Mahui

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 general amphiphilic star‐like block copolymer nanoreactor strategy for in situ crafting a set of hairy perovskite quantum dots (QDs) with precisely tunable size and exceptionally high water and colloidal stabilities is presented. Intriguingly, the readily alterable length of the permanently bound outer hydrophobic polymers renders remarkable control over the stability enhancement of hairy perovskite QDs.

Abstract

Instability of perovskite quantum dots (QDs) toward humidity remains one of the major obstacles for their long‐term use in optoelectronic devices. Herein, a general amphiphilic star‐like block copolymer nanoreactor strategy for in situ crafting a set of hairy perovskite QDs with precisely tunable size and exceptionally high water and colloidal stabilities is presented. The selective partition of precursors within the compartment occupied by inner hydrophilic blocks of star‐like diblock copolymers imparts in situ formation of robust hairy perovskite QDs permanently ligated by outer hydrophobic blocks via coprecipitation in nonpolar solvent. These size‐ and composition‐tunable perovskite QDs reveal impressive water and colloidal stabilities as the surface of QDs is intimately and permanently ligated by a layer of outer hydrophobic polymer hairs. More intriguingly, the readily alterable length of outer hydrophobic polymers renders the remarkable control over the stability enhancement of hairy perovskite QDs.

The role of cation and halide mixing is revealed using in situ X‐ray scattering measurements during spin‐coating. Modulating the cation/halide composition directly impacts the lifetime of the sol–gel precursor film and its easy and reproducible conversion to the perovskite phase to yield solar cells with 20% power conversion efficiency.

Abstract

Perovskite solar cells increasingly feature mixed‐halide mixed‐cation compounds (FA_{1− x − y} MA _x Cs _y PbI_{3− z} Br_z) as photovoltaic absorbers, as they enable easier processing and improved stability. Here, the underlying reasons for ease of processing are revealed. It is found that halide and cation engineering leads to a systematic widening of the anti‐solvent processing window for the fabrication of high‐quality films and efficient solar cells. This window widens from seconds, in the case of single cation/halide systems (e.g., MAPbI₃, FAPbI₃, and FAPbBr₃), to several minutes for mixed systems. In situ X‐ray diffraction studies reveal that the processing window is closely related to the crystallization of the disordered sol–gel and to the number of crystalline byproducts; the processing window therefore depends directly on the precise cation/halide composition. Moreover, anti‐solvent dripping is shown to promote the desired perovskite phase with careful formulation. The processing window of perovskite solar cells, as defined by the latest time the anti‐solvent drip yields efficient solar cells, broadened with the increasing complexity of cation/halide content. This behavior is ascribed to kinetic stabilization of sol–gel state through cation/halide engineering. This provides guidelines for designing new formulations, aimed at formation of the perovskite phase, ultimately resulting in high‐efficiency perovskite solar cells produced with ease and with high reproducibility.

Defects in metal halide perovskites contribute to nonradiative recombination of photo‐carriers. On device level, such recombination undesirably inflates the open‐circuit voltage deficit and acts as a significant roadblock toward the theoretical efficiency limit of 30% perovskite solar cells. Such voltage‐limiting mechanisms are assessed by focusing on their origin and possible mitigation strategies.

Abstract

Metal‐halide perovskites are rapidly emerging as an important class of photovoltaic absorbers that may enable high‐performance solar cells at affordable cost. Thanks to the appealing optoelectronic properties of these materials, tremendous progress has been reported in the last few years in terms of power conversion efficiencies (PCE) of perovskite solar cells (PSCs), now with record values in excess of 24%. Nevertheless, the crystalline lattice of perovskites often includes defects, such as interstitials, vacancies, and impurities; at the grain boundaries and surfaces, dangling bonds can also be present, which all contribute to nonradiative recombination of photo‐carriers. On device level, such recombination undesirably inflates the open‐circuit voltage deficit, acting thus as a significant roadblock toward the theoretical efficiency limit of 30%. Herein, the focus is on the origin of the various voltage‐limiting mechanisms in PSCs, and possible mitigation strategies are discussed. Contact passivation schemes and the effect of such methods on the reduction of hysteresis are described. Furthermore, several strategies that demonstrate how passivating contacts can increase the stability of PSCs are elucidated. Finally, the remaining key challenges in contact design are prioritized and an outlook on how passivating contacts will contribute to further the progress toward market readiness of high‐efficiency PSCs is presented.

2‐Thiophenemethylammonium spacer cations are successfully embedded into formamidinium iodide (FAI)‐ and methylammonium iodide (MAI)‐based 3D perovskites, and these cations can induce the crystalline growth and orientation of the obtained 2D/3D hybrid perovskite. A champion efficiency of 21.49% is demonstrated for a 2D/3D perovskite device, which is combined with a dramatically improved stability in comparison with that of the control device.

Abstract

Highly efficient and stable 2D/3D hybrid perovskite solar cells using 2‐thiophenemethylammonium (ThMA) as the spacer cation are successfully demonstrated. It is found that the incorporation of ThMA spacer cation into 3D perovskite, which forms a 2D/3D hybrid structure, can effectively induce the crystalline growth and orientation, passivate the trap states, and hinder the ion motion, resulting in improved carrier lifetime and reduced recombination losses. The optimized device exhibits a power conversion efficiency (PCE) of 21.49%, combined with a high V _OC of 1.16 V and a notable fill factor (FF) of 81%. More importantly, an encapsulated 2D/3D hybrid perovskite device sustains ≈99% of its initial PCE after 1680 h in the ambient atmosphere, whereas the control 3D perovskite device drops to ≈80% of the original performance. Importantly, the device stability under continuous light soaking (100 mW cm⁻²) is enhanced significantly for 2D/3D perovskite device in comparison with that of the control device. These results reveal excellent photovoltaic properties and intrinsic stabilities of the 2D/3D hybrid perovskites using ThMA as the spacer cation.

Highly air‐stable PbSe colloidal quantum dots (CQDs) are produced via an in situ chloride and cadmium passivation technique. A high‐quality film is fabricated using solution‐phase ligand exchange and a one‐step deposition method. By using a PbS‐EDT (EDT = 1,2‐ethanedithiol) hole‐transporting layer, a PbI₂‐capped PbSe‐CQD‐based photovoltaic device shows a record efficiency of 10.68% with impressive air and light soaking stability.

Abstract

Low‐cost solution‐processed lead chalcogenide colloidal quantum dots (CQDs) have garnered great attention in photovoltaic (PV) applications. In particular, lead selenide (PbSe) CQDs are regarded as attractive active absorbers in solar cells due to their high multiple‐exciton generation and large exciton Bohr radius. However, their low air stability and occurrence of traps/defects during film formation restrict their further development. Air‐stable PbSe CQDs are first synthesized through a cation exchange technique, followed by a solution‐phase ligand exchange approach, and finally absorber films are prepared using a one‐step spin‐coating method. The best PV device fabricated using PbSe CQD inks exhibits a reproducible power conversion efficiency of 10.68%, 16% higher than the previous efficiency record (9.2%). Moreover, the device displays remarkably 40‐day storage and 8 h illuminating stability. This novel strategy could provide an alternative route toward the use of PbSe CQDs in low‐cost and high‐performance infrared optoelectronic devices, such as infrared photodetectors and multijunction solar cells.

In article no. 1900045, Hong Liu, Wenzhong Shen, and co‐workers employ a controllable ultraviolet/ozone (UVO) treatment to prepare a high‐quality electrochemically deposited NiO_x hole transport layer (HTL). Under optimal conditions of UVO treatment, the increased hole conductivity in the HTL, reduced interface defects, and narrowed offset of the valence band between HTL and perovskite film result in high‐performing perovskite solar cells with an efficiency of 19.67%.

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 found to be exceptionally susceptible to potential‐induced degradation (PID) with performance losses up to 95% after 18 h of high‐voltage stress. Still, most of the lost performance can be regained by reversing the polarity of the applied high voltage.

In recent years, metal halide perovskite solar cells have become a major competitor in the run to lower the levelized cost of electricity (LCOE) of photovoltaic (PV) systems. Commercialization of this new technology mainly depends on the long‐term stability of such devices, for which potential‐induced degradation (PID) may represent a factor of detrimental impact. As PID can trigger rapid and significant losses in PV systems, it is generally considered among the most critical failure modes with a high financial repercussion. Herein, the results of PID tests on perovskite solar cells are reported for the very first time. The solar cells are found to be extremely susceptible to PID: 18 h of high‐voltage stress, according to the PID test standard IEC 62804‐1 TS (foil method at 60 °C), shows a performance degradation of up to 95%, which mainly results from a decrease in the short‐circuit current. These results also uncover near full PID recoverability and pave the way toward further research into its mechanisms, kinetics, and mitigation.

A kinetically enduring Lewis acid–base reaction between the additives from the solution‐processed hole‐transport layer occurs, and perovskite manipulates both the energy‐band alignment and the charge transfer at the interface, accounting for the short‐term evolution of figures of merit in perovskite solar cells.

Device stability is the most important issue that hinders perovskite solar cell (PSC) commercialization, given the achieved efficiency of PSC that exceeds 23%. The perovskite materials and contact layers throughout the device stack are scrutinized with regard to stability, but research has mainly focused on the examination of long‐term behavior. Herein, the impacts on the short‐term stability of PSCs, which are always overlooked, are investigated. The short‐term stability of the PSCs is correlated to the additives of the solution‐processed hole‐transport layer. These additives exert a critical impact underneath the perovskite layer. A kinetically enduring Lewis acid–base reaction between the additives and the perovskite manipulates both the energy‐band alignment and the charge transfer at the interface, accounting for short‐term evolution of figures of merit in PSCs. Our revelation of the impacts on the short‐term stability of PSCs calls for a re‐evaluation of interface modification induced by solution‐process engineering, thereby compensating for the overall device stability and allowing for progress toward commercialization.

Sulfur‐incorporated bismuth‐based perovskite films are obtained by a low‐pressure vapor‐assisted solution process (LP‐VASP) method. A homogeneous and highly compact MBI film with a narrower bandgap of 1.67 eV is successfully achieved. In addition, the obtained film has a low trap‐state density of 1.9 × 10¹⁶ cm⁻³ and the optimal PCE of MA₃Bi₂I_9‐2x S _x PSCs reached 0.152%.

Methylammonium (MA) bismuth iodide ((CH₃NH₃)₃Bi₂I₉) is a promising perovskite material for solar cell application considering the air stability and the nontoxic lead‐free molecular constitution. However, the further improvement of the device performances is prohibited by the wide bandgap (≈2.1 eV) and unsatisfied crystallinity of the (CH₃NH₃)₃Bi₂I₉ films. Herein, a developed low‐pressure vapor‐assisted solution process (LP‐VASP) method is applied to obtain the sulfur‐incorporated bismuth‐based perovskites films. Due to the presence of sulfur, both the crystal quality and the energy band property are improved effectively in the as‐fabricated lead‐free perovskite films. After a systematic study of the influence of the reaction time on the device performances, the optimized reaction time is found to be 30 min, under which, the sulfur‐incorporated MA₃Bi₂I_9‐2x S _x perovskite films exhibit a reduced bandgap of 1.67 eV and a compact morphology. The corresponding optimal PCE reaches 0.152%. This study provides a new way for the incorporation of sulfur in the lead‐free bismuth‐based perovskite solar cells.

Photostability is one of the most vital challenges for perovskite solar cells (PSCs). With the embedding of black phosphorus (BP), well known for its self‐healing and superior property to regulate charge recombination, into MAPbI₃ perovskites, the associated devices exhibit significant enhancement in photostability. The incorporation of BP effectively inhibits Pb⁰ defect formation and retards hot carrier recombination.

Photostability is one of the most vital challenges for organic–inorganic hybrid perovskite solar cells (PSCs). With the incorporation of black phosphorus (BP), well known for self‐healing and its superior property to regulate charge recombination, into CH₃NH₃PbI₃ perovskites (MAPbI₃/BP), the associated PSCs exhibit significant enhancement in photostability in addition to the photovoltaic (PV) performance. The MAPbI₃/BP‐based PSCs retain ≈94% of initial efficiency after 1000 h continuous white light LED illumination in a dry N₂ glovebox whereas their counterparts without the incorporation of BP decrease to ≈30%. Although BP has very small influence on the morphology and structure of the perovskite crystals, Pb⁰ defects are effectively inhibited and hot carrier recombination is found to be retarded as confirmed by femtosecond optical spectroscopy. The utilization of the material to simultaneously inhibit Pb⁰ defect formation and retard charge recombination, such as BP, is a promising strategy to enhance the photostability of organic–inorganic hybrid perovskite‐based PSCs and their siblings.

Chlorine‐substituted graphdiyne (ClGD) is employed into electron transport layers of MAPbI₃‐based perovskite solar cells. It is experimentally and theoretically demonstrated that the interactions of derivated graphdiyne and PCBM stem from four types of noncovalent bonds, which contribute to the improved device performance. Perovskite solar cells based on the ClGD‐PCBM obtain an enhanced power conversion efficiency (PCE) of 20.34%.

Chlorine‐substituted graphdiyne (ClGD) is employed into electron transport layers (ETLs) of MAPbI₃‐based perovskite solar cells for the first time, forming a high‐quality film with superior film morphology and electrical conductivity as compared with pristine [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) film. Strikingly, a champion power conversion efficiency of 20.34% is achieved, showing a 19% enhancement compared with the counterparts (17.08%). Simultaneously, ClGD‐PCBM‐based devices show suppressed J–V hysteresis. It is experimentally and theoretically demonstrated that the interactions of derivated graphdiyne and PCBM stem from four types of noncovalent bonds, which contribute to the improved device performance. The results suggest that derivated graphdiyne‐based interfacial material is promising for the applications in solar cells and other photoelectric devices.

The recent progress in lead‐free tin (Sn)‐based perovskite solar cells (PSCs) is reviewed. After briefing the structural and optoelectronic properties of Sn‐based perovskites, the film deposition methods and the strategies toward high performance in Sn‐based PSCs are then summarized. The challenges and prospective opportunities in this field are also discussed.

Perovskite solar cells (PSCs) have achieved state‐of‐the‐art efficiency, approaching monocrystalline silicon solar cells due to the superior optoelectronic properties and intensive research efforts, fulfilling its forthcoming commercial use at affordable costs. Nevertheless, the toxicity of lead (Pb) is still one of the obstacles hindering future large‐scale production. Herein, the recent progress of emerging lead‐free tin (Sn)‐based PSCs is reviewed. First, the structural and photovoltaic‐related properties of Sn‐based perovskites are summarized. Following a brief introduction of film deposition methods, strategies recently adopted to obtain high performance are then discussed in detail. Finally, the current challenges and prospective opportunities are provided to help the further progression of Sn‐based PSCs.

Compared with the traditional vacuum vapor deposition method, the sputtering‐deposited electrode has smoother surface, negligible pin‐hole, less material consumption, and can be used in large‐area fabrication. Through the interface modification of Au/Spiro‐OMeTAD, the perovskite solar cells (PSCs) with direct‐current (DC) magnetron sputtering‐deposited gold electrode achieve a high efficiency of 18.32%.

Perovskite solar cells (PSCs) attract great attention due to their low cost and high efficiency. In general, the Au cathode, a key component in PSCs, is prepared via an uneconomic vacuum thermal deposition method. Instead, the sputtering deposition method is much more economic and faster. However, it is generally thought that the organic hole transport layer such as 2,2′,7,7′‐tetrakis[N,N‐di(4‐methoxyphenyl)amino]‐9,9′‐spirobifluorene (Spiro‐OMeTAD) can be easily damaged by the high energy plasma during the sputtering process. Thus, the performance of the PSCs greatly decreases. Herein, the structure of the planar PSCs is carefully manipulated by matching the thickness of Spiro‐OMeTAD layer and the Au film. With the further engineering of the interface of the Au/Spiro‐OMeTAD, the planar PSCs with the sputtered Au cathode exhibit a highly reproducible average efficiency of 17.6% ± 0.8%, with the best efficiency of 18.3%. In addition, the Cu electrode is demonstrated by the sputtering method. Finally, the Au sputter deposition is scaled up to make a high efficiency (14.7%) 10 × 10 cm² module. This demonstrates well that the sputtering deposition of the metal cathode is an effective way for the fabrication of high efficient PSCs for future industrialization.

An aggregation‐breaking strategy to inhibit the trend of self‐aggregation of benzo[1,2‐b:4,5‐b']difuran (BDF)‐based polymers, the power conversion efficiency (PCE, 12.42%) with a high fill factor (FF, 75.19%) is obtained, which is higher than that of PBDTTz‐SBP:ITIC‐based devices. This proposed strategy may be a good choice to surpass the benzo[1,2‐b:4,5‐b']dithiophene (BDT)‐based polymers and obtain the state‐of‐the‐art photovoltaic materials.

Great efforts have been devoted to semiconductive polymers based on the benzo[1,2‐b:4,5‐b’]dithiophene (BDT) unit, and great progress has been achieved in organic solar cells, whereas the analogue core benzo[1,2‐b:4,5‐b’]difuran (BDF) has the similar extended planar structure, and the electronic structure gets less development in the photovoltaic system. Herein, a novel BDF core‐based copolymer PBDFTz‐SBP is synthesized, which decorates with two 2D extended biphenyl side chains and shows a relatively small polymer segments distortion and strong intermolecular π–π interaction in relation to the BDT‐based polymer. Using this polymer, an aggregation‐breaking strategy to suppress the trend of self‐aggregation of polymers’ segment is proposed, which obtains an appropriate phase separation and forms favorable bicontinuous interpenetrating networks for charge transport. It is found that PBDFTz‐SBP:ITIC achieves an excellent power‐conversion efficiency (PCE) of 12.42% with an open‐circuit voltage (V _OC) of 0.89 V, a short‐circuit current density (J _SC) of 18.56 mA cm⁻², and a high fill factor (FF) of 75.19% when the spin‐coating solution is 120 °C, which is higher than that of PBDTTz‐SBP:ITIC‐based devices even under optimized conditions. This proposed strategy may be a good choice for the BDF unit to construct the donor (D)–acceptor (A) type polymers and surpass the counterpart BDT‐based photovoltaic materials and obtain a state‐of‐the‐art PCEs.

The recent progress in double‐metallic lead‐free perovskite materials and devices is comprehensively reviewed. In particular, theory calculation, electronic structure, and fundamental properties of double perovskites are deliberated. The achievements and challenges in their application including solar cells, photon detectors, and laser devices, are summarized. In addition, the viewpoints for future research of this class of perovskites are also provided.

Lead halide perovskite (ABX₃) has attracted considerable attention due to its applicability as absorber layers in highly efficient photovoltaic cells. With regard to the lead toxicity, double‐metallic lead‐free perovskite, A₂B^IB^IIIX₆, in which the neighboring B⁺ and B³⁺ sites in the crystal microstructure are alternately occupied by monovalent‐metal and trivalent‐metal cations, is regarded to be a promising alternative to the widely used lead‐based perovskites. This review aims to summarize the recent advances in the new class of A₂B^IB^IIIX₆ double‐metallic lead‐free perovskites. In particular, the electronic structure, synthesis, property, and their applications in devices, for example, photovoltaics, photodetectors, and light emitting diodes, is carefully classified and presented. Notably, the theoretical calculations point out that there is much room toward potential applications for this new class of perovskite materials. The present review provides a holonomic conclusion and opens new perspectives toward realizing higher performance of A₂B^IB^IIIX₆‐based devices.

2‐Thiophenemethylammonium spacer cations are successfully embedded into formamidinium iodide (FAI)‐ and methylammonium iodide (MAI)‐based 3D perovskites, and these cations can induce the crystalline growth and orientation of the obtained 2D/3D hybrid perovskite. A champion efficiency of 21.49% is demonstrated for a 2D/3D perovskite device, which is combined with a dramatically improved stability in comparison with that of the control device.

Abstract

Highly efficient and stable 2D/3D hybrid perovskite solar cells using 2‐thiophenemethylammonium (ThMA) as the spacer cation are successfully demonstrated. It is found that the incorporation of ThMA spacer cation into 3D perovskite, which forms a 2D/3D hybrid structure, can effectively induce the crystalline growth and orientation, passivate the trap states, and hinder the ion motion, resulting in improved carrier lifetime and reduced recombination losses. The optimized device exhibits a power conversion efficiency (PCE) of 21.49%, combined with a high V _OC of 1.16 V and a notable fill factor (FF) of 81%. More importantly, an encapsulated 2D/3D hybrid perovskite device sustains ≈99% of its initial PCE after 1680 h in the ambient atmosphere, whereas the control 3D perovskite device drops to ≈80% of the original performance. Importantly, the device stability under continuous light soaking (100 mW cm⁻²) is enhanced significantly for 2D/3D perovskite device in comparison with that of the control device. These results reveal excellent photovoltaic properties and intrinsic stabilities of the 2D/3D hybrid perovskites using ThMA as the spacer cation.

A general amphiphilic star‐like block copolymer nanoreactor strategy for in situ crafting of a set of hairy perovskite quantum dots (QDs) with precisely tunable size and exceptionally high water and colloidal stabilities is presented. Intriguingly, the readily alterable length of the permanently bound outer hydrophobic polymers renders remarkable control over the stability enhancement of hairy perovskite QDs.

Abstract

Instability of perovskite quantum dots (QDs) toward humidity remains one of the major obstacles for their long‐term use in optoelectronic devices. Herein, a general amphiphilic star‐like block copolymer nanoreactor strategy for in situ crafting a set of hairy perovskite QDs with precisely tunable size and exceptionally high water and colloidal stabilities is presented. The selective partition of precursors within the compartment occupied by inner hydrophilic blocks of star‐like diblock copolymers imparts in situ formation of robust hairy perovskite QDs permanently ligated by outer hydrophobic blocks via coprecipitation in nonpolar solvent. These size‐ and composition‐tunable perovskite QDs reveal impressive water and colloidal stabilities as the surface of QDs is intimately and permanently ligated by a layer of outer hydrophobic polymer hairs. More intriguingly, the readily alterable length of outer hydrophobic polymers renders the remarkable control over the stability enhancement of hairy perovskite QDs.

The role of cation and halide mixing is revealed using in situ X‐ray scattering measurements during spin‐coating. Modulating the cation/halide composition directly impacts the lifetime of the sol–gel precursor film and its easy and reproducible conversion to the perovskite phase to yield solar cells with 20% power conversion efficiency.

Abstract

Perovskite solar cells increasingly feature mixed‐halide mixed‐cation compounds (FA_{1− x − y} MA _x Cs _y PbI_{3− z} Br_z) as photovoltaic absorbers, as they enable easier processing and improved stability. Here, the underlying reasons for ease of processing are revealed. It is found that halide and cation engineering leads to a systematic widening of the anti‐solvent processing window for the fabrication of high‐quality films and efficient solar cells. This window widens from seconds, in the case of single cation/halide systems (e.g., MAPbI₃, FAPbI₃, and FAPbBr₃), to several minutes for mixed systems. In situ X‐ray diffraction studies reveal that the processing window is closely related to the crystallization of the disordered sol–gel and to the number of crystalline byproducts; the processing window therefore depends directly on the precise cation/halide composition. Moreover, anti‐solvent dripping is shown to promote the desired perovskite phase with careful formulation. The processing window of perovskite solar cells, as defined by the latest time the anti‐solvent drip yields efficient solar cells, broadened with the increasing complexity of cation/halide content. This behavior is ascribed to kinetic stabilization of sol–gel state through cation/halide engineering. This provides guidelines for designing new formulations, aimed at formation of the perovskite phase, ultimately resulting in high‐efficiency perovskite solar cells produced with ease and with high reproducibility.