Why are Hot Holes Easier to Extract than Hot Electrons from Methylammonium Lead Iodide Perovskite?

Charge‐carriers photoexcited above a semiconductor's bandgap rapidly thermalize to the band‐edge. The cooling of these difficult to collect “hot” carriers caps the available photon energy that solar cells–including efficient perovskite solar cells–may utilize. Here, the dynamics and efficiency of hot carrier extraction from MAPbI₃ (MA = methylammonium) perovskite by spiro‐OMeTAD (a hole‐transporting layer) and TiO₂ (an electron‐transporting layer) are investigated and explained using both ultrafast electronic spectroscopy and theoretical modeling. Time‐resolved spectroscopy reveals a quasi‐equilibrium distribution of hot carriers forming upon excess‐energy excitation of the perovskite–a distribution largely unaffected by the presence of TiO₂. In contrast, the quasi‐equilibrium distribution of hot carriers is virtually nonexistent when spiro‐OMeTAD is present, which is indicative of efficient hot hole extraction at the interface of MAPbI₃. Density functional theory calculations predict that deep energy‐levels of MAPbI₃ exhibit electronically delocalized character, with significant overlap with the localized valence band charge of the spiro‐OMeTAD molecules lying on the surface of MAPbI₃. Consequently, hot holes are easily extracted from the deep energy‐levels of MAPbI₃ by spiro‐OMeTAD. These findings uncover the origins of efficient hot hole extraction in perovskites and offer a practical blueprint for optimizing solar cell interlayers to enable hot carrier utilization.     

Effect of Electron‐Transport Material on Light‐Induced Degradation of Inverted Planar Junction Perovskite Solar Cells

This paper presents a systematic study of the influence of electron‐transport materials on the operation stability of the inverted perovskite solar cells under both laboratory indoor and the natural outdoor conditions in the Negev desert. It is shown that all devices incorporating a Phenyl C₆₁ Butyric Acid Methyl ester ([60]PCBM) layer undergo rapid degradation under illumination without exposure to oxygen and moisture. Time‐of‐flight secondary ion mass spectrometry depth profiling reveals that volatile products from the decomposition of methylammonium lead iodide (MAPbI₃) films diffuse through the [60]PCBM layer, go all the way toward the top metal electrode, and induce its severe corrosion with the formation of an interfacial AgI layer. On the contrary, alternative electron‐transport material based on the perylendiimide derivative provides good isolation for the MAPbI₃ films preventing their decomposition and resulting in significantly improved device operation stability. The obtained results strongly suggest that the current approach to design inverted perovskite solar cells should evolve with respect to the replacement of the commonly used fullerene‐based electron‐transport layers with other types of materials (e.g., functionalized perylene diimides). It is believed that these findings pave a way toward substantial improvements in the stability of the perovskite solar cells, which are essential for successful commercialization of this photovoltaic technology.     

Ultrathin Perovskite Monocrystals Boost the Solar Cell Performance

Grains and grain boundaries play key roles in determining halide perovskite‐based optoelectronic device performance. Halide perovskite monocrystalline solids with large grains, smaller grain boundaries, and uniform surface morphology improve charge transfer and collection, suppress recombination loss, and thus are highly favorable for developing efficient solar cells. To date, strategies of synthesizing high‐quality thin monocrystals (TMCs) for solar cell applications are still limited. Here, by combining the antisolvent vapor‐assisted crystallization and space‐confinement strategies, high‐quality millimeter sized TMCs of methylammonium lead iodide (MAPbI₃) perovskites with controlled thickness from tens of nanometers to several micrometers have been fabricated. The solar cells based on these MAPbI₃ TMCs show power conversion efficiency (PCE) of 20.1% which is significantly improved compared to their polycrystalline counterparts (PCE) of 17.3%. The MAPbI₃ TMCs show large grain size, uniform surface morphology, high hole mobility (up to 142 cm² V^?1 s^?1), as well as low trap (defect) densities. These properties suggest that TMCs can effectively suppress the radiative and nonradiative recombination loss, thus provide a promising way for maximizing the efficiency of perovskite solar cells.     

Impact of PbI2 Passivation and Grain Size Engineering in CH3NH3PbI3 Solar Absorbers as Revealed by Carrier‐Resolved Photo‐Hall Technique

With power conversion efficiencies now exceeding 25%, hybrid perovskite solar cells require deeper understanding of defects and processing to further approach the Shockley‐Queisser limit. One approach for processing enhancement and defect reduction involves additive engineering—, e.g., addition of MASCN (MA = methylammonium) and excess PbI₂ have been shown to modify film grain structure and improve performance. However, the underlying impact of these additives on transport and recombination properties remains to be fully elucidated. In this study, a newly developed carrier‐resolved photo‐Hall (CRPH) characterization technique is used that gives access to both majority and minority carrier properties within the same sample and over a wide range of illumination conditions. CRPH measurements on n‐type MAPbI₃ films reveal an order of magnitude increase in carrier recombination lifetime and electron density for 5% excess PbI₂ added to the precursor solution, with little change noted in electron and hole mobility values. Grain size variation (120–2100 nm) and MASCN addition induce no significant change in carrier‐related parameters considered, highlighting the benign nature of the grain boundaries and that excess PbI₂ must predominantly passivate bulk defects rather than defects situated at grain boundaries. This study offers a unique picture of additive impact on MAPbI₃ optoelectronic properties as elucidated by the new CRPH approach.     

New Strategy for Two‐Step Sequential Deposition: Incorporation of Hydrophilic Fullerene in Second Precursor for High‐Performance p‐i‐n Planar Perovskite Solar Cells

In p‐i‐n planar perovskite solar cells (pero‐SCs) based on methylammonium lead iodide (MAPbI₃) perovskite, high‐quality MAPbI₃ film, perfect interfacial band alignment and efficient charge extracting ability are critical for high photovoltaic performance. In this work, a hydrophilic fullerene derivative [6,6]‐phenyl‐C₆₁‐butyric acid‐(3,4,5‐tris(2‐(2‐(2‐methoxyethoxy)ethoxy)ethoxy)phenyl)methanol ester (PCBB‐OEG) is introduced as additive in the methylammonium iodide precursor solution in the preparation of MAPbI₃ perovskite film by two‐step sequential deposition method, and obtained a top‐down gradient distribution with an ultrathin top layer of PCBB‐OEG. Meanwhile, a high‐quality perovskite film with high crystallinity, less trap‐states, and dense‐grained uniform morphology can well grow on both hydrophilic (poly(3,4‐ethylenedioxythiophene)/poly(styrenesulfonic acid)) and hydrophobic (polytriarylamine, PTAA) hole transport layers. When the PCBB‐OEG‐containing perovskite film (pero‐0.1) is prepared in a p‐i‐n planar pero‐SC with the configuration of ITO/PTAA/pero‐0.1/[6,6]‐phenyl‐C₆₁‐butyric acid methyl ester/Al, the device delivers a promising power conversion efficiency (PCE) of 20.2% without hysteresis, which is one of the few PCE over 20% for the p‐i‐n planar pero‐SCs. Importantly, the pero‐0.1‐based device shows an excellent stability that can retain 98.4% of its initial PCE after being exposed for 300 h under ambient atmosphere with a high humidity, and the flexible pero‐SCs based on pero‐0.1 also demonstrate a promising PCE of 18.1%.     

Highly Efficient and Stable Solar Cells with 2D MA3Bi2I9/3D MAPbI3 Heterostructured Perovskites

Organic–inorganic hybrid lead halide perovskites are emerging as highly promising candidates for highly efficient thin film photovoltaics due to their excellent optoelectronic properties and low‐temperature process capability. However, the long‐term stability in ambient air still is a key issue limiting their further practical applications. Herein, the enhancement of both performance and stability of perovskite solar cells is reported by employing 2D and 3D heterostructured perovskite films with unique nanoplate/nanocrystalline morphology. The 2D/3D heterostructured perovskites combine advantages of the high‐performance lead‐based perovskite 3D CH₃NH₃PbI₃ (MAPbI₃) and the air‐stable bismuth‐based quasi‐perovskite 2D MA₃Bi₂I₉. In the 2D/3D heterostructure, the hydrophobic MA₃Bi₂I₉ platelets vertically situate between the MAPbI₃ grains, forming a lattice‐like structure to tightly enclose the 3D MAPbI₃ perovskite grains. The solar cell based on the optimal 2D/3D (9.2%) heterostructured film achieves a high efficiency of 18.97%, with remarkably reduced hysteresis and significantly improved stability. The work demonstrates that construction of 2D/3D heterostructured films by hybridizing different species of perovskite materials is a feasible way to simultaneously enhance both efficiency and stability of perovskite solar cells.     

Spontaneously Self‐Assembly of a 2D/3D Heterostructure Enhances the Efficiency and Stability in Printed Perovskite Solar Cells

As perovskite solar cells (PSCs) are highly efficient, demonstration of high‐performance printed devices becomes important. 2D/3D heterostructures have recently emerged as an attractive way to relieving the film inhomogeneity and instability in perovskite devices. In this work, a 2D/3D ensemble with 2D perovskites self‐assembled atop 3D methylammonium lead triiodide (MAPbI₃) via a one‐step printing process is shown. A clean and flat interface is observed in the 2D/3D bilayer heterostructure for the first time. The 2D perovskite capping layer significantly suppresses nonradiative charge recombination, resulting in a marked increase in open‐circuit voltage (V_OC) of the devices by up to 100 mV. An ultrahigh V_OC of 1.20 V is achieved for MAPbI₃ PSCs, corresponding to 91% of the Shockley–Queisser limit. Moreover, notable enhancement in light, thermal, and moisture stability is obtained as a result of the protective barrier of the 2D perovskites. These results suggest a viable approach for scalable fabrication of highly efficient perovskite solar cells with enhanced environmental stability.     

Effect of Cation Composition on the Mechanical Stability of Perovskite Solar Cells

Photoactive perovskite semiconductors are highly tunable, with numerous inorganic and organic cations readily incorporated to modify optoelectronic properties. However, despite the importance of device reliability and long service lifetimes, the effects of various cations on the mechanical properties of perovskites are largely overlooked. In this study, the cohesion energy of perovskites containing various cation combinations of methylammonium, formamidinium, cesium, butylammonium, and 5‐aminovaleric acid is reported. A trade‐off is observed between the mechanical integrity and the efficiency of perovskite devices. High efficiency devices exhibit decreased cohesion, which is attributed to reduced grain sizes with the inclusion of additional cations and PbI₂ additives. Microindentation hardness testing is performed to estimate the fracture toughness of single‐crystal perovskite, and the results indicated perovskites are inherently fragile, even in the absence of grain boundaries and defects. The devices found to have the highest fracture energies are perovskites infiltrated into a porous TiO₂/ZrO₂/C triple layer, which provide extrinsic reinforcement and shielding for enhanced mechanical and chemical stability.     

Fabrication of Efficient and Stable CsPbI3 Perovskite Solar Cells through Cation Exchange Process

Inorganic lead halide perovskites have attracted attention due to their tolerance to higher processing temperature and higher bandgap suitable for tandem solar cell application. Not only do they improve cell stability and efficiency, they also reveal many interesting and un‐anticipated material qualities. This work reports a simple cation exchange growth (CEG) method for fabricating inorganic high‐quality cesium lead iodide (CsPbI₃) by adding methylammonium iodide (MAI) additive in the precursor. X‐ray diffraction results reveal a multi‐stage film formation process whereby i) MAPbI₃ perovskite first formed that acts as a perovskite template for ii) subsequent ion exchange whereby the MA⁺ ions in the MAPbI₃ are replaced by Cs⁺ (as temperature ramps up) and iii) form g‐phase perovskite CsPbI₃. Optical microscopy, photoluminescence, and electrical characterizations reveal that the CEG process produces high‐quality film with better absorption, uniform and dense film with better interface, lower defects, and better stability. Using the CEG approach, the power conversion efficiency of the best CsPbI₃ solar cell is significantly increased up to 14.1% for the device fabricated using 1.0 m MAI additive. The outcome is beneficial for further improvement of inorganic perovskite solar cells and their application in perovskite‐silicon tandem devices.     

Role of Microstructure in Oxygen Induced Photodegradation of Methylammonium Lead Triiodide Perovskite Films

This paper investigates the impact of microstructure on the degradation rate of methylammonium lead triiodide (MAPbI₃) perovskite films upon exposure to light and oxygen. By comparing the oxygen induced degradation of perovskite films of different microstructure–fabricated using either a lead acetate trihydrate precursor or a solvent engineering technique–it is demonstrated that films with larger and more uniform grains and better electronic quality show a significantly reduced degradation compared to films with smaller, more irregular grains. The effect of degradation on the optical, compositional, and microstructural properties of the perovskite layers is characterized and it is demonstrated that oxygen induced degradation is initiated at the layer surface and grain boundaries. It is found that under illumination, irreversible degradation can occur at oxygen levels as low as 1%, suggesting that degradation can commence already during the device fabrication stage. Finally, this work establishes that improved thin‐film microstructure, with large uniform grains and a low density of defects, is a prerequisite for enhanced stability necessary in order to make MAPbI₃ a promising long lived and low cost alternative for future photovoltaic applications.     

Synergistic Crystal and Interface Engineering for Efficient and Stable Perovskite Photovoltaics

The presence of bulk and surface defects in perovskite light harvesting materials limits the overall efficiency of perovskite solar cells (PSCs). The formation of such defects is suppressed by adding methylammonium chloride (MACl) as a crystallization aid to the precursor solution to realize high‐quality, large‐grain triple A‐cation perovskite films and that are combined with judicious engineering of the perovskite interface with the electron and hole selective contact materials. A planar SnO₂/TiO₂ double layer oxide is introduced to ascertain fast electron extraction and the surface of the perovskite facing the hole conductor is treated with iodine dissolved in isopropanol to passivate surface trap states resulting in a retardation of radiationless carrier recombination. A maximum solar to electric power conversion efficiency (PCE) of 21.65% and open circuit photovoltage (V_oc) of ≈1.24 V with only ≈370 mV loss in potential with respect to the band gap are achieved, by applying these modifications. Additionally, the defect healing enhances the operational stability of the devices that retain 96%, 90%, and 85% of their initial PCE values after 500 h under continuously light illumination at 20, 50, and 65 °C, respectively, demonstrating one of the most stable planar PSCs reported so far.     

Nitrogen Soaking Promotes Lattice Recovery in Polycrystalline Hybrid Perovskites

On the basis of experiment and theory, a general paradigm is drawn that reconsiders N₂ not simply being an inert species but rather an effective healing gas molecule if entering a methylammonium lead iodide (MAPbI₃) layer. Nitrogen is soaked into polycrystalline MAPbI₃ via a postdeposition mild thermal treatment under slightly overpressure conditions to promote its diffusion across the whole layer. A significant reduction of radiative recombination and a concurrent increase of light absorption, with a maximum benefit at 80 °C, are observed. Concomitantly, the current of holes drawn from the surfaces with nanometer resolution through a biased tip is raised by a factor of 3 under N₂. This is framed by a reduction of the barrier for carrier extraction. The achieved improvements are linked to a nitrogen‐assisted recovery of intrinsic lattice disorder at the grain shells along with a simultaneous stabilization of undercoordinated Pb²⁺ and MA⁺ cations through weak electrostatic interactions. Defect mitigation under N₂ is reinforced in comparison to the benchmark behavior under argon. It is additionally unveiled that surface stabilization through N₂ is morphology‐independent and thus can be applied after any preparation procedure. Such simple and low‐cost strategy can complement other stabilizing solutions for perovskite solar cells or light‐emitting diode engineering.     

Discerning the Surface and Bulk Recombination Kinetics of Organic–Inorganic Halide Perovskite Single Crystals

Organic–inorganic halide perovskite single crystals possess many outstanding properties conducive for photovoltaic and optoelectronic applications. However, a clear photophysics picture is still elusive, particularly, their surface and bulk photophysics are inexorably convoluted by the spectral absorbance, defects, coexisting photoexcited species, etc. In this work, an all‐optical study is presented that clearly distinguishes the surface kinetics from those of the bulk in the representative methylammonium‐lead bromide (MAPbBr₃) and ‐lead iodide (MAPbI₃) single crystals. It is found that the bulk recombination lifetime of the MAPbBr₃ single crystal is shortened significantly by approximately one to two orders (i.e., from ≈34 to ≈1 ns) at the surface with a surface recombination velocity of around 6.7 × 10³ cm s^?1. The surface trap density is estimated to be around 6.0 × 10¹⁷ cm^?3, which is two orders larger than that of the bulk (5.8 × 10¹⁵ cm^?3). Correspondingly, the diffusion length of the surface excited species is ≈130–160 nm, which is considerably reduced compared to the bulk value of ≈2.6–4.3 μm. Furthermore, the surface region has a wider bandgap that possibly arises from the strong lattice deformation. The findings provide new insights into the intrinsic photophysics essential for single crystal perovskite photovoltaics and optoelectronic devices.     

The Synergism of DMSO and Diethyl Ether for Highly Reproducible and Efficient MA0.5FA0.5PbI3 Perovskite Solar Cells

Composition and film quality of perovskite are crucial for the further improvement of perovskite solar cells (PSCs), including efficiency, reproducibility, and stability. Here, it is demonstrated that by simply mixing 50% of formamidinium (FA⁺) into methylammonium lead iodide (MAPbI₃), a highly crystalline, stable phase, and compact, polycrystalline grain morphology perovskite is formed by using a solvent‐mediated phase transformation process via the synergism of dimethyl sulfoxide and diethyl ether, which shows long carrier lifetime, low trap state density, and a record certified 21.8% power conversion efficiency (PCE) in pure‐iodide, alkaline‐metal‐free MA_0.5FA_0.5PbI₃ perovskite‐based PSCs. These PSCs show very high operational stability, with 85% PCE retention upon 1000 h 1 Sun intensity illumination. A 17.33% PCE module (6.5 × 7 cm²) is also demonstrated, attesting to the scalability of such devices.     

Phase Segregation Enhanced Ion Movement in Efficient Inorganic CsPbIBr2 Solar Cells

Organic–inorganic hybrid perovskite solar cells with mixed cations and mixed halides have achieved impressive power conversion efficiency of up to 22.1%. Phase segregation due to the mixed compositions has attracted wide concerns, and their nature and origin are still unclear. Some very useful analytical techniques are controversial in microstructural and chemical analyses due to electron beam‐induced damage to the “soft” hybrid perovskite materials. In this study photoluminescence, cathodoluminescence, and transmission electron microscopy are used to study charge carrier recombination and retrieve crystallographic and compositional information for all‐inorganic CsPbIBr₂ films on the nanoscale. It is found that under light and electron beam illumination, “iodide‐rich” CsPbI_{(1+x )}Br_{(2?x )} phases form at grain boundaries as well as segregate as clusters inside the film. Phase segregation generates a high density of mobile ions moving along grain boundaries as ion migration “highways.” Finally, these mobile ions can pile up at the perovskite/TiO₂ interface resulting in formation of larger injection barriers, hampering electron extraction and leading to strong current density–voltage hysteresis in the polycrystalline perovskite solar cells. This explains why the planar CsPbIBr₂ solar cells exhibit significant hysteresis in efficiency measurements, showing an efficiency of up to 8.02% in the reverse scan and a reduced efficiency of 4.02% in the forward scan, and giving a stabilized efficiency of 6.07%.     

Ionic Reactivity at Contacts and Aging of Methylammonium Lead Triiodide Perovskite Solar Cells

Hybrid lead halide perovskites have reached very large solar to electricity power conversion efficiencies, in some cases exceeding 20%. The most extensively used perovskite‐based solar cell configuration comprises CH₃NH₃PbI₃ (MAPbI₃) in combination with electron (TiO₂) and hole 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9‐spiro‐bifluorene (spiro‐OMeTAD) selective contacts. The recognition that the solar cell performance is heavily affected by time scale of the measurement and preconditioning procedures has raised many concerns about the stability of the device and reliability for long‐time operation. Mechanisms at contacts originate observable current–voltage distortions. Two types of reactivity sources have been identified here: (i) weak Ti–I–Pb bonds that facilitate interfacial accommodation of moving iodine ions. This interaction produces a highly reversible capacitive current originated at the TiO₂/MAPbI₃ interface, and it does not alter steady‐state photovoltaic features. (ii) An irreversible redox peak only observable after positive poling at slow scan rates. It corresponds to the chemical reaction between spiro‐OMeTAD⁺ and migrating I^? which progressively reduces the hole transporting material conductivity and deteriorates solar cell performance.     

Effect of High Dipole Moment Cation on Layered 2D Organic–Inorganic Halide Perovskite Solar Cells

Layered 2D organic–inorganic hybrid perovskite is appearing as a rising star in the photovoltaic field, thanks to its superior moisture resistance by the organic spacer cations. Unfortunately, these cations lead to high exciton binding energy in the 2D perovskites, which suffers from lower efficiency in the devices. It thus requires a clear criterion to select/design appropriate organic spacer cations to improve the device efficiency based on this class of materials. Here, 2,2,2‐trifluoroethylamine (F₃EA⁺) is introduced to combine with butylammonium (BA⁺) cations as mixed spacers. While BA⁺ enables self‐assembly of 2D perovskite crystals by van der Waals interaction, the introduction of F₃EA⁺ spacers with a high dipole moment suppress nonradiative recombination and promote separation of photogenerated electron–hole pairs by taking the advantage of electronegativity of fluorine. The resultant solar cells based on [(BA)_1–x(F₃EA)_x]₂(MA)₃Pb₄I₁₃ exhibit substantially increased open circuit voltage and fill factor compared with that of (BA)₂(MA)₃Pb₄I₁₃. The champion [(BA)_0.94(F₃EA)_0.06]₂(MA)₃Pb₄I₁₃ solar cell yields a power conversion efficiency of 12.51%, which is among the best performances so far. These findings suggest an effective strategy to design organic spacer cations in layered perovskite for solar cells and other optoelectronic applications.     

Direct Evidence of Ion Diffusion for the Silver‐Electrode‐Induced Thermal Degradation of Inverted Perovskite Solar Cells

Perovskite solar cells (PSCs) have recently demonstrated high efficiencies of over 22%, but the thermal stability is still a major challenge for commercialization. In this work, the thermal degradation process of the inverted structured PSCs induced by the silver electrode is thoroughly investigated. Elemental depth profiles indicate that iodide and methylammonium ions diffuse through the electron‐trasnporting layer and accumulate at the Ag inner surface. The driving force of forming AgI then facilitates the ions extraction. Variations on the morphology and current mapping of the MAPbI₃ thin films upon thermal treatment reveal that the loss of ions occurs at the grain boundaries and leads to the reconstruction of grain domains. Consequently, the deteriorated MAPbI₃ thin film, the poor electron extraction, and the generation of AgI barrier result in the degradation of efficiencies. These direct evidences provide in‐depth understanding of the effect of thermal stress on the devices, offering both experimental support and theoretical guidance for the improvement on the thermal stability of the inverted PSCs.     

Inorganic CsPb1−xSnxIBr2 for Efficient Wide‐Bandgap Perovskite Solar Cells

Recently, the stability of organic–inorganic perovskite thin films under thermal, photo, and moisture stresses has become a major concern for further commercialization due to the high volatility of the organic cations in the prototype perovskite composition (CH₃NH₃PbI₃). All inorganic cesium (Cs) based perovskite is an alternative to avoid the release or decomposition of organic cations. Moreover, substituting Pb with Sn in the organic–inorganic lead halide perovskites has been demonstrated to narrow the bandgap to 1.2–1.4 eV for high‐performance perovskite solar cells. In this work, a series of CsPb_1?xSn_xIBr₂ perovskite alloys via one‐step antisolvent method is demonstrated. These perovskite films present tunable bandgaps from 2.04 to 1.64 eV. Consequently, the CsPb_0.75Sn_0.25IBr₂ with homogeneous and densely crystallized morphology shows a remarkable power conversion efficiency of 11.53% and a high V_oc of 1.21 V with a much improved phase stability and illumination stability. This work provides a possibility for designing and synthesizing novel inorganic halide perovskites as the next generation of photovoltaic materials.     

Spontaneous Interface Ion Exchange: Passivating Surface Defects of Perovskite Solar Cells with Enhanced Photovoltage

Interface engineering is of great concern in photovoltaic devices. For the solution‐processed perovskite solar cells, the modification of the bottom surface of the perovskite layer is a challenge due to solvent incompatibility. Herein, a Cl‐containing tin‐based electron transport layer; SnO_x‐Cl, is designed to realize an in situ, spontaneous ion‐exchange reaction at the interface of SnO_x‐Cl/MAPbI₃. The interfacial ion rearrangement not only effectively passivates the physical contact defects, but, at the same time, the diffusion of Cl ions in the perovskite film also causes longitudinal grain growth and further reduces the grain boundary density. As a result, an efficiency of 20.32% is achieved with an extremely high open‐circuit voltage of 1.19 V. This versatile design of the underlying carrier transport layer provides a new way to improve the performance of perovskite solar cells and other optoelectronic devices.