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A lead‐free hybrid double perovskite, (i‐PA)₂AgBiCsBr₇, has been designed through dimensional reduction of the 3D prototype of Cs₂AgBiBr₆. Its unique quantum‐confined 2D bilayered motif results in the natural anisotropy of physical attributes, which accounts for its polarization‐sensitive response with large dichroic ratios.

Abstract

By dimensional reduction of the 3D motif of Cs₂AgBiBr₆, a lead‐free 2D hybrid double perovskite, (i‐PA)₂CsAgBiBr₇ (1, i‐PA=isopentylammonium), was successfully designed. It adopts a quantum‐confined bilayered structure with alternating organic and inorganic sheets. Strikingly, the unique 2D architecture endows it highly anisotropic nature of physical properties, including electric conductivity and optical absorption (the ratio α _b/α _c=1.9 at 405 nm). Such anisotropy attributes result in the strong polarization‐sensitive responses with large dichroic ratios up to 1.35, being comparable to some 2D inorganic materials. This is the first study on the hybrid double perovskites with strong polarization sensitivity. A crystal device of 1 also exhibits rapid response speed (ca. 200 μs) and excellent stabilities. The family of 2D hybrid double perovskites are promising optoelectronic candidates, and this work paves a new pathway for exploring new green polarization‐sensitive materials.

A new passivator, 4‐tert‐butylbenzylammonium iodide (tBBAI), is introduced, which accelerates charge extraction while retarding nonradiative recombination, boosting the power conversion efficiency of perovskite solar cells (PSCs) from 20% to 23.5% and reducing the hysteresis to barely detectable levels. tBBAI‐passivated PSCs also show excellent stability, retaining over 95% of their initial PCE after 500 h full‐sun illumination under maximum‐power‐point tracking.

Abstract

Passivation of interfacial defects serves as an effective means to realize highly efficient and stable perovskite solar cells (PSCs). However, most molecular modulators currently used to mitigate such defects form poorly conductive aggregates at the perovskite interface with the charge collection layer, impeding the extraction of photogenerated charge carriers. Here, a judiciously engineered passivator, 4‐tert‐butyl‐benzylammonium iodide (tBBAI), is introduced, whose bulky tert‐butyl groups prevent the unwanted aggregation by steric repulsion. It is found that simple surface treatment with tBBAI significantly accelerates the charge extraction from the perovskite into the spiro‐OMeTAD hole‐transporter, while retarding the nonradiative charge carrier recombination. This boosts the power conversion efficiency (PCE) of the PSC from ≈20% to 23.5% reducing the hysteresis to barely detectable levels. Importantly, the tBBAI treatment raises the fill factor from 0.75 to the very high value of 0.82, which concurs with a decrease in the ideality factor from 1.72 to 1.34, confirming the suppression of radiation‐less carrier recombination. The tert‐butyl group also provides a hydrophobic umbrella protecting the perovskite film from attack by ambient moisture. As a result, the PSCs show excellent operational stability retaining over 95% of their initial PCE after 500 h full‐sun illumination under maximum‐power‐point tracking under continuous simulated solar irradiation.

Publication date: 15 April 2020

Source: Joule, Volume 4, Issue 4

Author(s): Enrico Lamanna, Fabio Matteocci, Emanuele Calabrò, Luca Serenelli, Enrico Salza, Luca Martini, Francesca Menchini, Massimo Izzi, Antonio Agresti, Sara Pescetelli, Sebastiano Bellani, Antonio Esaú Del Río Castillo, Francesco Bonaccorso, Mario Tucci, Aldo Di Carlo

Publication date: May 2020

Source: Nano Energy, Volume 71

Author(s): Meng Zhang, Xun Cui, Yufen Wang, Bing Wang, Meidan Ye, Wenlong Wang, Chunyuan Ma, Zhiqun Lin

Addition of the n‐type dopant benzyl viologen (BV) into several best‐in‐class organic bulk‐heterojunctions (BHJ) is shown to consistently improve the power conversion efficiency (PCE) of the resulting solar cells. The presence of BV inside the BHJs increases the absorption coefficient, balances charge transport, and enhances the charge‐carrier density. These synergistic effects result in organic photovoltaics with a maximum PCE of 17.1%.

Abstract

Molecular doping is often used in organic semiconductors to tune their (opto)electronic properties. Despite its versatility, however, its application in organic photovoltaics (OPVs) remains limited and restricted to p‐type dopants. In an effort to control the charge transport within the bulk‐heterojunction (BHJ) of OPVs, the n‐type dopant benzyl viologen (BV) is incorporated in a BHJ composed of the donor polymer PM6 and the small‐molecule acceptor IT‐4F. The power conversion efficiency (PCE) of the cells is found to increase from 13.2% to 14.4% upon addition of 0.004 wt% BV. Analysis of the photoactive materials and devices reveals that BV acts simultaneously as n‐type dopant and microstructure modifier for the BHJ. Under optimal BV concentrations, these synergistic effects result in balanced hole and electron mobilities, higher absorption coefficients and increased charge‐carrier density within the BHJ, while significantly extending the cells' shelf‐lifetime. The n‐type doping strategy is applied to five additional BHJ systems, for which similarly remarkable performance improvements are obtained. OPVs of particular interest are based on the ternary PM6:Y6:PC₇₁BM:BV(0.004 wt%) blend for which a maximum PCE of 17.1%, is obtained. The effectiveness of the n‐doping strategy highlights electron transport in NFA‐based OPVs as being a key issue.

Strong Faraday rotation is demonstrated for methylammonium lead bromide (MAPbBr₃) single crystals. Coupled with low defect density, they are poised to represent a solution‐processed alternative for Faraday rotator applications, such as optical isolators and optical switches. Additionally, their Faraday rotation fits well with classical theory, allowing prediction of other perovskites for this application.

Abstract

Lead halide perovskites (LHPs) have become a promising alternative for a wide range of optoelectronic devices, thanks to their solution‐processability and impressive optical and electrical properties. More recently, LHPs have been investigated in magneto‐optic studies and have exhibited spin‐polarized emission, photoinduced magnetization, and long spin lifetimes. Here, the viability of methylammonium lead bromide (MAPbBr₃) single crystals as solution‐processed Faraday rotators is demonstrated. Compared to terbium gallium garnet, the industry standard in the visible, it is found that MAPbBr₃ exhibits Verdet constants (i.e., strength of Faraday effect) of similar or greater magnitude (up to 2.5x higher), with lower temperature dependence. Due to its low trap absorption, it is calculated that an optical isolator made from MAPbBr₃, with appropriate antireflection coatings, should reach ≈95% transmission and achieve 40 dB isolation for incoming powers of over 2 W. It is also shown that the Verdet constant of MAPbBr₃ can be calculated accurately from its dispersion in refractive index, allowing the possibility to predict similar effects in other perovskite materials.

All held together: A simple post‐treatment procedure uses 2‐aminoterephthalic acid as a cross‐linking agent to modify the exposed grain boundary of perovskite film, which is directly observed with conductive atomic force microscopy (C‐AFM). Under the optimized cross‐linking agent concentration, a solar cell achieves a power conversion efficiency (PCE) of 21.09 % and improved stability.

Abstract

Metal halide perovskite solar cells (PSCs), with their exceptional properties, show promise as photoelectric converters. However, defects in the perovskite layer, particularly at the grain boundaries (GBs), seriously restrict the performance and stability of PSCs. Now, a simple post‐treatment procedure involves applying 2‐aminoterephthalic acid to the perovskite to produce efficient and stable PSCs. By optimizing the post‐treatment conditions, we created a device that achieved a remarkable power conversion efficiency (PCE) of 21.09 % and demonstrated improved stability. This improvement was attributed to the fact that the 2‐aminoterephthalic acid acted as a cross‐linking agent that inhibited the migration of ions and passivated the trap states at GBs. These findings provide a potential strategy for designing efficient and stable PSCs regarding the aspects of defect passivation and crystal growth.

A conjugated polyelectrolyte is used for simultaneously tailoring the perovskite adjacent interfaces. Herein, for the first time, poly[(9,9‐bis(3′‐((N,N ‐dimethyl)‐N ‐ethyl‐ammonium)‐propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)]di‐iodide (PFN‐I)is exploited in inverted planar perovskite solar cells. At the hole transport layer/perovskite interface, the PFN‐I is beneficial for solving the dewetting issue. At the perovskite/electron transport layer interface, the PFN‐I is advantageous for passivating defects.

Interface engineering is an effective means to enhance the performance of thin‐film devices, such as perovskite solar cells (PSCs). Herein, a conjugated polyelectrolyte, poly[(9,9‐bis(3′‐((N,N ‐dimethyl)‐N ‐ethyl‐ammonium)‐propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)]di‐iodide (PFN‐I), is used at the interfaces between the hole transport layer (HTL)/perovskite and perovskite/electron transport layer simultaneously, to enhance the device power conversion efficiency (PCE) and stability. The fabricated PSCs with an inverted planar heterojunction structure show improved open‐circuit voltage (V _oc), short‐circuit current density (J _sc), and fill factor, resulting in PCEs up to 20.56%. The devices maintain over 80% of their initial PCEs after 800 h of exposure to a relative humidity 35–55% at room temperature. All of these improvements are attributed to the functional PFN‐I layers as they provide favorable interface contact and defect reduction.

A robust and fully functional solution‐processed interconnecting layer (ICL) is engineered to chemically and mechanically protect the underlying photoactive layer against interface protonation and penetration of the high boiling point solvent without further thermal treatment. Organic tandem solar cells with various photoactive layers exhibit high reliability and good reproducibility, demonstrating the superiority of the crosslinked ICL.

Abstract

The performance of tandem organic solar cells (OSCs) is directly related to the functionality and reliability of the interconnecting layer (ICL). However, it is a challenge to develop a fully functional ICL for reliable and reproducible fabrication of solution‐processed tandem OSCs with minimized optical and electrical losses, in particular for being compatible with various state‐of‐the‐art photoactive materials. Although various ICLs have been developed to realize tandem OSCs with impressively high performance, their reliability, reproducibility, and generic applicability are rarely analyzed and reported so far, which restricts the progress and widespread adoption of tandem OSCs. In this work, a robust and fully functional ICL is developed by incorporating a hydrolyzed silane crosslinker, (3‐glycidyloxypropyl)trimethoxysilane (GOPS), into poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and its functionality for reliable and reproducible fabrication of tandem OSCs based on various photoactive materials is validated. The cross‐linked ICL can successfully protect the bottom active layer against penetration of high boiling point solvents during device fabrication, which widely broadens the solvent selection for processing photoactive materials with high quality and reliability, providing a great opportunity to continuously develop the tandem OSCs towards future large‐scale production and commercialization.

There has been rapid progress in halide perovskite device performance but further improvements require a firm understanding of charge carrier photophysics. This article details the recent uses of time‐resolved optical microscopy techniques to understand nanoscale charge carrier transport and recombination mechanisms. Ongoing technical developments and future strategies to fill gaps in understanding of carrier behavior in perovskites are discussed.

Abstract

Halide perovskites have remarkable properties for relatively crudely processed semiconductors, including large optical absorption coefficients and long charge carrier lifetimes. Thanks to such properties, these materials are now competing with established technologies for use in cost‐effective and efficient light‐harvesting and light‐emitting devices. Nevertheless, the fundamental understanding of the behavior of charge carriers in these materials—particularly on the nano‐ to microscale—has, on the whole, lagged behind empirical device performance. Such understanding is essential to control charge carriers, exploit new device structures, and push devices to their performance limits. Among other tools, optical microscopy and spectroscopic techniques have revealed rich information about charge carrier recombination and transport on important length scales. In this progress report, the contribution of time‐resolved optical microscopy techniques to the collective understanding of the photophysics of these materials is detailed. The ongoing technical developments in the field that are overcoming traditional experimental limitations in order to visualize transport properties over multiple time and length scales are discussed. Finally, strategies are proposed to combine optical microscopy with complementary techniques in order to obtain a holistic picture of local carrier photophysics in state‐of‐the‐art perovskite devices.

This work aims to report a critical overview of recent progress in exciton physics of metal‐halide perovskites. These semiconductors are the subject of very intense study thanks to the unprecedented success in energy harvesting and light emitting applications. Interestingly the development of perovskite based devices has significantly outpaced understanding of their fundamental properties. One of the biggest puzzles of perovskites is related to exciton binding energy and its fine structure which are crucial for optoelectronic applications.

Abstract

The unprecedented increase of the power conversion efficiency of metal‐halide perovskite solar cells has significantly outpaced the understanding of their fundamental properties. One of the biggest puzzles of perovskites has been the exciton binding energy, which has proved to be difficult to determine experimentally. Many contradictory reports can be found in the literature with values of the exciton binding energy from a few meV to a few tens of meV. In this review the results of the last few years of intense investigation of the exciton physic in perovskite materials are summarized. In particular a critical overview of the different experimental approaches used to determine exciton binding energy is provided. The problem of exciton binding energy in the context of the polar nature of perovskite crystals and related polaron effects which have been neglected to date in most of work is discussed. It is shown that polaron effects can reconcile at least some of the experimental observations and controversy present in the literature. Finally, the current status of the exciton fine structure in perovskite materials is summarized. The peculiar carrier–phonon coupling can help to understand the intriguing efficiency of light emission from metal‐halide perovskites.

Colloidal core/shell quantum dots (QDs) exhibit promising optical and electrical properties. Herein, a comprehensive overview is presented of the recent developments in the engineering of the structure of core/shell QDs to tune exciton dynamics so as to improve the performance of QD‐sensitized solar cells.

Abstract

Semiconductor nanocrystals, the so‐called quantum dots (QDs), exhibit versatile optical and electrical properties. However, QDs possess high density of surface defects/traps due to the high surface‐to‐volume ratio, which act as nonradiative carrier recombination centers within the QDs, thereby deteriorating the overall solar cell performance. The surface passivation of QDs through the growth of an outer shell of different materials/compositions called “core/shell QDs” has proven to be an effective approach to reduce the surface defects and confinement potential, which can enable the broadening of the absorption spectrum, accelerate the carrier transfer, and reduce exciton recombination loss. Here, the recent research developments in the tailoring of the structure of core/shell QDs to tune exciton dynamics so as to improve solar cell performance are summarized. The role of band alignment of core and shell materials, core size, shell thickness/compositions, and interface engineering of core/thick shell called “giant” QDs on electron–hole spatial separation, carrier transport, and confinement potential, before and after grafting on the carrier scavengers (semiconductor/electrolyte), is described. Then, the solar cell performance based on core/shell QDs is introduced. Finally, an outlook for the rational design of core/shell QDs is provided, which can further promote the development of high‐efficiency and stable QD sensitized solar cells.

The thiazolium iodide‐passivated perovskite layer reduces CH₃NH₃ ⁺ thermal diffusion and shallow as well as deep traps, which in turn yield improved performance.

Abstract

Interface engineering has become one of the most facile and effective approaches to improve solar cells performance and its long‐term stability and to retard unwanted side reactions. Three passivating agents are developed which can functionalize the surface and induce hydrophobicity, by employing substituted thiazolium iodide (TMI) for perovskite solar cells fabrication. The role of TMI interfacial layers in microstructure and electro‐optical properties is assessed for structural as well as transient absorption measurements. TMI treatment resulted in V _OC and fill factor enhancement by reducing possible recombination paths at the perovskite/hole selective interface and by reducing the shallow as well as deep traps. These in turn allow to achieve higher performance as compared to the pristine surface. Additionally, the TMI passivated perovskite layer considerably reduces CH₃NH₃ ⁺ thermal diffusion and degradation induced by humidity. The un‐encapsulated perovskite solar cells employing TMI exhibit a remarkable stability under moisture levels (≈50% RH), retaining ≈95% of the initial photon current efficiency after 800 h of fabrication, paving the way towards a potential scalable endeavor.

Herein, how F, OH, and O mix terminations affect the work function of the Ti₃C₂/MAPbI₃ interface is studied, covering the whole phase‐space of mixtures and highlighting the mechanism of strong nonlinear behaviors. Using first‐principles calculations, the degree and origin of the work function non‐linearity is described and sized.

Abstract

MXenes are a recent family of 2D materials with very interesting electronic properties for device applications. One very appealing feature is the wide range of work functions shown by these materials, depending on their composition and surface terminations, that can be exploited to adjust band alignments between different material layers. In this work, based on density functional theory calculations, how mixed terminations of F, OH, and/or O affect the work function of Ti₃C₂ MXene is analyzed in detail, covering the whole phase‐space of mixtures. The Ti₃C₂/CH₃NH₃PbI₃ (MAPbI₃) perovskite coupled system for solar cell applications is also analyzed. A strong nonlinear behavior is found when varying the relative concentrations of OH, O, and F terminations, with the strongest effect of the OH groups in lowering the work function, already at a relative amount of 25%. A surprising minimum work function is found for relative OH:O fraction of 75:25, explained in terms of the nonlinear electronic response in screening the surface dipoles.

Stable perovskite thin films and solar cells are obtained by judicious incorporation of multifunctional tetrapropylammonium (TPA) cations in methylammonium iodide (MAPbI₃). Upon addition of TPA, a heterostructure is formed, which leads to the passivation of defects along with improved morphology. This study highlights a new strategy to enhance the stability of perovskite solar cells while maintaining high performance.

Abstract

Improving the performances of photovoltaic (PV) devices by suppressing nonradiative energy losses through surface defect passivation and enhancing the stability to the level of standard PV represents one critical challenge for perovskite solar cells. Here, reported are the advantages of introducing a tetrapropylammonium (TPA⁺) cation that combines two key functionalities, namely surface passivation of CH₃NH₃PbI₃ nanocrystals through strong ionic interaction with the surface and bulk passivation via formation of a type I heterostructure that acts as a recombination barrier. As a result, nonencapsulated perovskite devices with only 2 mol% of TPA⁺ achieve power conversion efficiencies over 18.5% with higher V _OC under air mass 1.5G conditions. The devices fabricated retain more than 85% of their initial performances for over 1500 h under ambient conditions (55% RH ± 5%). Furthermore, devices with TPA⁺ also exhibit excellent operational stability by retaining over 85% of the initial performance after 250 h at maximum power point under 1 sun illumination. The effect of incorporation of TPA⁺ on the structural and optoelectronic properties is studied by X‐ray diffraction, ultraviolet–visible absorption spectroscopy, ultraviolet photon–electron spectroscopy, time‐resolved photoluminescence, and scanning electron microscopy imaging. Atomic‐level passivation upon addition of TPA⁺ is elucidated employing 2D solid‐state NMR spectroscopy.

A simple low‐temperature‐processed In₂O₃/SnO₂ bilayer electron‐transport layer (ETL) is used for fabricating efficient perovskite solar cells (PSCs). The bilayer ETL with appropriate energy alignment is beneficial for charge transfer, thus minimizing open‐circuit voltage (V _OC) loss. An optimized planar PSC with a power conversion efficiency (PCE) of 23.24% is obtained. In contrast, devices based on single SnO₂ only achieve efficiency of 21.42%.

Abstract

An electron‐transport layer (ETL) with appropriate energy alignment and enhanced charge transfer is critical for perovskite solar cells (PSCs). However, interfacial energy level mismatch limits the electrical performance of PSCs, particularly the open‐circuit voltage (V _OC). Herein, a simple low‐temperature‐processed In₂O₃/SnO₂ bilayer ETL is developed and used for fabricating a new PSC device. The presence of In₂O₃ results in uniform, compact, and low‐trap‐density perovskite films. Moreover, the conduction band of In₂O₃ is shallower than that of Sn‐doped In₂O₃ (ITO), enhancing the charge transfer from perovskite to ETL, thus minimizing V _OC loss at the perovskite and ETL interface. A planar PSC with a power conversion efficiency of 23.24% (certified efficiency of 22.54%) is obtained. A high V _OC of 1.17 V is achieved with the potential loss at only 0.36 V. In contrast, devices based on single SnO₂ layers achieve 21.42% efficiency with a V _OC of 1.13 V. In addition, the new device maintains 97.5% initial efficiency after 80 d in N₂ without encapsulation and retains 91% of its initial efficiency after 180 h under 1 sun continuous illumination. The results demonstrate and pave the way for the development of efficient photovoltaic devices.

Recent progress of tin and mixed Pb–Sn halide perovskite solar cells is summarized, including an introduction of device structures, fabrication methods, strategies to improve both performance and stability, and an outlook of pure tin‐based halide, mixed Pb–Sn halide, and monolithic all‐perovskite tandem solar cells.

Abstract

Metal halide perovskites have recently attracted enormous attention for photovoltaic applications due to their superior optical and electrical properties. Lead (Pb) halide perovskites stand out among this material series, with a power conversion efficiency (PCE) over 25%. According to the Shockley–Queisser (SQ) limit, lead halide perovskites typically exhibit bandgaps that are not within the optimal range for single‐junction solar cells. Partial or complete replacement of lead with tin (Sn) is gaining increasing research interest, due to the promise of further narrowing the bandgaps. This enables ideal solar utilization for single‐junction solar cells as well as the construction of all‐perovskite tandem solar cells. In addition, the usage of Sn provides a path to the fabrication of lead‐free or Pb‐reduced perovskite solar cells (PSCs). Recent progress in addressing the challenges of fabricating efficient Sn halide and mixed lead–tin (Pb–Sn) halide PSCs is summarized herein. Mixed Pb–Sn halide perovskites hold promise not only for higher efficiency and more stable single‐junction solar cells but also for efficient all‐perovskite monolithic tandem solar cells.

Addition of the n‐type dopant benzyl viologen (BV) into several best‐in‐class organic bulk‐heterojunctions (BHJ) is shown to consistently improve the power conversion efficiency (PCE) of the resulting solar cells. The presence of BV inside the BHJs increases the absorption coefficient, balances charge transport, and enhances the charge‐carrier density. These synergistic effects result in organic photovoltaics with a maximum PCE of 17.1%.

Abstract

Molecular doping is often used in organic semiconductors to tune their (opto)electronic properties. Despite its versatility, however, its application in organic photovoltaics (OPVs) remains limited and restricted to p‐type dopants. In an effort to control the charge transport within the bulk‐heterojunction (BHJ) of OPVs, the n‐type dopant benzyl viologen (BV) is incorporated in a BHJ composed of the donor polymer PM6 and the small‐molecule acceptor IT‐4F. The power conversion efficiency (PCE) of the cells is found to increase from 13.2% to 14.4% upon addition of 0.004 wt% BV. Analysis of the photoactive materials and devices reveals that BV acts simultaneously as n‐type dopant and microstructure modifier for the BHJ. Under optimal BV concentrations, these synergistic effects result in balanced hole and electron mobilities, higher absorption coefficients and increased charge‐carrier density within the BHJ, while significantly extending the cells' shelf‐lifetime. The n‐type doping strategy is applied to five additional BHJ systems, for which similarly remarkable performance improvements are obtained. OPVs of particular interest are based on the ternary PM6:Y6:PC₇₁BM:BV(0.004 wt%) blend for which a maximum PCE of 17.1%, is obtained. The effectiveness of the n‐doping strategy highlights electron transport in NFA‐based OPVs as being a key issue.

There has been rapid progress in halide perovskite device performance but further improvements require a firm understanding of charge carrier photophysics. This article details the recent uses of time‐resolved optical microscopy techniques to understand nanoscale charge carrier transport and recombination mechanisms. Ongoing technical developments and future strategies to fill gaps in understanding of carrier behavior in perovskites are discussed.

Abstract

Halide perovskites have remarkable properties for relatively crudely processed semiconductors, including large optical absorption coefficients and long charge carrier lifetimes. Thanks to such properties, these materials are now competing with established technologies for use in cost‐effective and efficient light‐harvesting and light‐emitting devices. Nevertheless, the fundamental understanding of the behavior of charge carriers in these materials—particularly on the nano‐ to microscale—has, on the whole, lagged behind empirical device performance. Such understanding is essential to control charge carriers, exploit new device structures, and push devices to their performance limits. Among other tools, optical microscopy and spectroscopic techniques have revealed rich information about charge carrier recombination and transport on important length scales. In this progress report, the contribution of time‐resolved optical microscopy techniques to the collective understanding of the photophysics of these materials is detailed. The ongoing technical developments in the field that are overcoming traditional experimental limitations in order to visualize transport properties over multiple time and length scales are discussed. Finally, strategies are proposed to combine optical microscopy with complementary techniques in order to obtain a holistic picture of local carrier photophysics in state‐of‐the‐art perovskite devices.

In article number https://doi.org/10.1002/adfm.2019083431908343, Yumin Liu, Xing‐Zhong Zhao, and co‐workers develop a δ‐CsPbI₃ intermediate phase growth (IPG) strategy for achieving high and controllable Cs⁺ incorporation and fabricating large‐grain perovskite thin films. The δ‐CsPbI₃ phase in the PbI₂ film, which serves as the cesium source, facilitates the growth of perovskite grains. This CsPbI₃‐IPG is a facile and effective strategy to produce large‐grain Cs⁺ incorporated perovskite films via sequential deposition.