) dopants also aggravates the moisture instability of PSCs. In this work, the origins of the moisture instability of spiro‐MeOTAD HTLs are explored and strategies to enhance moisture resistance are proposed. After 780 h of aging in air, 52% of the initial power conversion efficiency (PCE) can be sustained by prolonging the mixing time of the precursor solution of spiro‐MeOTAD to reduce accumulated LiTFSI. In contrast, only 7% of the initial PCE remains if the precursor solution is mixed briefly. By thermally annealing an HTL to evaporate residual tBP in spiro‐MeOTAD, pinholes are completely eliminated and 65% of the initial PCE remains after the same aging time. In this study, the significance of the initial morphology of spiro‐MeOTAD HTLs on device stability is analyzed and strategies based on physical morphology for controlling PSC moisture instability induced by HTL dopants are developed.     

Efficient and Stable Inverted Perovskite Solar Cells Incorporating Secondary Amines

Large‐bandgap perovskites offer a route to improve the efficiency of energy capture in photovoltaics when employed in the front cell of perovskite–silicon tandems. Implementing perovskites as the front cell requires an inverted (p–i–n) architecture; this architecture is particularly effective at harnessing high‐energy photons and is compatible with ionic‐dopant‐free transport layers. Here, a power conversion efficiency of 21.6% is reported, the highest among inverted perovskite solar cells (PSCs). Only by introducing a secondary amine into the perovskite structure to form MA_1?xDMA_xPbI₃ (MA is methylamine and DMA is dimethylamine) are defect density and carrier recombination suppressed to enable record performance. It is also found that the controlled inclusion of DMA increases the hydrophobicity and stability of films in ambient operating conditions: encapsulated devices maintain over 80% of their efficiency following 800 h of operation at the maximum power point, 30 times longer than reported in the best prior inverted PSCs. The unencapsulated devices show record operational stability in ambient air among PSCs.     

Highly Efficient and Stable GABr-Modified Ideal-Bandgap (1.35 eV) Sn/Pb Perovskite Solar Cells Achieve 20.63% Efficiency with a Record Small Voc Deficit of 0.33 V

1.5–1.6 eV bandgap Pb-based perovskite solar cells (PSCs) with 30–31% theoretical efficiency limit by the Shockley–Queisser model achieve 21–24% power conversion efficiencies (PCEs). However, the best PCEs of reported ideal-bandgap (1.3–1.4 eV) Sn–Pb PSCs with a higher 33% theoretical efficiency limit are <18%, mainly because of their large open-circuit voltage (V_oc) deficits (>0.4 V). Herein, it is found that the addition of guanidinium bromide (GABr) can significantly improve the structural and photoelectric characteristics of ideal-bandgap (≈1.34 eV) Sn–Pb perovskite films. GABr introduced in the perovskite films can efficiently reduce the high defect density caused by Sn²⁺ oxidation in the perovskite, which is favorable for facilitating hole transport, decreasing charge-carrier recombination, and reducing the V_oc deficit. Therefore, the best PCE of 20.63% with a certificated efficiency of 19.8% is achieved in 1.35 eV PSCs, along with a record small V_oc deficit of 0.33 V, which is the highest PCE among all values reported to date for ideal-bandgap Sn–Pb PSCs. Moreover, the GABr-modified PSCs exhibit significantly improved environmental and thermal stability. This work represents a noteworthy step toward the fabrication of efficient and stable ideal-bandgap PSCs.     

Reducing Hysteresis and Enhancing Performance of Perovskite Solar Cells Using Low‐Temperature Processed Y‐Doped SnO2 Nanosheets as Electron Selective Layers

Despite the rapid increase of efficiency, perovskite solar cells (PSCs) still face some challenges, one of which is the current–voltage hysteresis. Herein, it is reported that yttrium‐doped tin dioxide (Y‐SnO₂) electron selective layer (ESL) synthesized by an in situ hydrothermal growth process at 95 °C can significantly reduce the hysteresis and improve the performance of PSCs. Comparison studies reveal two main effects of Y doping of SnO₂ ESLs: (1) it promotes the formation of well‐aligned and more homogeneous distribution of SnO₂ nanosheet arrays (NSAs), which allows better perovskite infiltration, better contacts of perovskite with SnO₂ nanosheets, and improves electron transfer from perovskite to ESL; (2) it enlarges the band gap and upshifts the band energy levels, resulting in better energy level alignment with perovskite and reduced charge recombination at NSA/perovskite interfaces. As a result, PSCs using Y‐SnO₂ NSA ESLs exhibit much less hysteresis and better performance compared with the cells using pristine SnO₂ NSA ESLs. The champion cell using Y‐SnO₂ NSA ESL achieves a photovoltaic conversion efficiency of 17.29% (16.97%) when measured under reverse (forward) voltage scanning and a steady‐state efficiency of 16.25%. The results suggest that low‐temperature hydrothermal‐synthesized Y‐SnO₂ NSA is a promising ESL for fabricating efficient and hysteresis‐less PSC.     

Highly Efficient Nonfullerene Polymer Solar Cells Enabled by a Copper(I) Coordination Strategy Employing a 1,3,4‐Oxadiazole‐Containing Wide‐Bandgap Copolymer Donor

A novel wide‐bandgap copolymer of PBDT‐ODZ based on benzo[1,2‐b:4,5‐b′ ]dithiophene (BDT) and 1,3,4‐oxadiazole (ODZ) blocks is developed for efficient nonfullerene polymer solar cells (NF‐PSCs). PBDT‐ODZ exhibits a wide bandgap of 2.12 eV and a low‐lying highest occupied molecular orbital (HOMO) level of ?5.68 eV, which could match well with the low‐bandgap acceptor of 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone)‐5,5,11,11‐tetrakis(4‐hexylthienyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]‐dithiophene (ITIC‐Th), inducing a good complementary absorption from 300 to 800 nm and a minimal HOMO level offset (0.1 eV). The PBDT‐ODZ:ITIC‐Th devices exhibit a large open‐circuit voltage (V_oc) of 1.08 eV and a low energy loss (E_loss) of 0.50 eV, delivering a high power conversion efficiency (PCE) of 10.12%. By adding a small amount of copper(I) iodide (CuI) as an additive to form coordination complexes in the active blends, much higher device performances are achieved due to the improved absorption and crystallinity. After incorporating 4% of CuI, the PCE is elevated to 12.34%, with a V_oc of 1.06 V, a J_sc of 17.1 mA cm^?2 and a fill factor of 68.1%. This work not only provides a novel oxadiazole‐containing wide‐bandgap polymeric donor candidate for high‐performance NF‐PSCs but also presents an efficient morphology‐optimization approach to elevate the PCE of NF‐PSCs for future practical applications.     

Design for Highly Piezoelectric and Visible/Near‐Infrared Photoresponsive Perovskite Oxides

Defect‐engineered perovskite oxides that exhibit ferroelectric and photovoltaic properties are promising multifunctional materials. Though introducing gap states by transition metal doping on the perovskite B‐site can obtain low bandgap (i.e., 1.1–3.8 eV), the electrically leaky perovskite oxides generally lose piezoelectricity mainly due to oxygen vacancies. Therefore, the development of highly piezoelectric ferroelectric semiconductor remains challenging. Here, inspired by point‐defect‐mediated large piezoelectricity in ferroelectrics especially at the morphotropic phase boundary (MPB) region, an efficient strategy is proposed by judiciously introducing the gap states at the MPB where defect‐induced local polar heterogeneities are thermodynamically coupled with the host polarization to simultaneously achieve high piezoelectricity and low bandgap. A concrete example, Ni²⁺‐mediated (1–x)Na_0.5Bi_0.5TiO₃‐xBa(Ti_0.5Ni_0.5)O_3–δ (x = 0.02–0.08) composition is presented, which can show excellent piezoelectricity and unprecedented visible/near‐infrared light absorption with a lowest ever bandgap ≈0.9 eV at room temperature. In particular, the MPB composition x = 0.05 shows the best ferroelectricity/piezoelectricity (d₃₃ = 151 pC N^–1, Pr = 31.2 μC cm^–2) and a largely enhanced photocurrent density approximately two orders of magnitude higher compared with classic ferroelectric (Pb,La)(Zr,Ti)O₃. This research provides a new paradigm for designing highly piezoelectric and visible/near‐infrared photoresponsive perovskite oxides for solar energy conversion, near‐infrared detection, and other multifunctional applications.     

Reproducible resistance switching of defect-engineered NiOx with metallic Nb impurity

The effect of Nb doping on the resistance switching characteristics of NiO_x films was investigated. Pt/Nb-doped NiO_x/Pt metal-insulator-metal stacks were fabricated using NiO_x films with various Nb contents sputtered by reactive dc magnetron sputtering. The resistance switching behaviors of the metal-insulator-metal stacks were then examined in conjunction with a study on the physical properties such as the chemical bonding of NiO_x films.Nb doping of NiO_x at a T_dep of 400 °C and an O₂ partial pressure of 5% resulted in an improved endurance of SET/RESET processes with a narrower distribution of V_SET, and a larger memory window compared to un-doped NiO_x films. NiO_x with 5.47% Nb deposited at an O₂ partial pressure of 15% showed bistable resistance switching behavior while undoped NiO_x material, deposited under the same condition did not. A study of the chemical bonding states by X-ray photoelectron spectroscopy showed that the Nb-doping of NiO_x films produced an increase in the density of Ni⁰ and a reduction in the density of Ni³⁺, compared to corresponding values for undoped NiO_x films deposited under the same condition. The resistive switching behavior of NiO_x was enhanced by defect engineering with metal impurity with different oxidation valence.     

Achieving Large‐Area Planar Perovskite Solar Cells by Introducing an Interfacial Compatibilizer

Despite the recent unprecedented increase in the power conversion efficiencies (PCEs) of small‐area devices (≤0.1 cm²), the PCEs deteriorate drastically for PSCs of larger areas because of the incomplete film coverage caused by the dewetting of the hydrophilic perovskite precursor solutions on the hydrophobic organic charge‐transport layers (CTLs). Here, an innovative method of fabricating scalable PSCs on all types of organic CTLs is reported. By introducing an amphiphilic conjugated polyelectrolyte as an interfacial compatibilizer, fabricating uniform perovskite films on large‐area substrates (18.4 cm²) and PSCs with the total active area of 6 cm² (1 cm² × 6 unit cells) via a single‐turn solution process is successfully demonstrated. All of the unit cells exhibit highly uniform PCEs of 16.1 ± 0.9% (best PCE of 17%), which is the highest value for printable PSCs with a total active area larger than 1 cm².     

Insights about the Absence of Rb Cation from the 3D Perovskite Lattice: Effect on the Structural,Morphological, and Photophysical Properties and Photovoltaic Performance

Efficiencies >20% are obtained from the perovskite solar cells (PSCs) employing Cs⁺ and Rb⁺ based perovskite compositions; therefore, it is important to understand the effect of these inorganic cations specifically Rb⁺ on the properties of perovskite structures. Here the influence of Cs⁺ and Rb⁺ is elucidated on the structural, morphological, and photophysical properties of perovskite structures and the photovoltaic performances of resulting PSCs. Structural, photoluminescence (PL), and external quantum efficiency studies establish the incorporation of Cs⁺ (x < 10%) but amply rule out the possibility of Rb‐incorporation into the MAPbI₃ (MA = CH₃NH₃ ⁺) lattice. Moreover, morphological studies and time‐resolved PL show that both Cs⁺ and Rb⁺ detrimentally affect the surface coverage of MAPbI₃ layers and charge‐carrier dynamics, respectively, by influencing nucleation density and by inducing nonradiative recombination. In addition, differential scanning calorimetry shows that the transition from orthorhombic to tetragonal phase occurring around 160 K requires more thermal energy for the Cs‐containing MAPbI₃ systems compared to the pristine MAPbI₃. Investigation including mixed halide (I/Br) and mixed cation A‐cation based compositions further confirms the absence of Rb⁺ from the 3D‐perovskite lattice. The fundamental insights gained through this work will be of great significance to further understand highly promising perovskite compositions.     

Precise Control of Crystallization and Phase-Transition with Green Anti-Solvent in Wide-Bandgap Perovskite Solar Cells with Open-Circuit Voltage Exceeding 1.25 V

Wide-bandgap perovskite solar cells (PSCs) have attracted a lot of attention due to their application in tandem solar cells. However, the open-circuit voltage (V_OC) of wide-bandgap PSCs is dramatically limited by high defect density existing at the interface and bulk of the perovskite film. Here, an anti-solvent optimized adduct to control perovskite crystallization strategy that reduces nonradiative recombination and minimizes V_OC deficit is proposed. Specifically, an organic solvent with similar dipole moment, isopropanol (IPA) is added into ethyl acetate (EA) anti-solvent, which is beneficial to form PbI₂ adducts with better crystalline orientation and direct formation of α-phase perovskite. As a result, EA-IPA (7-1) based 1.67 eV PSCs deliver a power conversion efficiency of 20.06% and a V_OC of 1.255 V, which is one of the remarkable values for wide-bandgap around 1.67 eV. The findings provide an effective strategy for controlling crystallization to reduce defect density in PSCs.