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We constructed the high-quality perovskite films with bottom-up n–p homojunctions via a modified sequential two-step deposition technique, which optimized the energy level alignment between the perovskite layer and the adjacent contacts for promoting charge separation and extraction, as well as suppressing non-radiative recombination. The resultant n–p homojunction-based electron transport layer-free perovskite solar cells achieved improved efficiency, which was ∼13% higher than that of the control counterpart. [ABSTRACT FROM AUTHOR]

Photoactive black‐phase formamidinium lead triiodide (α‐FAPbI3) perovskite has dominated the prevailing high‐performance perovskite solar cells (PSCs), normally for those spin‐coated, conventional n‐i‐p structured devices. Unfortunately, α‐FAPbI3 has not been made full use of its advantages in inverted p‐i‐n structured PSCs fabricated via blade‐coating techniques owing to uncontrollable crystallization kinetics and complicated phase evolution of FAPbI3 perovskites during film formation. Herein, a customized crystal surface energy regulation strategy has been innovatively developed by incorporating 0.5 mol % of N‐aminoethylpiperazine hydroiodide (NAPI) additive into α‐FAPbI3 crystal‐derived perovskite ink, which enabled the formation of highly‐oriented α‐FAPbI3 films. We deciphered the phase transformation mechanisms and crystallization kinetics of blade‐coated α‐FAPbI3 perovskite films via combining a series of in‐situ characterizations and theoretical calculations. Interestingly, the strong chemical interactions between the NAPI and inorganic Pb−I framework help to reduce the surface energy of (100) crystal plane by 42 %, retard the crystallization rate and lower the formation energy of α‐FAPbI3. Benefited from multifaceted advantages of promoted charge extraction and suppressed non‐radiative recombination, the resultant blade‐coated inverted PSCs based on (100)‐oriented α‐FAPbI3 perovskite films realized promising efficiencies up to 24.16 % (~26.5 % higher than that of the randomly‐oriented counterparts), accompanied by improved operational stability. This result represented one of the best performances reported to date for FAPbI3‐based inverted PSCs fabricated via scalable deposition methods. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) have experienced exceptional development in recent years, due to their outstanding photoelectronic properties and low‐cost solution processing. Many state‐of‐the‐art PSC designs have been effectively demonstrated using a stacked 3D perovskite/2D perovskite heterostructure, yet limitations arise due to the low conductivity of the 2D perovskite, the hidden buried interface of 3D perovskite, and halide ion migration within 3D/2D PSC device under operational bias. Here, these limitations are overcome by developing a novel and universal post‐synthetic metal (Zn2+) doping strategy and realizing 3D/2D PSCs with superior efficiency and stability. Informed by ab initio calculations and synchrotron fine structure experiments, it is revealed that the introduced zinc ions are energetically favored at interstitial crystal sites, subsequently hindering the migration of halide ions and producing a beneficial shift toward a more n‐type character in the buried 3D perovskite interface. Combined with extensive photophysical characterization, the Zn2+‐modified 3D/2D perovskite thin film is shown to strongly recover its photo‐carrier conductivity compared with the 3D/2D perovskite film, boosting the efficiency (22.90%) of PSCs while exhibiting improved humidity and operational stability. [ABSTRACT FROM AUTHOR]

State‐of‐the‐art, high‐performance solar cells and light‐emitting diodes normally rely on tedious layer‐by‐layer sequential deposition of carrier transport layer and light‐absorbing/emitting layers, which is not cost‐effective. Several recent exciting works have demonstrated surprising breakthroughs in terms of simplified processing of these optoelectronic devices. Upon the incorporation of carbazole phosphonic acid molecules and their derivatives into precursor ink beforehand, charge‐selective contact could spontaneously self‐assemble at the buried interface between the conducting substrate and photoactive layer, which results in the construction of simplified‐structured devices that yield comparable optoelectronic performances to the conventionally fabricated devices with full architectures. Herein, the recent groundbreaking advancement of high‐performance optoelectronic devices fabricated via a convenient codeposition technique is summarized, with particular emphasis on elucidating the chemical mechanism of self‐assembly mode and highlighting the unique advantages of this strategy on crystallization regulation, targeted defect passivation, carrier dynamics modulation, and comprehensive device performance improvement. Finally, the associated challenges are critically discussed and the future research directions are insightfully proposed, which can revolutionize the pathway toward constructing highly efficient optoelectronic devices in a cost‐effective manner and setting forward to future commercialization. [ABSTRACT FROM AUTHOR]

Sn perovskite solar cells have been regarded as one of the most promising alternatives to the Pb‐based counterparts due to their low toxicity and excellent optoelectronic properties. However, the Sn perovskites are notorious to feature heavy p‐doping characteristics and possess abundant vacancy defects, which result in under‐optimized interfacial energy level alignment and severe nonradiative recombination. Here, we reported a synergic "electron and defect compensation" strategy to simultaneously modulate the electronic structures and defect profiles of Sn perovskites via incorporating a traced amount (0.1 mol %) of heterovalent metal halide salts. Consequently, the doping level of modified Sn perovskites was altered from heavy p‐type to weak p‐type (i.e. up‐shifting the Fermi level by ~0.12 eV) that determinately reducing the barrier of interfacial charge extraction and effectively suppressing the charge recombination loss throughout the bulk perovskite film and at relevant interfaces. Pioneeringly, the resultant device modified with electron and defect compensation realized a champion efficiency of 14.02 %, which is ~46 % higher than that of control device (9.56 %). Notably, a record‐high photovoltage of 1.013 V was attained, corresponding to the lowest voltage deficit of 0.38 eV reported to date, and narrowing the gap with Pb‐based analogues (~0.30 V). [ABSTRACT FROM AUTHOR]

The 2D/3D perovskite heterostructures have been widely investigated to enhance the efficiency and stability of perovskite solar cells (PSCs). However, rational manipulation of phase distribution and energy level alignment in such 2D/3D perovskite hybrids are still of great challenge. Herein, we successfully achieved spontaneous phase alignment of 2D/3D perovskite heterostructures by concurrently introducing both 2D perovskite component and organic halide additive. The graded phase distribution of 2D perovskites with different n values and 3D perovskites induced favorable energy band alignment across the perovskite film and boosted the charge transfer at the relevant heterointerfaces. Moreover, the 2D perovskite component also acted as a "band‐aid" to simultaneously passivate the defects and release the residual tensile stress of perovskite films. Encouragingly, the blade‐coated PSCs based on only ≈2 s in‐situ fast annealed 2D/3D perovskite films with favorable energy funnels and toughened heterointerfaces achieved promising efficiencies of 22.5 %, accompanied by extended lifespan. To our knowledge, this is the highest reported efficiency for the PSCs fabricated with energy‐saved thermal treatment just within a few seconds, which also outperformed those state‐of‐the‐art annealing‐free analogues. Such a two‐second‐in‐situ‐annealing technique could save the energy cost by up to 99.6 % during device fabrication, which will grant its low‐coast implementation. [ABSTRACT FROM AUTHOR]

The perovskite solar cells (PSCs) are promising for commercialization and practical application. However, high‐quality perovskite films are normally fabricated in inert gas‐filled glovebox, followed by thermal annealing, which is energy‐consuming and thus not cost‐effective. In this study, a simple manufacturing strategy is demonstrated to fabricate the highly‐crystalline perovskite films in ambient air (a relative humidity of over ≈50%) at room temperature via blade‐coating without the subsequent thermal–annealing. The perovskite precursor chemistry is tailored by solvent engineering via employing 2‐methoxyethanol, which can strongly coordinate with ammonium halide species, thus forming highly uniform small‐sized colloids and facilitating the homogeneous nucleation and rapid crystallization of perovskite films even at room temperature. The resultant PSCs fabricated with ambient‐processed, annealing‐free MAPbI3 perovskite films exhibit a champion efficiency up to 19.16% with negligible hysteresis and improved reproducibility, which is on par with the high‐temperature annealed counterparts fabricated in N2, and represented one of the highest reported efficiencies for the room‐temperature processed PSCs in ambient air. The unencapsulated devices show extended lifespan over 1000 h with nearly no efficiency loss. [ABSTRACT FROM AUTHOR]

Mixed‐cation, small band‐gap perovskites via rationally alloying formamidinium (FA) and methylammonium (MA) together have been widely employed for blade‐coated perovskite solar cells with satisfied efficiencies. One of the stringent challenges lies in difficult control of the nucleation and crystallization kinetics of the perovskites with mixed ingredients. Herein, a pre‐seeding strategy by mixing FAPbI3 solution with pre‐synthesized MAPbI3 microcrystals has been developed to smartly decouple the nucleation and crystallization process. As a result, the time window of initialized crystallization has been greatly extended by 3 folds (i.e. from 5 s to 20 s), which enables the formation of uniform and homogeneous alloyed‐FAMA perovskite films with designated stoichiometric ratios. The resultant blade‐coated solar cells achieved a champion efficiency of 24.31 % accompanied by outstanding reproducibility with more than 87 % of the devices showing efficiencies higher than 23 %. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) have witnessed an unprecedentedly rapid development, especially in terms of power conversion efficiency (PCE). However, the solution‐processed perovskite films inevitably possess numerous crystallographic defects (e.g., halide vacancies), which has been shown to incur non‐radiative charge recombination and ion migration, thus limiting the enhancement of the PCE and stability of PSCs. Here, a novel dual metal (i.e., divalent and monovalent metal ions) modification strategy is reported for simultaneously reducing the defects, immobilizing the halide anions, and preventing ion loss from perovskite during post‐annealing process. Accordingly, this strategy significantly reduces non‐radiative recombination, enhancing the PCE by ≈12% and mitigating the current density‐voltage (J–V) hysteresis effect in resultant devices compared to undoped counterparts. As a result, a champion PCE exceeding 22% and a high open‐circuit voltage (Voc) of 1.16 V is obtained for dual metal ions‐modified PSCs. The optimized devices also exhibit extended lifespan upon the dual metal treatment. The study provides a new defect engineering strategy toward more efficient and stable perovskite photovoltaics. [ABSTRACT FROM AUTHOR]

Tin‐based perovskite solar cells (Sn‐PSCs) have emerged as promising environmentally viable photovoltaic technologies, but still suffer from severe non‐radiative recombination loss due to the presence of abundant deep‐level defects in the perovskite film and under‐optimized carrier dynamics throughout the device. Herein, we healed the structural imperfections of Sn perovskites in an "inside‐out" manner by incorporating a new class of biocompatible chelating agent with multidentate claws, namely, 2‐Guanidinoacetic acid (GAA), which passivated a variety of deep‐level Sn‐related and I‐related defects, cooperatively reinforced the passivation efficacy, released the lattice strain, improved the structural toughness, and promoted the carrier transport of Sn perovskites. Encouragingly, an efficiency of 13.7 % with a small voltage deficit of ≈0.47 V has been achieved for the GAA‐modified Sn‐PSCs. GAA modification also extended the lifespan of Sn‐PSCs over 1200 hours. [ABSTRACT FROM AUTHOR]

Perovskite photovoltaics have witnessed overwhelming success over the past decade. Carbon‐based perovskite solar cells (C‐PSCs), using carbon materials as electrodes, make the perovskite photovoltaics more attractive than ever. Since its first launch in 2013, the development of state‐of‐the‐art C‐PSCs has made remarkable achievements in various aspects. Herein, the recent ground‐breaking advancement of C‐PSCs has been summarized, with a particular focus on highlighting the unique advantages of carbon electrodes that enable perovskite photovoltaics affordable, fully printable, and durable. Limitations and challenges associated with C‐PSCs are discussed. An insightful perspective regarding future research directions is provided, revolutionizing the pathway toward new‐generation photovoltaics and optoelectronics. [ABSTRACT FROM AUTHOR]

Room temperature‐processed electron transport layers (RT‐ETLs) demonstrate vast potential to be used in fabricating high‐performance flexible perovskite solar cells (PSCs) in an energy‐saving manner. However, the RT‐ETL normally suffers from inferior crystallinity, mismatched energy level, and high surface trap‐state density, which would result in under‐optimized interfacial electron extraction and undesirable interfacial charge recombination at ETL/perovskite interface, thus limiting the device performance. Herein, a novel strategy is demonstrated to prepare annealing‐free RT‐ETL based on precrystalline metal ion‐modified SnO2 nanocrystals, which perfectly optimizes the interfacial energy level alignment between ETL and perovskite layer, achieving nearly zero‐barrier charge transfer at the interface. As a result, the charge extraction has been remarkably accelerated and the interfacial charge recombination has been largely suppressed, leading to a ≈26% enhancement in device efficiency. The best‐performing flexible PSCs achieve efficiencies up to 19.3%, accompanied by outstanding mechanical strength under repeated bending cycle tests, which, to the best of the knowledge, is one of the highest reported values for the flexible perovskite photovoltaics fabricated with RT‐ETLs. [ABSTRACT FROM AUTHOR]

Simplified perovskite solar cells (PSCs) were fabricated with the perovskite layer sandwiched and encapsulated between carbon‐based electron transport layer (ETL) and counter electrode (CE) by a fully blade‐coated process. A self‐assembled monolayer of amphiphilic silane (AS) molecules on transparent conducting oxide (TCO) substrate appeals to the fullerene ETL deposition and preserves its integrity against the solvent damage. The AS serves as a "molecular glue" to strengthen the adhesion toughness at the TCO/ETL interface via robust chemical interaction and bonding, facilitating the interfacial charge extraction, increasing PCEs by 77 % and reducing hysteresis. A PCE of 18.64 % was achieved for the fully printed devices, one of the highest reported for carbon‐based PSCs. AS‐assisted interfacial linkage and carbon‐material‐assisted self‐encapsulation enhance the stability of the PSCs, which did not experience performance degradation when stored at ambient conditions for over 3000 h. [ABSTRACT FROM AUTHOR]

In this research highlight, recent significant advances with hot‐assisted blade‐coating or air knife‐assisted blade‐coating of different perovskite compositions with bandgaps ranging from 1.3 eV to 1.9 eV (i.e. wide‐bandgap or small‐bandgap perovskites with mixed cations and anions, 2D/3D perovskites, Pb/Sn binary perovskites, and all‐inorganic perovskites) for single‐junction or tandem PSCs are discussed, with an emphasis on elucidating the distinct ink formulation engineering strategies, crystal growth mechanisms, crystallization kinetics, and optoelectronic properties of the different perovskite compositions. [ABSTRACT FROM AUTHOR]

High‐efficiency perovskite solar cells (PSCs) and organic solar cells (OSCs) are promising alternatives for silicon‐based solar cells. At present, the key point for commercialization of PSCs and OSCs is realizing large‐scale production while maintaining the same high efficiency as small‐area ones. In this review, the blade‐coating method for preparing large‐area films is introduced first and the recent advances of blade‐coated OSCs and PSCs are summarized. Then, the effects of blading parameters on the crystal growth and film formation of the light‐harvesting materials are discussed. Moreover, the limitations and advantages of making high‐quality films via blade‐coating are discussed. Finally, some strategies for the up‐scaling of solar cells via blade‐coating are proposed. [ABSTRACT FROM AUTHOR]

The state‐of‐the‐art high‐performance perovskite solar cells (PSCs) with inverted p‐i‐n device structure normally use crystalline metal oxide materials or organic small molecules as the cathode interlayer between the fullerene layer and metal electrode. However, these interlayers are made by either high‐temperature or complicated vacuum‐assisted fabrication process, and in many cases, they are not efficient and effective enough to simultaneously extract the electrons and suppress the interfacial charge recombination. Herein, for the first time, a facile low‐temperature solution‐processed strategy is demonstrated to fabricate an amorphous metal oxyhydroxide (a‐MOH) thin film, which is used as a robust cathode interlayer in inverted PSCs. The a‐MOH interlayer not only facilitates electron extraction and collection via "energy‐favorable" electron tunneling, but also suppresses the interfacial charge recombination via effective hole blocking and electron backflow inhibition. As a result, the PSCs based on a‐MOH interlayer achieve a stabilized power conversion efficiency (PCE) of 21.1% and retain 93% of initial PCE after continuous one‐sun illumination for 500 hours. [ABSTRACT FROM AUTHOR]

The performances of electron‐transport‐layer (ETL)‐free perovskite solar cells (PSCs) are still inferior to ETL‐containing devices. This is mainly due to severe interfacial charge recombination occurring at the transparent conducting oxide (TCO)/perovskite interface, where the photo‐injected electrons in the TCO can travel back to recombine with holes in the perovskite layer. Herein, we demonstrate for the first time that a non‐annealed, insulating, amorphous metal oxyhydroxide, atomic‐scale thin interlayer (ca. 3 nm) between the TCO and perovskite facilitates electron tunneling and suppresses the interfacial charge recombination. This largely reduced the interfacial charge recombination loss and achieved a record efficiency of 21.1 % for n‐i‐p structured ETL‐free PSCs, outperforming their ETL‐containing metal oxide counterparts (18.7 %), as well as narrowing the efficiency gap with high‐efficiency PSCs employing highly crystalline TiO2 ETLs. [ABSTRACT FROM AUTHOR]

We, for the first time, correlated the alkyl chain length of amine molecules with the defect passivation efficacy, either on the surfaces or at grain boundaries of perovskite films. Blade-coated perovskite solar cells with long-chain amine passivation achieved an efficiency of 21.5%, accompanied by a small voltage loss of 0.35 V. [ABSTRACT FROM AUTHOR]

Multiple‐cation lead mixed‐halide perovskites (MLMPs) have been recognized as ideal candidates in perovskite solar cells in terms of high efficiency and stability due to decreased open‐circuit voltage loss and suppressed yellow phase formation. However, they still suffer from an unsatisfactory long‐term moisture stability. In this study, phosphorus‐containing Lewis acid and base molecules are employed to improve device efficiency and stability based on their multifunction including recombination reduction, phase segregation suppression, and moisture resistance. The strong fluorine‐containing Lewis acid treatment can achieve a champion PCE of 22.02%. Unencapsulated and encapsulated devices retain 63% and 80% of the initial efficiency after 14 days of aging under 75% and 85% relative humidity, respectively. The better passivation of Lewis acid implies more halide defects than Pb defects at the MLMP surface. This unbalanced defect type results from phase segregation that is the synergistic effect of Cs and halide ion migrations. Identifying defect type based on different passivation effects is beneficial to not only choose suitable passivators to boost the efficiency and slow down the moisture degradation of MLMP solar cells, but also to understand the mechanism of defect‐assisted moisture degradation. [ABSTRACT FROM AUTHOR]

Halide perovskite materials have achieved overwhelming success in various optoelectronic applications, especially perovskite solar cells and perovskite‐based light‐emitting diodes (P‐LEDs), owing to their outstanding optical and electric properties. It is widely believed that flat and mirror‐like perovskite films are imperative for achieving high device performance, while the potential of other perovskite morphologies, such as the emerging textured perovskite, is overlooked, which leaves plenty of room for further breakthroughs. Compared to flat and mirror‐like perovskites, textured perovskites with unique structures, e.g., coral‐like, maze‐like, column‐like or quasi‐core@shell assemblies, are more efficient at light harvesting and charge extraction, thus revolutionizing the pathways toward ultrahigh performance in perovskite‐based optoelectronic devices. Employing a textured perovskite morphology, the record of external quantum efficiency for P‐LEDs is demonstrated as 21.6%. In this research news, recent progress in the utilization of textured perovskite is summarized, with the emphasis on the preparation strategies and prominent optoelectronic properties. The impact of the textured morphology on light harvesting, carrier dynamic management, and device performance is highlighted. Finally, the challenges and great potential of employing these innovative morphologies in fabricating more efficient optoelectronic devices, or creating a new energy harvesting and conversion regime are also provided. [ABSTRACT FROM AUTHOR]

The power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) are already higher than those of other thin-film photovoltaic technologies, but the high-efficiency cells are based on complicated device architectures with multiple layers of coating. A promising strategy to commercialize this emerging technology is to simplify the device structure while simultaneously maintaining high-efficiency. Charge transport layers (CTLs) are generally indispensable for achieving high-performance PSCs, but the high cost and possibility of instability hinder the mass production of efficient, stable PSCs in a cost-effective manner. The ambipolar carrier transfer characteristic of perovskite materials makes it possible to fabricate efficient PSCs even in the absence of electron and/or hole transport layers. Encouragingly, the reported PCEs of CTL-free PSCs are already over 20%. However, it is still a mystery about why and how CTL-free devices can work efficiently. Here, we summarize the recent strategies developed to improve the performance of CTL-free PSCs, aiming at strengthening the comprehensive understanding of the fundamental carrier dynamics, heterojunction merits and device physics behind these mysteriously simple yet efficient devices. This review sheds light on identifying the limiting and determining factors in achieving high-efficiency CTL-free devices, and proposes some empirical charge transport models (e.g. p-type doping of perovskites for HTL-free PSCs, n-type doping of perovskites for ETL-free PSCs, constructing efficient p–n heterojunctions and/or homojunctions at one side/interface or employing perovskite single crystal-based lateral geometry for both HTL and ETL-free PSCs, etc.) that are useful to further improve device performance. In addition, an insightful perspective for the future design and commercial development of large-scale, efficient and stable optoelectronic devices by employing carbon electrodes is provided. [ABSTRACT FROM AUTHOR]

The present work demonstrates a facile one-step process to fabricate thin films of amorphous titania nanowires on transparent conducting oxide substrates via hydrolysis of potassium titanium oxide oxalate in an aqueous solution at 90 °C. The resultant titania nanowire thin films (that have not undergone further annealing) are efficient electron transport layers in CH 3 NH 3 PbI 3 perovskite solar cells, yielding full sun solar-to-electricity conversion efficiencies of up to 14.67% and a stabilized efficiency of 14.00% under AM 1.5G one sun illumination, comparable to high temperature sintered TiO 2 counterparts. The high photovoltaic performance is attributed to the porous nanowire network that facilitates perovskite infiltration, its unique 1D geometry and excellent surface coverage for efficient electron transport, as well as suppressed charge recombination between FTO and perovskite. [ABSTRACT FROM AUTHOR]

The recent surge in efficiency and progress of organohalide perovskite solar cells (PSCs) has been significant. The PSC performance is significantly influenced by nanostructuring as this varies the intrinsic optical, electrical, and electrochemical properties. Diverse TiO2 electron transport layers (ETLs) are solvothermally grown on the transparent conducting oxide substrate with different dimensionalities, 0D nanoparticles (TNP), 1D nanowires (TNW) to 2D nanosheets (TNS), by varying the organic solvent used. These layers feature enhanced optical transparency (≈2%-5% transmittance improvement compared to pristine fluorine doped tin oxide, FTO, glass) minimizing light absorption losses. PSCs constructed using 1D TNW or 2D TNS yield enhanced photovoltaic performance compared to the 0D TNP counterparts. This is a result of i) improved infiltration of the perovskite in the porous TNW or TNS network and ii) facilitated electron transport and charge extraction at the TNW/perovskite or TNS/perovskite interfaces, thus reduced interfacial recombination loss. Employing a bilayered ETL film consisting of a selfassembled TiO2 blocking layer and a subsequent TNW active layer, produces PSC devices with an efficiency exceeding 16%. This bilayered ETL film can simultaneously block the photogenerated holes and enhance electron extraction, therefore improving PSC performance. [ABSTRACT FROM AUTHOR]

To achieve high-performance perovskite solar cells, especially with mesoscopic cell structure, the design of the electron transport layer (ETL) is of paramount importance. Highly branched anatase TiO2 nanowires (ATNWs) with varied orientation are grown via a facile one-step hydrothermal process on a transparent conducting oxide substrate. These films show good coverage with optimization obtained by controlling the hydrothermal reaction time. A homogeneous methyl­ammonium lead iodide (CH3NH3PbI3) perovskite thin film is deposited onto these ATNW films forming a bilayer architecture comprising of a CH3NH3PbI3 sensitized ATNW bottom layer and a CH3NH3PbI3 capping layer. The formation, grain size, and uniformity of the perovskite crystals strongly depend on the degree of surface coverage and the thickness of the ATNW film. Solar cells constructed using the optimized ATNW thin films (220 nm in thickness) yield power conversion efficiencies up to 14.2% with a short-circuit photocurrent density of 20.32 mA cm−2, an open-circuit photovoltage of 993 mV, and a fill factor of 0.70. The dendritic ETL and additional perovskite capping layer efficiently capture light and thus exhibit a superior light harvesting efficiency. The ATNW film is an effective hole-blocking layer and efficient electron transport medium for excellent charge separation and collection within the cells. [ABSTRACT FROM AUTHOR]

A powerful full solution-based process was demonstrated to synthesize various vertically aligned TiO 2 wires/rods self-assembled arrays nanostructures on conductive substrates via a simple hydrothermal growth system. Demonstrated samples included a family of high-quality and high-crystallinity anatase nanowire arrays with smooth, hierarchical or hyperbranched architectures, thanks to oriented attachment and crystallization as well as a self-assembly growth mechanism. The proposed hyperbranched arrays, consisting of long TiO 2 nanowire trunks, short TiO 2 nanorod branches as well as tiny TiO 2 nanorod leaves (recall a tree with luxuriant foliage) and thus possessing a microscopic feature size, overcome typical shortages of insufficient dye adsorption for conventional 1D smooth nanowire arrays or prototype hierarchical nanowire arrays when applied to DSSC, which achieved for the first time similar dye uptakes ( i.e. 90.10 nmol cm −2 vs 88.62 nmol cm −2 ) as nanoparticle counterparts under the same thickness. Dye-sensitized solar cell fabricated with an ~8 μm long novel hyperbranched nanowire arrays photoelectrode yields an impressive power conversion efficiency (PCE) of 8.11%, which was much greater than that of anatase TiO 2 nanoparticle (20 nm in diameter) counterpart due to synergistic effects of high dye uptakes and superior broadband light scattering for improved light harvesting as well as fast charge transport for efficient charge collection for the former. [ABSTRACT FROM AUTHOR]

Light-harvesting and charge collection have attracted increasing attention in the domain of photovoltaic cells, and can be facilitated dramatically by appropriate design of a photonic nanostructure. However, the applicability of current light-harvesting photoanode materials with single component and/or morphology (such as, particles, spheres, wires, sheets) is still limited by drawbacks such as insufficient electron-hole separation and/or light-trapping. Herein, we introduce a universal method to prepare hierarchical assembly of macroporous material-nanowire coated homogenous or heterogeneous metal oxide composite electrodes (TiO2-TiO2, SnO2-TiO2, and Zn2SnO4-TiO2; homogenous refers to a material in which the nanowire and the macroporous material have the same composition, i.e. both are TiO2. Heterogeneous refers to a material in which the nanowires and the macroporous material have different compositions). The dye-sensitized solar cell based on a TiO2-macroporous material-TiO2-nanowire homogenous composition electrode shows an impressive conversion efficiency of 9.51 %, which is much higher than that of pure macroporous material-based photoelectrodes to date. [ABSTRACT FROM AUTHOR]

Sn‐based perovskites have emerged as one of the most promising environmentally‐friendly photovoltaic materials owing to their low toxicity and exceptional optoelectronic properties. Nonetheless, the low‐cost production and stable operation of Sn‐based perovskite solar cells (PSCs) are still largely limited by the costly hole transport materials and the under‐optimized interfaces between hole transport layer (HTL) and Sn perovskite layer. Here, we innovatively developed a chlorine radical chemical bridging (Cl‐RCB) strategy that enabled to remove the HTL and optimize the indium tin oxide (ITO)/perovskite heterointerface for constructing high‐performance Sn‐based PSCs with simplified structures. The key is to modify the commercially‐purchased ITO electrode with highly active chlorine radicals that could effectively mitigate the surface oxygen vacancies, alter the chemical constitutions, and favorably down‐shifted the work function of ITO surface to be close to the valence band of perovskites. As a result, the interfacial energy barrier has been largely reduced by 0.20 eV and the interfacial carrier dynamics have been optimized at the ITO/perovskite heterointerface. Encouragingly, the efficiency of HTL‐free Sn‐based PSCs has been enhanced from 6.79 % to 14.20 %, which is on par with the state‐of‐the‐art conventional HTL‐containing counterparts (normally >14 % efficiency) and representing the record performance for the Sn perovskite photovoltaics in the absence of HTL. Notably, the target device exhibited enhanced stability for up to 2000 h. The Cl‐RCB strategy is also versatile to be used in Pb‐based and mixed Sn−Pb HTL‐free PSCs, achieving efficiencies of 22.27 % and 21.13 %, respectively, all representing the advanced device performances for the carrier transport layer‐free PSCs with simplified device architectures. [ABSTRACT FROM AUTHOR]

Optoelectronic Devices: The Rise of Textured Perovskite Morphology: Revolutionizing the Pathway toward High-Performance Optoelectronic Devices (Adv. In article number 1902256, Wu-Qiang Wu, Lianzhou Wang, Dai-Bin Kuang, and co-workers provide a snapshot of the recent exciting progress in utilizing the emerging textured perovskite morphologies in perovskite-based optoelectronic devices. The textured perovskite exhibits more efficient light harvesting and effective carrier dynamics management than the prototype flat and dense counterpart, enabling ground-breaking record device performance and diverse potential applications. [Extracted from the article]

Recent years have witnessed an incredibly high fever in metal halide perovskite materials due to their promising applications in a wide range of optoelectronic applications. The morphologies and optoelectronic properties of the perovskite layers play critical roles in affecting the optoelectronic performances. This review summarizes the recent advances in the fabrication of a variety of perovskite morphologies and their promising progress achieved in different optoelectronic applications, including solar cells, light‐emitting diodes, photodetectors, lasers, photocatalysis, X‐ray detectors/imagers, and luminescent solar concentrators. Several blossoming representatives, including 0D perovskite quantum dots, 1D perovskite nanowires, 2D perovskite nanosheets/nanoplatelets, and 3D textured perovskite assemblies (i.e., cuboid‐like, inverse opal‐like, coral‐like, or maze‐like morphologies, etc.), are highlighted to demonstrate their fascinating properties and outstanding capabilities for efficient optoelectronic applications. Finally, a perspective on the remaining challenges and future directions of fabricating unique perovskite morphologies for next‐generation high‐performance optoelectronic devices is provided. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) without an electron transport layer (ETL) exhibit fascinating advantages such as simplified configuration, low cost, and facile fabrication process. However, the performance of ETL‐free PSCs has been hampered by severe charge carrier recombination induced either by current leakage (insufficient perovskite film coverage) or inferior charge extraction. Herein, an additive‐assisted morphological engineering strategy is used to construct an intriguing bilayer perovskite film featuring a dense bottom layer and a maze‐like top layer. Such maze‐like perovskite films enable the construction of ETL‐free PSCs with a PCE of 18.5% and negligible hysteresis, which can be attributed to the higher crystallinity and superior light‐harvesting capability of the resultant perovskite film, as well as facilitated hole extraction at the hole transport layer (HTL)/perovskite interface. This work provides a simple approach to modify the perovskite film morphology and demonstrates the correlation between facilitated charge‐carrier extraction and high‐performance ETL‐free perovskite photovoltaics. An intriguing maze‐like CH3NH3PbI3 film featuring a bilayer structure with a dense bottom layer and a porous top layer is judiciously designed for electron transport layer‐free perovskite solar cells (PSCs). Such maze‐like perovskite film shows high crystallinity, superior light‐harvesting capability, and enables facilitated hole extraction at the perovskite/hole transport layer interface, thus leading to a PCE of 18.5% with negligible hysteresis. [ABSTRACT FROM AUTHOR]

Microscopic design and morphological engineering of the semiconducting metal oxide as electron‐transporting layers (ETLs) is of vital importance for optical enhancement, photonic structuring, and charge collection optimization within optoelectronic devices. Herein, nanowire‐coated, branched macroporous titania (BMT) thin films are reported as a new type of ETL prepared by using silica spheres as a sacrificial template, followed by a sol–gel and subsequent alkaline‐assisted etching process. The BMT films feature 3D hierarchical structures and interconnected networks with tunable pore sizes, branch densities, and film thicknesses. The titania films are employed as ETLs in perovskite solar cells (PSCs), resulting in remarkable power conversion efficiencies (PCEs) of 20.1%; a noticeable 16% increase compared with titania nanowire (TNW) ETL‐based counterparts (PCE = 17.3%). The superior device performance of the BMT‐based PSCs can be attributed to the maximized light harvesting and charge collection capabilities. These beneficial properties are derived from the effective infiltration of the perovskite precursor into the titania macropores, efficient light confinement within the macropore structure, and the textured perovskite capping layer, as well as enhanced charge transport and reduced charge recombination through the BMT architecture. This work demonstrates a simple and effective approach for constructing branched macroporous metal‐oxide photoelectrodes toward high‐performance photovoltaic devices. A template‐assisted solution‐processed technique is developed to fabricate 3D nanowire‐coated macroporous titania thin films with outstanding optical and electrical properties. Perovskite solar cells based on newly prepared TiO2 electron‐transporting layer deliver an impressive power conversion efficiency of up to 20.1% owing to enhanced light harvesting and facilitated charge collection. [ABSTRACT FROM AUTHOR]

[Display omitted] Narrow-bandgap mixed Sn-Pb perovskite solar cells (PSCs) have showcased great potential to approach the Shockley-Queisser limit. Nevertheless, the practical application and long-term deployment of mixed Sn-Pb PSCs are still largely impeded by the rapid oxidation of Sn2+ ions and under-optimized carrier transport layer (CTL)/perovskite interfaces that would inevitably incur serious interfacial charge recombination and device performance degradation. Herein, we successfully removed the hole transport layer (HTL) by incorporating a small amount of organic phosphonic acid molecules into perovskites, which could preferably interact with Sn2+ ions (relative to Pb2+ analogues) at the grain boundaries (GBs) throughout the perovskite film thickness via coordination bonding, thus effectively retarding the oxidation of Sn2+, passivating the defects and suppressing the non-radiative recombination. Targeted modification effectively reinforced built-in potential by ∼100 mV, and favorably induced energy level cascade, thus accelerating spatial charge separation and facilitating the hole extraction from perovskite layer to underlying conductive electrodes even in the absence of HTL. Consequently, enhanced power conversion efficiencies up to 20.21% have been achieved, which is the record efficiency for the HTL-free mixed Sn-Pb PSCs, accompanied by a decent photovoltage of 0.87 V and improved long-term stability over 2400 h. [ABSTRACT FROM AUTHOR]

This review highlights the recent advances of employing the perovskite crystals redissolution strategy in perovskite photovoltaics, with particular emphasis on comparing different methodologies for synthesizing perovskites, elucidating the distinct solution chemistry, analyzing the cost advantages, as well as underlining the desirable thin-film superiority with improved quality and enhanced optoelectronic properties. [Display omitted] High-efficiency perovskite solar cells (PSCs) normally rely on costly, high purity (>99.99%), air-sensitive raw materials that vary batch-to-batch. The perovskite films and devices derived from conventional raw materials mixture method suffer from inferior reproducibility of optoelectronic properties and performance, as well as discounted promise towards low-cost scalable manufacturing. Distinguished from the direct mixing of raw materials, the preparation of perovskite films with precursors made by the redissolution of perovskite crystals holds the promise to make PSCs more affordable, reproducible, efficient and stable. The resultant perovskite films inherit the exceptional characteristics of the parent perovskite crystals, such as high crystallinity, high purity, accurate stoichiometric ratio, and low trap-state density, as well as good ambient and phase stability. Herein, we summarize recent progress on the employment of the perovskite crystals redissolution strategy for achieving low-cost, efficient perovskite-based solar-to-electricity conversion, which will help both popularize the redissolution strategy and reveal unprecedented advantages gained by its adoption. [ABSTRACT FROM AUTHOR]

[Display omitted] The power conversion efficiency for single-junction solar cells is limited by the Shockley-Quiesser limit. An effective approach to realize high efficiency is to develop multi-junction cells. These years have witnessed the rapid development of organic–inorganic perovskite solar cells. The excellent optoelectronic properties and tunable bandgaps of perovskite materials make them potential candidates for developing tandem solar cells, by combining with silicon, Cu(In,Ga)Se 2 and organic solar cells. In this review, we present the recent progress of perovskite-based tandem solar cells, including perovskite/silicon, perovskite/perovskite, perovskite/Cu(In,Ga)Se 2 , and perovskite/organic cells. Finally, the challenges and opportunities for perovskite-based tandem solar cells are discussed. [ABSTRACT FROM AUTHOR]