Ligang Yuan

Spatial heterogeneity in the functional optical properties of CH₃NH₃PbI₃ thin films is mapped on the microscopic scale using femtosecond pump‐probe transient absorption and time‐resolved photoluminescence microscopy. The coregistration of short‐ (sub‐picosecond) and long‐time (nanosecond) contrast provides information about the origin of the heterogeneity. Furthermore, the variation of functional properties is found to be only partially correlated with physical structure.

Abstract

The spatial heterogeneity of carrier dynamics in polycrystalline metal halide perovskite (MHP) thin films has a strong influence on photovoltaic device performance; however, the underlying cause is not yet clearly understood. Here, the sub‐micrometer scale mapping of charge carrier dynamics in CH₃NH₃PbI₃ thin films using time‐resolved nonlinear optical microscopy, specifically transient absorption microscopy (TAM) with sub‐picosecond (ps) and time‐resolved photoluminescence (PL) microscopy with nanosecond temporal resolution is reported. To study the influence of physical morphology on charge carrier dynamics, MHP thin films having granular‐ and fibrous structures are investigated. On both types of films, spatial regions with short‐lived transient gain signals (fast nonradiative relaxation within ≈1 ps) typically show slower charge recombination via radiative relaxation, which is attributed to the presence of additional energy states near the band edge. In addition, fibrous films show longer PL lifetimes. Interestingly, the functional contrast shown in TAM images exhibits fundamental differences from the structural contrast shown in scanning electron microscopy images, implying that the variation of trap density in the bulk contributes to the observed spatial heterogeneity in carrier dynamics.

Anomalous experimental evidences of 2D perovskites from different aspects are presented, which deviate from the general carrier dynamics with irreversible trapping but agree well with the energy reservoir model. A transient energy reservoir mechanism outcompeting nonradiative loss is established in the 2D perovskites, providing a new clue to understand the lauded defect tolerance of perovskites.

Abstract

2D Ruddlesden−Popper type perovskites have attracted enormous attention due to their natural multiquantum‐well structure. However, there is still mystery regarding the behavior of photocarriers, especially the exciton fine structure behind the excellent optoelectronic performance. The coexistence of two strikingly different decay components in time‐resolved photoluminescence is inconsistent with the high internal quantum yield (QY_IN = ≈0.7) in the conventional model for radiative and nonradiative recombinations (QY_IN = τ_nr/(τ_nr + τ_r) = 17%). Here it is revealed that there is a special transient energy reservoir outcompeting nonradiative loss in 2D Ruddlesden−Popper type perovskites. Upon optical excitation, the bright excitons rapidly relax into the low‐lying energy reservoir before nonradiative recombination occurs. Interestingly, the energy in the reservoir is not lost. The carriers in this energy reservoir can spontaneously transfer back to the bright states and can still effectively contribute to the photovoltaic and photonic properties of the perovskites. This investigation provides a novel insight into the mechanism for the lauded defect tolerance of 2D perovskites by highly efficient energy storage via a transient reservoir.

CH₃NH₃PbI₃ exhibits a superior piezophotocatalytic hydrogen generation rate upon concurrent light and mechanical stimulations, much higher than that of piezocatalytic and photocatalytic hydrogen evolution rate as well as their sum. Combining piezocatalysis and photocatalysis of semiconductor photocatalysts to attain a collective piezophotocatalysis may represent an appealing strategy for efficient solar energy conversion, including water splitting, organic fuel production, etc.

Abstract

To alleviate photoinduced charge recombination in semiconducting nanomaterials represents an important endeavor toward high‐efficiency photocatalysis. Here a judicious integration of piezoelectric and photocatalytic properties of organolead halide perovskite CH₃NH₃PbI₃ (MAPbI₃) to enable a piezophotocatalytic activity under simultaneous ultrasonication and visible light illumination for markedly enhanced photocatalytic hydrogen generation of MAPbI₃ is reported. The conduction band minimum of MAPbI₃ is higher than hydrogen generation potential (0.046 V vs normal hydrogen electrode), thereby rendering efficient hydrogen evolution. In addition, the noncentrosymmetric crystal structure of MAPbI₃ enables its piezoelectric properties. Thus, MAPbI₃ readily responds to external mechanical force, creating a built‐in electric field for collective piezophotocatalysis as a result of effective separation of photogenerated charge carriers. The experimental results show that MAPbI₃ powders exhibit superior piezophotocatalytic hydrogen generation rate (23.30 µmol h⁻¹) in hydroiodic acid (HI) solution upon concurrent light and mechanical stimulations, much higher than that of piezocatalytic (i.e., 2.21 µmol h⁻¹) and photocatalytic (i.e., 3.42 µmol h⁻¹) hydrogen evolution rate as well as their sum (i.e., 5.63 µmol h⁻¹). The piezophotocatalytic strategy provides a new way to control the recombination of photoinduced charge carriers by cooperatively capitalizing on piezocatalysis and photocatalysis of organolead halide perovskites to yield highly efficient piezophotocatalysis.

The interface and bulk defects of perovskite solar cells are distinguished and quantified, and are for the first time traced in situ using an expanded admittance model. A fullerene derivative [6, 6]‐phenyl‐C61‐butyric acid (PCBA) is introduced into the TiO₂/perovskite interface to release the interface stress.

Abstract

The stability issue that is obstructing commercialization of the perovskite solar cell is widely recognized, and tremendous effort has been dedicated to solving this issue. However, beyond the apparent thermal and moisture stability, more intrinsic semiconductor mechanisms regarding defect behavior have yet to be explored and understood. Herein, defects are quantified; especially interface defects, within the cell to reveal their impact on device performance and especially stability. Both the bulk and interface defects are distinguished and traced in situ using an expanded admittance model when the cell degrades in its efficiency under illumination or voltage. The electric field‐induced interface, rather than bulk defects, is found to have a direct correlation to stability. Releasing the interface strain using a fullerene derivative is an effective way to suppress interface defect formation and improve stability. Overall, this work provides a quantitative approach to probing the semiconductor mechanism behind the stability issue, and the inherent correlation discovered here among the electric field, interface strain, interface defects, and cell stability has important implications for ongoing device stability engineering.

Nature Photonics, Published online: 19 August 2019; doi:10.1038/s41566-019-0505-4

The photochemistry of halide‐related defects affects the optoelectronic properties of lead–halide perovskite semiconductors and their reactivity to external stimuli such as light and environmental molecules.

Abstract

The presence of various types of chemical interactions in metal‐halide perovskite semiconductors gives them a characteristic “soft” fluctuating structure, prone to a wide set of defects. Understanding of the nature of defects and their photochemistry is summarized, which leverages the cooperative action of density functional theory investigations and accurate experimental design. This knowledge is used to describe how defect activity determines the macroscopic properties of the material and related devices. Finally, a discussion of the open questions provides a path towards achieving an educated prediction of device operation, necessary to engineer reliable devices.

A general approach for lab‐to‐manufacturing translation is developed to achieve high‐performance flexible organic solar modules without obvious efficiency loss. The shear impulse during the coating/printing process is applied to control the morphology evolution of the bulk heterojunction layer for both fullerene and nonfullerene acceptor systems. A quantitative transformation factor of shear impulse between slot‐die printing and spin‐coating is detected.

Abstract

The blossoming of organic solar cells (OSCs) has triggered enormous commercial applications, due to their high‐efficiency, light weight, and flexibility. However, the lab‐to‐manufacturing translation of the praisable performance from lab‐scale devices to industrial‐scale modules is still the Achilles' heel of OSCs. In fact, it is urgent to explore the mechanism of morphological evolution in the bulk heterojunction (BHJ) with different coating/printing methods. Here, a general approach to upscale flexible organic photovoltaics to module scale without obvious efficiency loss is demonstrated. The shear impulse during the coating/printing process is first applied to control the morphology evolution of the BHJ layer for both fullerene and nonfullerene acceptor systems. A quantitative transformation factor of shear impulse between slot‐die printing and spin‐coating is detected. Compelling results of morphological evolution, molecular stacking, and coarse‐grained molecular simulation verify the validity of the impulse translation. Accordingly, the efficiency of flexible devices via slot‐die printing achieves 9.10% for PTB7‐Th:PC₇₁BM and 9.77% for PBDB‐T:ITIC based on 1.04 cm² . Furthermore, 15 cm² flexible modules with effective efficiency up to 7.58% (PTB7‐Th:PC₇₁BM) and 8.90% (PBDB‐T:ITIC) are demonstrated with satisfying mechanical flexibility and operating stability. More importantly, this work outlines the shear impulse translation for organic printing electronics.

Representative research studies on free carrier, exciton, and phonon dynamics in lead‐halide perovskites, performed with terahertz (THz) time‐domain spectroscopy (THz‐TDS) and time‐resolved THz spectroscopy (TRTS), are reviewed. The power of THz techniques to elucidate the photophysics, and hence the outstanding photovoltaic performance of the halide perovskite materials, is illustrated.

Abstract

Terahertz time‐domain spectroscopy is a noncontact, coherent technique that can probe dynamics of carriers, phonons and excitons, and the interplay among these degrees of freedom, which determines the functionalities of the system. In the past few years, lead‐halide perovskites have shown to be a promising class of materials in the areas of solar cells, light emitting diodes, lasers, photodetectors, and field‐effect transistors. In these electronic and photonic devices, the knowledge of the dynamics of charge carriers and other low‐energy excitations is crucial to understand the underlying physics that ultimately determines the device performances. Here, some of the most representative works in the area of halide perovskite research using terahertz time‐domain spectroscopy and time‐resolved terahertz spectroscopy are reviewed, highlighting the power of ultrafast terahertz techniques on this class of material system.

A maximum external quantum efficiency of in situ fabricated CsPbBr₃ Nanoparticles (NPs) light‐emitting diode is demonstrated to be 17.4% by introducing sodium bromide to CsPbBr₃ NPs to passivate defect and promote the charge transfer ability.

Abstract

All‐inorganic perovskite has attracted much attention because of the higher stability. Many organic additives such as alkyl chain ammonium and polymers are usually introduced into perovskite to improve their performance. However, the long chain ammonium cations in perovskite may restrain the carrier transfer ability and ultimately deteriorate the performance of light‐emitting diodes (LEDs). In this work, the CsPbBr₃ nanoparticles (NPs) are in situ fabricated by the synergistic effect of poly(ethylene oxide) and phenethylammonium bromide (PEABr). Particularly, sodium bromide (NaBr) with better conductivity is successfully introduced into CsPbBr₃ NPs to substitute PEA partially, ultimately to passivate the defect and promote the carrier transfer ability. Besides, the addition of NaBr results in a better promotion for electron mobility than for hole mobility leading to a more balanced charge transport in devices. It enables NaBr based CsPbBr₃ NPs green LEDs to exhibit a maximum external quantum efficiency (EQE_max) of 17.4%, which presents obvious enhancement compared to the LEDs without NaBr (EQE_max = 12%). Further, NaBr based CsPbBr₃ NPs LEDs with a large area of 108 mm² still show a high maximum EQE of 10.2%. Above all, this work provides a feasible way of adding metal additive in perovskite films to improve the performance of perovskite LEDs.

Calculations of Shockley–Queisser limits for perovskite solar cells under artificial light sources reveal the existence of an unusual zone, in which the bandgaps (E _g) of commonly used perovskite materials are too small to harvest photonic energy efficiently. Accordingly, increasing the value of E _g of the perovskite solar cell, by incorporating Br⁻ ions, improves the power conversion efficiencies under indoor lighting conditions.

Abstract

Indoor photovoltaics (IPVs) are attracting renewed interest because they can provide sustainable energy through the recycling of photon energy from household lighting facilities. Herein, the Shockley–Queisser model is used to calculate the upper limits of the power conversion efficiencies (PCEs) of perovskite solar cells (PeSCs) for two types of artificial light sources: fluorescent tubes (FTs) and white light–emitting diodes (WLEDs). An unusual zone is found in which the dependence of the PCEs on the bandgap (E _g) under illumination from the indoor lighting sources follows trends different from that under solar irradiation. In other words, IPVs exhibiting high performance under solar irradiation may not perform well under indoor lighting conditions. Furthermore, the ideal bandgap energy for harvesting photonic power from these indoor lighting sources is ≈1.9 eV—a value higher than that of common perovskite materials (e.g., for CH₃NH₃PbI₃). Accordingly, Br⁻ ions are added into the perovskite films to increase their values of E _g. A resulting PeSC featuring a wider bandgap exhibits PCEs of 25.94% and 25.12% under illumination from an FT and a WLED, respectively. Additionally, large‐area (4 cm²) devices are prepared for which the PCE reaches ≈18% under indoor lighting conditions.

Herein, a simple cation exchange growth (CEG) method is demonstrated that replaces the organic MA⁺ cation with Cs⁺ to produce a high‐quality black γ‐phase CsPbI₃ perovskite device, enhancing both power conversion efficiency and stability. As a result, the device fabricated using the optimized CEG method yields efficiency up to 14.1%.

Abstract

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.

Giant electric bias‐induced tunability of photoluminescence and photoresistance in hybrid perovskite films on ferroelectric substrates is achieved in CH₃NH₃PbI₃/Pb(Mg_1/3Nb_2/3)_0.7Ti_0.3O₃ structure. The thicker (thinner) perovskite film is affected by the converse piezoelectric (the electrostatic effect) of piezoelectric platforms. This work paves the way toward solution‐processable optoelectronics with high electric‐bias tunability.

Abstract

Hybrid organic–inorganic perovskites represent the frontier of optoelectronic research due to their outstanding physical properties and remarkable photovoltaic performance. Despite the success of perovskite‐based photovoltaic devices, the investigation on tuning photoelectric properties of perovskites is still scarce. Here, giant modulations of photoluminescence (up to 91.3%) and photoresistance (up to 70.8%) are achieved in CH₃NH₃PbI₃ films by applying an electric bias on single‐crystal ferroelectric Pb(Mg_1/3Nb_2/3)_0.7Ti_0.3O₃ substrates. The results indicate that the electrostatic (converse piezoelectric) effect is predominant in thinner (thicker) film, resulting in rich optical and electronic tuning phenomena. This work integrates hybrid perovskites with piezoelectric platforms, paving the way toward solution‐processed piezophototronic and bias‐tunable optoelectronics.

Publication date: 16 October 2019

Source: Joule, Volume 3, Issue 10

Author(s): Yuanyuan Fan, Junjie Fang, Xiaoming Chang, Ming-Chun Tang, Dounya Barrit, Zhuo Xu, Zhiwu Jiang, Jialun Wen, Huan Zhao, Tianqi Niu, Detlef-M. Smilgies, Shengye Jin, Zhike Liu, Er Qiang Li, Aram Amassian, Shengzhong (Frank) Liu, Kui Zhao

Context & Scale

Summary

Graphical Abstract

Perovskite solar cells (PVSCs) with discrete SnO₂ nanoparticle modification layers are constructed via spin coating the SnO₂ dispersions on poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The discrete SnO₂ nanoparticle film let holes pass and block electrons to diffuse toward PEDOT:PSS, which enhances the extraction efficiency, leading to an increase in a power conversion efficiency of p‐i‐n‐type PVSCs.

Poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is the most widely used hole transport materials for perovskite solar cells (PVSCs) with a p‐i‐n structure. However, the solar cells based on PEDOT:PSS show a low photoconversion efficiency due to the poor crystallinity of a perovskite film on it. Besides, the acidity of PEDOT:PSS performance critically influences the long‐term stability of PVSCs. Herein, a layer of the discrete SnO₂ nanoparticle film is deposited on the surface of PEDOT:PSS to modify the surface of the PEDOT:PSS film. This discrete SnO₂ nanoparticle film acts as the buffer layer between the PEDOT:PSS and MAPbI₃, which not only improves the crystallization of the quality of the perovskite film, but also provides a selective‐carrier pathway to enhance the extraction of holes and to block the diffusion of electrons. The SnO₂ modified devices show a power conversion efficiency of 18.04%, with a great improvement compared with the 12.24% efficiency of PEDOT:PSS only devices. This work demonstrates that it is possible to enhance the performance of PVSCs via n‐type nanoparticle modification of hole transport layer and provides a new guidance for PVSCs interface modification engineering.

A bifunctional dye molecule, 5,15‐bis(2,6‐dioctoxyphenyl)‐10‐(bis(4‐hexylphenyl)‐amino‐20‐4‐carboxyphenylethynyl)porphyrinato]zinc(II) (YD₂‐o‐C8), is introduced into CsPbI₂Br PSCs. It not only broadens the light absorption range of the perovskite but also reduces the energy loss (E _loss) by interface passivation. As a result, the efficiency markedly enhances from 7.02% to 10.13%, featuring a short‐circuit current (J _SC) of 12.05 mA cm⁻² and a record‐high open‐circuit voltage (V _OC) of 1.37 V.

Inorganic lead halide perovskites are attracting increasing attention due to their much better thermal stability than the organic–inorganic hybrid perovskite materials. Thus, the low power conversion efficiency (PCE) is a key issue for the inorganic lead halide perovskite solar cells (PSCs). This is mainly due to their wider bandgap and larger energy loss (E _loss) in the devices. Herein, for solving this issue, a dye molecule‐assisted engineering using the dye of 5,15‐bis(2,6‐dioctoxyphenyl)‐10‐(bis(4‐hexylphenyl)‐amino‐20‐4‐carboxyphenylethynyl)porphyrinato]zinc(II) (YD₂‐o‐C8) is demonstrated. Results indicate that this molecule has a bifunctional effect, not only as a co‐sensitization layer for CsPbIBr₂ with broader absorption spectrum but also reduces the E _loss by interface passivation. Specifically, the light absorption range of the photoactive layer is broadened from 600 to nearly 680 nm. At the same time, the interfacial charge recombination is highly reduced. After optimizing, the champion PCE is enhanced from 7.02% to 10.13%, and record‐high open‐circuit voltage (V _OC) of 1.37 V and short‐circuit currents (J _SC) of 12.05 mA cm⁻² are achieved. This study opens a simple and efficient way to improve the efficiency of inorganic PSCs.

For developing low‐cost and high‐efficiency planar perovskite solar cells (PSCs), a straightforward low‐temperature chemical bath deposition process is developed to prepare a Co‐doped TiO₂ (Co‐TiO₂) electron transport layer (ETL); the optoelectrical properties of the TiO₂ ETL are significantly improved by Co‐doping. Finally, the efficiency of the PSCs is increased from 17.40% for TiO₂ to 19.10% for the Co‐TiO₂ ETL.

Planar hybrid perovskite solar cells (PSCs) attract great attention due to their obvious advantages of low‐temperature processing with a high power conversion efficiency (PCE) up to 23.32%. Here, Co‐doped TiO₂ (Co‐TiO₂) deposited by a straightforward low‐temperature chemical bath deposition (CBD) method is explored. Using Co‐TiO₂ as an electron transport layer (ETL) for the planar PSCs, the effects of doping on TiO₂ morphology, electronic properties, and solar cell performance are investigated. The PCE increases to 19.10% when the Co doping concentration is optimized at 5 mol%, an increase of 17.40% compared with that using the pristine TiO₂. Meanwhile, the notorious J–V hysteresis is suppressed to a greater extent. Considering that the low‐temperature CBD is comparable with continuous roll‐to‐roll processing, it makes the process and the Co‐TiO₂ ETL potential candidates for low‐cost commercialization.

Solution‐processable Ga₂O₃ nanocrystals are developed as a novel electron‐transporting layer for high‐performance perovskite solar cells. The smooth film of Ga₂O₃ nanocrystals offers a better interface with perovskite and improves charge transport efficiency. The Ga₂O₃‐based device shows negligible hysteresis unlike the TiO₂‐based analogue.

The electron‐transporting layer (ETL) plays a very important role in perovskite solar cells (PSCs). The traditional TiO₂ ETL exhibits drawbacks such as complex preparation process and low stability. Devices incorporating TiO₂ as the ETL also show large hysteresis that limits their performance. Herein, Ga₂O₃ nanocrystals (NCs), prepared by a solution process, are applied as an ETL in n‐i‐p planar structured PSCs. The Ga₂O₃‐based devices exhibit negligible hysteresis and achieve higher performance than the TiO₂‐based devices. Due to better energy level matching and smoother surface morphology, films of Ga₂O₃ NCs make good interfacial contact with the perovskite top layer, improving the charge transport efficiency. The perovskite layer also exhibits high crystallinity. Unlike TiO₂, which is commonly prepared by high‐temperature sintering or solution hydrolysis, films of Ga₂O₃ NCs can be prepared by solution spin‐coating at a low temperature. This greatly reduces the complexity of fabrication and improves device performance.

Two novel hole‐transporting materials (HTMs) based on 9‐(4‐methoxyphenyl) carbazole and benzodithiophene cores are synthesized. The impact of these cores on the physicochemical properties and performance of perovskite solar cells (PSCs) based on these HTMs are investigated. The newly developed N1,N1′‐(9‐(4‐methoxyphenyl)‐9H‐carbazole‐3,6‐diyl)bis(N1‐(4‐(bis(4‐methoxyphenyl)amino)phenyl)‐N4,N4‐bis(4‐methoxyphenyl)benzene‐1,4‐diamine) (PhCz‐4MeOTPA)‐based PSC exhibits a power conversion efficiency of 16.04% along with enhanced stability under heat and illumination.

Perovskite solar cells (PSCs) possess both high‐power conversion efficiency (PCE) and good operation stability for future application. Although many different types of hole‐transporting materials (HTMs) are assessed, few dopant‐free small organic molecule HTMs‐based PSC cells exist, which exhibit excellent stability under both heat and illumination. Herein, two novel HTMs that are based on 9‐(4‐methoxyphenyl) carbazole and benzodithiophene cores are synthesized and named N1,N1′‐(9‐(4‐methoxyphenyl)‐9H‐carbazole‐3,6‐diyl)bis(N1‐(4‐(bis(4‐methoxyphenyl)amino)phenyl)‐N4,N4‐bis(4‐methoxyphenyl)benzene‐1,4‐diamine) (PhCz‐4MeOTPA) and N1,N1′‐(benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl)bis(N1‐(4‐(bis(4‐methoxyphenyl)amino)phenyl)‐N4,N4‐bis(4‐methixyphenyl)benzene‐1,4‐diamine) (BDT‐4MeOTPA). Of the two HTMs, PhCz‐4MeOTPA possesses a lower level of planarity than that of BDT‐4MeOTPA, which inhibits molecular stacking to improve film quality and increases hole‐transport mobility and charge transport. A PCE of 16.04% is achieved with the application of dopant‐free PhCz‐4MeOTPA in PSCs, which is higher than that of dopant‐free BDT‐4MeOTPA. The unencapsulated PSC devices based on PhCz‐4MeOTPA maintain 82% of their initial values under continuous sun illumination in an ambient environment at 40–45 °C after 672 h and 92% of their initial values at 80 °C in an ambient environment after 1200 h in the dark.

Perovskite solar cells are modified by dropping alkylammonium solutions over CH₃NH₃PbI₃ films and lead to an increase in the stability after exposure to humidity. In the presence of the alkylammonium chains, the bulk perovskite is converted to a 2D/3D structure that helps the device to retain its performance for longer.

Hybrid organic and inorganic perovskite solar cells lack long‐term stability, and this negatively impacts the widespread application of this emerging and promising photovoltaic technology. Herein, aiming to increase the stability of perovskite films based on CH₃NH₃PbI₃ and to deeply understand the formation of 2D structures, solutions of alkylammonium chlorides containing 8, 10, and 12 carbons are introduced during the spin‐coating on the surface of 3D perovskite films leading to the in situ formation of 2D structures. It is possible to identify the chemical formulae of some 2D structures formed by X‐ray diffraction and UV–vis analysis of the modified films. Interestingly, the increase in the stability of the CH₃NH₃PbI₃ films due to the formation of a 2D + 3D perovskite network is only possible in planar TiO₂ substrates. The increase in stability of the CH₃NH₃PbI₃ films follows the surfactant molecule order: octylammonium (8C) > decylammonium (1 °C) > dodecylammonium (12C) chlorides > standard. An increase of 17.6% in the lifetime of the devices assembled with octylammonium‐modified perovskite film is observed compared with that of the standard device, which is directly linked to the improvement of the charge carrier lifetimes obtained from time‐correlated single photon counting measurements.

Surface‐modified NiO _x nanoparticles (NPs) as hole transport materials in n‐i‐p‐structured perovskite solar cells are studied. The modified NiO _x NPs disperse well in chlorobenzene, and their film forms smooth and pinhole‐free layers, which show good electrical conductivity and improved extraction properties. The power conversion efficiency is improved from 5.5% to 13.1%.

Modified NiO _x nanoparticles (NPs) developed via surface engineering are applied to a hole transport layer (HTL) in n‐i‐p‐structured perovskite solar cells (PSCs). Hexanoic acid (HA) as a surfactant improves the dispersibility of NiO _x NPs in chlorobenzene (CB). The conductivity of the NiO _x ‐HA film is 1.20×10−5S cm−1, which is superior to that of 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenyl‐amine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) with dopants. The NiO _x ‐HA film shows better hole extraction properties compared with the pristine NiO _x film. The NiO _x ‐HA NPs form closely packed and pinhole‐free films, leading to improved device performance with a power conversion efficiency from 5.5% to 13.1%.

Trihydrazine dihydriodide is successfully used as an additive for solution deposition of a formamidinium tin iodide (FASnI₃) perovskite layer, resulting in improved surface morphology and reduced carrier concentration. Using the derived FASnI₃ layer as a light absorber, a maximum power conversion efficiency of 8.48% is achieved in a planar‐heterojunction solar cell using common precursor SnI₂ with 99% purity.

The deposition of a uniform and dense tin‐based perovskite layer with low defect‐caused background carrier density is crucial for achieving efficient tin perovskite solar cells (PSCs). These defects are mainly caused by the rapid oxidation of Sn²⁺ to Sn⁴⁺ in tin perovskite during device fabrication. Herein, trihydrazine dihydriodide ((N₂H₄)₃(HI)₂) is used as an additive for solution deposition of a formamidinium tin iodide (FASnI₃) perovskite layer. The resultant FASnI₃ layer is homogeneous with full surface coverage; moreover, the content of Sn⁴⁺ is significantly reduced in the film from the SnI₂ precursor owing to the reductive property of (N₂H₄)₃(HI)₂. With the high‐quality FASnI₃ layer as a light absorber, planar‐heterojunction perovskite solar cells are fabricated, exhibiting a maximum power conversion efficiency of 8.48% and good reproducibility. This work opens new possibilities for achieving efficient lead‐free tin‐based perovskite solar cells.

Three novel polytriphenylamine‐based polymers (H‐Z1, H‐Z2, and H‐Z3) are designed and applied as hole‐transport layers in all‐inorganic perovskite solar cells. Due to the gradual deepening of the highest occupied molecular orbital energy levels from H‐Z1, H‐Z2 to H‐Z3, the energy loss (E _loss) can be decreased from 0.69, 0.64, to 0.62 eV for H‐Z1, H‐Z2, and H‐Z3, respectively.

The energy loss (E _loss) control via interfacial engineering is a significant indispensible methodology to realize high‐performance all‐inorganic perovskite solar cells (PVSCs). Herein, three novel polytriphenylamine‐based polymer derivatives (H‐Z1, H‐Z2, and H‐Z3) are synthesized, and the energy levels of these polymers are tuned feasibly through introducing the electron‐withdrawing group of trifluoromethyl in the triphenylamine (TPA) unit. These very deep HOMO energy levels are very beneficial for improving the open‐circuit voltages (V_ocs) in PVSCs with the potentially decreased E _losss. Due to the gradual deepening of HOMO energy levels from H‐Z1, H‐Z2 to H‐Z3, the V_ocs are elevated from 1.23, 1.28 to 1.30 V, respectively, where the E _loss s are decreased from 0.69, 0.64, to 0.62 eV for H‐Z1, H‐Z2, and H‐Z3, respectively. Interestingly, both of the H‐Z1‐ and H‐Z2‐based devices show the highest PCEs, over 14%, in all‐inorganic PVSCs, which are effectively comparable to the results of reference device using Spiro‐OMeTAD as HTL. Thus, through the efficient atomic engineering and chemical modification in corresponding p‐typed polymers, excellent hole transport polymers are achieved for high‐performance and stable PVSCs with very low E _loss.

Perovskite solar cell technology is in the advent of commercial entrance. These materials offer several new value propositions that can allow short‐term monetization in emerging applications, such as Internet‐of‐things or building‐integrated photovoltaics. Prospective offerings perovskite photovoltaics could deliver for high‐value markets, such as utility‐scale photovoltaics, and the feasibility of large deployments are also discussed.

Perovskite solar cell technology is fast approaching its first commercial deployment, with the 10‐year mark since the first research having passed recently. Commercial entrance seems very tangible, but there are a number of remaining challenges related to various economic and technical factors. Conventional photovoltaic markets, such as utility scale photovoltaics, are quite rigid and very demanding for a new entrant. Perovskites offer several new value propositions, which offer monetization prospects in the near future, if properly used. In particular, functionalities such as flexibility, high specific power, and good low‐light performance enable new applications and broadening of the conventional PV usage. The specific cases of internet of things and building‐integrated photovoltaics are discussed, and market opportunities are analyzed. Technology incubation with simultaneous market presence in emerging applications can provide essential economic stability and time for the technology to develop into its full potential. Opportunities in high‐value markets and massive‐scale deployment are also addressed, with the analysis of potentially disruptive offerings being promised by perovskite photovoltaic technology.

The initial stages of MAPbI₃ photodegradation prior to any significant change in light absorption are studied, with independent control of sample temperature and sunlight intensity (1–500 suns). Under the combined action of light and heat, a strong reduction of photoluminescence (PL) is observed. In contrast, illumination of perovskite films (with an intensity up to 500 suns) without heating induces considerable PL enhancement.

The initial stages of photo‐degradation of CH₃NH₃PbI₃ (MAPbI₃) thin films prior to any significant change in light absorption are studied in experiments with independent control of sample temperature and intensity of concentrated sunlight from 50 to 500 suns. Photo‐stability of the MAPbI₃ film is revealed to be extremely sensitive to the sample temperature. Under the combined action of light and heat (either by concentrated sunlight or by external heating), a strong reduction of the film photoluminescence (PL) without changes in the perovskite light absorption can be observed during the initial stages of degradation. In contrast, illumination of perovskite films (with intensity up to 500 suns) without heating (using chopped concentrated sunlight) induces considerable PL enhancement while the optical absorption spectrum remains unchanged. With accurate temperature control, aging under concentrated sunlight results in similar instability trends as that under 1 sun.

The power conversion efficiency of the carbon‐based perovskite solar cells is enhanced by 21.4% simply by interfacial post‐treatment with cesium acetate. The nonencapsulated device can remain stable for 4 months without observable degradation. The improved performance is attributed to the better matched energy levels and the reduced defect density.

The interface between the perovskite layer and carbon electrode is important for printable carbon‐based perovskite solar cells (PSCs) to improve the power conversion efficiency (PCE) and device stability. A series of acetate salts are employed to in situ post‐modify the interface between the perovskite layer and carbon electrode for printable carbon‐based PSCs by the post‐treatment method. Cesium acetate (CsAc) is identified to enhance the average PCE from 12.6% to 15.3%. The stabilized output PCE reaches 15.6%, and the highest open‐circuit voltage (V _OC) is 1.1 V, representing a new milestone in increasing the ratio of V _OC/E _g (E _g: bandgap of perovskite) to be 0.67 for the printable carbon‐based PSCs without hole transporting materials. Moreover, the device stability in air is also improved by CsAc post‐modification. The improved performance is attributed to the better matching of energy levels of the perovskite layer with a carbon electrode and reduced defect density in the perovskite layer via in situ produced methylammonium acetate and ion replacement. This simple and effective CsAc post‐treatment method opens a new promising direction for developing scalable carbon‐based PSCs.

An aggregation‐induced emission (AIE) molecule is successfully employed as an effective hole transport material in an inverted planar perovskite solar cell. The improvement of perovskite crystallinity and the suppression of nonradiative recombination at the AIE/perovskite interface result in enhanced device performance and stability as compared with the poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS)‐based control one.

Organic hole‐transport materials (HTMs) are very promising for perovskite solar cells (PSCs) because the molecule structure is engineered via facile chemical routes. Herein, an aggregation‐induced emission (AIE) molecule, 2‐(2,7‐bis(4‐(bis(4‐methoxyphenyl)amino)phenyl)‐9H‐fluoren‐9‐ylidene)malononitrile (TFM), is successfully employed for the first time as a HTM in an inverted planar PSC, obtaining a promising device performance superior to that of the control device with poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS) HTM. An optimal power conversion efficiency (PCE) of 16.03% is obtained for the TFM‐based PSCs with a J _sc of 22.68 mA cm⁻², V _oc of 0.97 V and FF of 72.9%, while that of the control PEDOT:PSS‐based device is 14.95%. Steady‐state and time‐resolved photoluminescence results reveal suppressed nonradiative recombination at the TFM/perovskite interface that is attributed to the effective passivation of the uncoordinated Pb at the perovskite surface by the CN⁻ groups of TFM molecules, as confirmed by X‐ray photoelectronic spectroscopy measurements. In addition to the passivation, the hydrophobic character of TFM films also contributes to the improved device stability. The findings demonstrate the potential of AIE molecules in PSCs and also paves a novel way to improve device performance and stability by molecular structure engineering of AIE molecules in the future.

A simple dynamic antisolvent quenching process is used for the efficient and reliable fabrications of uniform and high‐quality 10 × 10 cm² large‐area perovskite films. The perovskite module fabricated using this technique achieves an efficiency approaching 18% and a certified efficiency of 17.4% with the aperture area of 53.64 cm².

Perovskite solar cells represent a promising photovoltaic technology, which achieves record power conversion efficiencies over 24%. However, a problem on the commercial processing is the unavoidable efficiency loss during the scalable fabrication of perovskite solar module. The efficient and reliable fabrications of high‐quality large‐area perovskite films guarantee commercialized up‐scaling of perovskite solar cells with high efficiency. Herein, a simple dynamic antisolvent quenching (DAS) process is presented to understand large‐area uniform perovskite films to obtain an efficient perovskite solar module. This method provides a facile and universal approach to fabricate cracks‐free and uniform large‐area mixed‐cation perovskite films. A champion module device (10 × 10 cm²) with efficiency of 17.82% (another module with certified efficiency of 17.4%) is obtained using DAS process.

Carbon stack perovskite solar cells offer potential as a manufacturable architecture using techniques such as screen printing and are characterized by micron‐scale thick active junctions. Herein, an electro‐optical model is developed that explains the working mechanisms of charge generation and collection in these solar cells that not only provides deep insight but also can be used for device optimization.

Mesoporous carbon stack architecture is attracting considerable interest as a candidate for scalable, low‐cost perovskite solar cells amenable to high‐throughput manufacturing. These cells are characterized by microns‐thick mesoporous titania and zirconia layers capped by a nonselective carbon electrode with the whole stack being infused with a perovskite semiconductor. Although the architecture does not deliver the >20% power conversion efficiencies characteristic of perovskite planar and mesoporous geometries, it does produce cells with respectable efficiencies >16%, which is unexpected due to the carbon electrode being a nonideal anode and the active layers being so thick. Optimization of these cells requires an understanding of the coupled efficiencies of light absorption, charge generation, and extraction which is currently unavailable. Herein, a combined experimental‐simulation study that elucidates photogeneration and extraction is reported. By determining the optical constants of the individual components and using effective‐medium approximations, the internal quantum efficiencies (IQE) in both the titania and zirconia layers are determined to be ≈85%. Numerical drift‐diffusion simulations indicate that this high IQE is a consequence of the thick junctions reducing minority carrier concentrations at the electrodes, thereby decreasing surface recombination. This insight can now be used to tune the carbon stack for efficiency and simplicity.

Halide‐ and nonhalide‐based guanidinium salts are explored to study the impact of counterions supplied along with the guanidinium cation on the photophysical properties of perovskite films and photovoltaic performance of perovskite solar cells.

The impacts of halide and nonhalide sources of guanidinium cations, including guanidinium chloride (GCl) ((NH₂)₃CCl) and guanidinium thiocyanate (GTC) ((NH₂)₃CSCN), are comparatively analyzed on the structural, morphological, and photophysical properties of (CsMAFA)PbBr _x I_3 − x (x = 0.17) (MA = methylammonium, FA = formamidinium) perovskite films. X‐ray diffraction (XRD) reveals that the formation of photoinactive phases depends on the nature of counterions (halide vs nonhalide). Furthermore, morphological analysis shows that with the addition of guanidinium salts, the apparent grain size decreases due to the enhancement of nucleation density and/or slow growth of perovskite structures. More importantly, the introduction of GCl leads to the fabrication of perovskite solar cells (PSCs), yielding a photovoltage as high as 1.16 V (1.1 V for reference). In contrast, the introduction of GTC minimally affects the photovoltage, underlining the significance of counterions in improving the photovoltage of PSCs. The present preliminary results of the density functional theory based theoretical investigation related to the effect of G cation on the structure of the perovskite system is presented. In summary, the insights gained through structural and morphological characterization helps to understand the critical role of counterions of guanidinium salts in PSCs.

A simple coalloying strategy is applied to partly substitute HC(NH₂)₂/CH₃NH₃ (FA/MA) and I⁻ in FA_0.85MA_0.15PbI₃ perovskite by Cs⁺ and Ac⁻ respectively, which is an effective way to improve the tolerance factor, crystallinity, electronic properties, and band structure of FA_0.85MA_0.15PbI₃ materials. Consequently, the coalloyed perovskite solar cells yield a champion power conversion efficiency of 21.95% with negligible hysteresis and high stability.

A simple coalloying strategy is applied to improve the efficiency and stability of FA_0.85MA_0.15PbI₃ perovskite solar cells (PSCs) by using cesium acetate (CsAc) as an additive. It is found that the simultaneous incorporation of cation (Cs⁺) and anion (Ac⁻) into the FA_0.85MA_0.15PbI₃ film is an effective approach to realize lattice contraction, grain size enlargement, photoelectric properties improvement, band structure modulation, and therefore the optimization of the efficiency and stability of PSCs. At optimal CsAc alloying, the FA_0.85MA_0.15PbI₃ PSCs achieve a maximum power conversion efficiency (PCE) of 21.95% and an average of over 21%. In addition, the alloyed PSCs retain 97% of their initial PCE values after aging for 55 days in air without encapsulation.