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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.

ispartof: ADVANCED FUNCTIONAL MATERIALS vol:32 issue:52 status: published

Perovskite photovoltaics have witnessed overwhelming success owing to their high power conversion efficiency, low voltage deficit, sensitive photoelectric response and good operational stability. However, solution-processed, polycrystalline perovskite films inevitably contain a high density of crystallographic defects, such as uncoordinated ions and dangling bonds at the surfaces and grain boundaries, which can result in charge recombination, thus causing energy loss and impaired device performance. These intrinsic imperfections can be remedied through a chemically induced intermarriage between halide perovskites of soft crystallographic nature and judiciously designed exotic ligand molecules. Utilizing rational molecular design of the component moieties, i.e., the core and tail functional groups, the ligand molecules can be endowed with both more comprehensive and salient advantages to further boost device performance, thus setting perovskite photovoltaics on course for a more prosperous future.In this Account, we present our narrative of designing a series of favorable ligand molecules with multifunctionalities in terms of crystal growth modulation, grains cross-linking, defect passivation, surface functionalization, phase stabilization, and moisture invasion inhibition of perovskite films and summarize the advances made in designing molecular level custom ligands that have progressively lifted the record performances of perovskite photovoltaics. We first identify the origins of imperfections in perovskites and their detrimental impacts on device efficiency and stability. We then review feasible rules for ligand design, including tuning the length of the linear or branched alkyl chain core, the substitution of one or more carbon atoms with O, P, S, or NH, and the number of functional groups (double, triple, quadruple, or even multiple ones), to design “all-in-one” ligands with ideal molecular structures and multifunctionalities. The chemical interactions between ligands and perovskites (e.g., coordination bond, ionic bond, hydrogen bond, electrostatic interaction and chelation, etc.) are discussed, aiming to elucidate their impact on the necessary trade-off between defect passivation efficacy and charge transport property in ligand-modified perovskite films, and establish a triangular structure–property–performance relationship for perovskite-based optoelectronic devices with ligands modulation and passivation. We also insightfully explore novel ligand management strategies in perovskite quantum dots, especially the development of ligand-assisted cation exchange and surface ligand density optimization. Finally, we present an astute perspective of future trends in the rational design of innovative ligand molecules with desired structures and properties for more efficient, stable, perovskite-based optoelectronic devices.

Simplified structures of perovskite solar cells can reduce the fabrication and materials cost while simultaneously achieving high efficiencies, which are highly attractive for practical industrial production.

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)Se2 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)Se2, and perovskite/organic cells. Finally, the challenges and opportunities for perovskite-based tandem solar cells are discussed.

In this work, the hollow rectangular prism-like TiO2 (HRP-TiO2) mesocrystals with exposed {001} facets were synthesized via an in-situ hydrothermal process without introducing any additional hydrof...

The suboptimal carrier dynamics at the perovskite/electron transport layer has largely limited the further performance enhancement of the state-of-the-art inverted p-i-n structured perovskite solar cells. Herein, we discovered that a simple surface modification of the perovskite film by a trivalent metal halide salt, InBr3, could convert the doping levels of the top surface to be more n-type, which spontaneously formed an intriguing n/n+ homojunction between the bulk (weak n type (n) component) and the surface (more n-type (n+) component) in a monolithic perovskite film. This brought about synergistic advantages of the enlarged built-in electric field for facilitated charge separation, as well as optimized electronic energy level alignment and minimized electron injection barrier at the perovskite/C60 interface, leading to both accelerated charge extraction and suppressed interfacial charge recombination. Blade-coated inverted PSCs with n/n+ homojunctions achieved a high power conversion efficiency (PCE) of up to 22.2%, narrowing the efficiency gap with their conventional n-i-p counterparts. The InBr3 surface treatment also improved the operational stability to >1000 hours under light with 93% initial efficiency retained.

Over the past decade, organic‐inorganic metal halide perovskites have attracted tremendous research interest owing to their prominent optical and electric properties. These fantastic perovskite materials have been widely employed in a variety of optoelectronic devices, such as perovskite solar cells (PSCs), light‐emitting diodes (LEDs), photocatalysts, photodetectors and X‐ray imaging.[1]

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 % forn-i-pstructured 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 TiO(2)ETLs.

Mapping perovskite trap states The high efficiency of hybrid inorganic-organic perovskite solar cells is mainly limited by defects that trap the charge carriers and lead to unproductive recombination. Ni et al. used drive-level capacitance profiling to map the spatial and energetic distribution of trap states in both polycrystalline and single-crystal perovskite solar cells. The interface trap densities were up to five orders of magnitude higher than the bulk trap densities. Deep traps were mainly located at the interface of perovskites and hole-transport layers, where processing created a high density of nanocrystals. These results should aid efforts aimed at avoiding trap-state formation or passivating such defects. Science , this issue p. 1352

The development of solution-processed inorganic amorphous electron-transporting layers (ETLs) is important for the future commercialization of perovskite solar cells (PSCs). The formation of such ETLs using low-temperature processing techniques will lower potential production costs and accommodate diverse substrate materials. Herein, a low-temperature (

Two phenazine copolymer donors P1 and P2 were developed. P1 and P2 have deep highest occupied molecular orbital levels, enhanced light-harvesting capability and good hole mobility. Solar cells based on P2 and a nonfullerene acceptor, Y6, gave a power conversion efficiency (PCE) of 15.14%, which has been the highest value achieved by phenazine-donor-based solar cells to date.

Organic small molecules like ammonium halide salts (AHSs) are widely used to suppress the non-radiative charge recombination of solution-processed halide perovskite films with defective surface and unfavorable energy levels for enhanced photovoltage, but more often than not at a cost of enlarging the band gap of perovskite materials, which limits the light absorption and thus, the photocurrent density. In addition, there is still a lack of fundamental understanding and visual characterization of the surface and bulk composition change upon subsequent surface treatment with heterogeneous ingredients. Herein, we report and identify that AHS soaking treatment enables the formation of δ-FAPbI3 on the surface of the perovskite film for defect passivation functions, thus reducing the interfacial recombination loss and increasing photovoltage. Meanwhile, the AHS molecules diffuse and alloy with the bulk perovskite material to reduce the band gap, red-shifting the absorption region and thus increasing the photocurrent. Blade-coated perovskite solar cells (PSCs) prepared via AHS treatment achieved a champion power conversion efficiency (PCE) of 21.9% with a high open-circuit voltage (Voc) up to 1.18 V under AM 1.5G sun illumination, which is remarkably higher than the pristine PSCs without any treatment (19.2%), and outperforms other blade-coated PSCs, regardless of their perovskite compositions. Surface treatment of perovskite films with functional, organic small molecules is a promising strategy for rational composition management and favorable gradient distribution, which are beneficial for realizing efficient and stable PSCs.

Primary amines function well in defect passivation, crystal modulation, and surface functionalization in perovskite solar cells and perovskite light-emitting diodes, yielding record performances.

Recent years have witnessed an explosive interest in branched TiO2 nanostructures (BTNs) due to their promising applications in a wide range of energy-related fields. As anode materials for solar cells (dye- or quantum dot-sensitized solar cells and perovskite solar cells), photoelectrochemical synthetic cells and energy storage devices (e.g., Li-ion batteries), BTNs with inherent nature of structural hierarchy and porosity, provide fascinating optical, electrical and electrochemical properties such as high surface area, superior light scattering and confinement, and fast electron transport. This review summarizes the recent advances in the preparation of BTNs with tailored host-guest morphologies, branches compositions and structural complexity. Their promising progress achieved in the field of energy conversion and storage is discussed. Two blossoming representatives, including the tree-like branched TiO2 nanoarrays and urchin-like branched TiO2 spheres, are highlighted to shed light on the effect of smart surface branched modification on improving the solar-to-electricity or solar-to-fuel conversion efficiencies, and increasing energy (power) densities. In addition, we also provide perspective on the new trend and future directions of novel multifunctional BTNs for next-generation energy conversion and storage devices.

Suppressed charge recombination and facilitated charge collection are critical for achieving perovskite solar cells (PSCs) with improved efficiency and stability. Herein, a multifunctional 2D polymeric semiconductor is incorporated into perovskite ink to assist the crystal growth of perovskite films with large grains and fewer defects. Anchoring heterogeneous polymeric molecules on perovskite not only enhances the efficacy of defect passivation at the grain boundaries and/or surface but also facilitates the charge extraction and collection, as evidenced by thermal admittance spectroscopy and femtosecond transient absorption spectroscopy. Accordingly, the PSCs incorporated with a polymeric semiconductor achieve power conversion efficiencies (PCEs) up to 21.1% (aperture 0.16 cm2) and 19.5% (aperture 1.0 cm2), featuring an illustrious open-circuit voltage of 1.16 V (corresponding to a small voltage loss of 0.39 V) and an improved device operational stability (∼90% initial efficiency retained after constant one sun illumination for 500 h). This work highlights the effectiveness of using multifunctional passivation agents capable of providing surprisingly robust efficacy in defect passivation of perovskite, which are also advantageous to crystal growth modulation and carrier dynamic management for efficient and stable PSCs.

A high-performance optoelectronic device requires efficient light harvesting and management in the electrodes. In this work, we report the integration of antireflective anatase TiO2 nanowire (TNW) arrays and CH3NH3PbI3 microcuboid (CMC) film into a new bilayer architecture. The highly porous and well-interconnected anatase TNW arrays showcase antireflective properties for enhanced light transmittance and provide a largely accessible surface area for anchoring the perovskite light absorber. The thick and compact CMC film enables efficient light absorption. Thus, perovskite solar cells (PSCs) fabricated with a hybrid TNW/CMC optoelectronic electrode achieved an optimal power conversion efficiency (PCE) of up to 20.1% under one sun illumination with a high Jsc of 23.2 mA cm−2, which can be attributed to the maximised light harvesting efficiency within the devices.

Perovskite solar cells (PSCs) have witnessed an overwhelming success in their skyrocketed power conversion efficiencies (PCEs) within a short period, but a fully solution-processed fabrication of PSC multilayer stack has not been achieved. Herein, we report to fabricate the simplified PSCs with perovskite layer sandwiched and encapsulated between carbon-based electron transport layer (ETL) and counter electrode (CE) via 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 induced by perovskite precursor. The AS serves as a“molecular glue”to strengthen the adhesion toughness at the TCO/ETL interface via robust chemical interaction and bonding, which remarkably facilitates the interfacial charge extraction, increases the PCEs by 77% and reduces the hysteresis. A champion PCE of 18.64% has been achieved for the fully-printed devices, which is one of the highest reported values for the carbon-based PSCs. AS-assisted interfacial linkage and carbon materials-assisted self-encapsulation remakably enhance the stability of the resultant PSCs, which did not experience any performance degradation when stored at ambient conditions for more than 3000 hours. This work provides a novel strategy to tackle the incompatibility issue of depositing each functional layer by using a full solution process and offers an additional promise of constructing efficient perovskite-based optoelectronics with prolonged lifespan in a low-cost manner.

The development of solution-processed inorganic amorphous electron-transporting layers (ETLs) is important for the future commercialization of perovskite solar cells (PSCs). The formation of such ETLs using low-temperature processing techniques will lower potential production costs and accommodate diverse substrate materials. Herein, a low-temperature (150 °C) solution process forms amorphous titania nanowire (Am-TNW) thin films on fluorine-doped tin oxide conducting glass substrates. When applied as an ETL in PSCs, the Am-TNW layer achieves a higher average power conversion efficiency (18.3%) relative to that of a nanocrystalline anatase TNW (ATNW) layer obtained after high-temperature (500 °C) heating (16.7%). Compared to the ATNW counterparts, the Am-TNW-based PSCs exhibit inferior charge extraction across the TNW/CH

State-of-the-art, high-performance perovskite solar cells (PSCs) contain a large amount of iodine to realize smaller bandgaps. However, the presence of numerous iodine vacancies at the surface of the film formed by their evaporation during the thermal annealing process has been broadly shown to induce deep-level defects, incur nonradiative charge recombination, and induce photocurrent hysteresis, all of which limit the efficiency and stability of PSCs. In this work, modifying the defective surface of perovskite films with cadmium iodide (CdI2) effectively reduces the degree of surface iodine deficiency and stabilizes iodine ions via the formation of strong Cd-I ionic bonds. This largely reduces the interfacial charge recombination loss, yielding a high efficiency of 21.9% for blade-coated PSCs with an open-circuit voltage of 1.20 V, corresponding to a record small voltage deficit of 0.31 V. The CdI2 surface treatment also improves the operational stability of the PSCs, retaining 92% efficiency after constant illumination at 1 sun intensity for 1000 h. This work provides a promising strategy to optimize the surface/interface optoelectronic properties of perovskites for more efficient and stable solar cells and other optoelectronic devices.

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.

Nanostructured TiO2 with differentiate morphologies has attracted tremendous attention due to its wide band-gap nature as well as outstanding optical and electric properties for solar-driven light-to-electricity conversion application. Layered-stacking TiO2 film such as double-layer, tri-layer, quadruple- or quintuplicate-layer, is highly desirable to the design of high-performance semiconductor material photoanodes and the development of advanced photovoltaic devices. In this minireview, we will summarize the recent progress and achievements on proof-of-concept of layered-stacking TiO2 films (LTFs) for solar cells with emphasis on the tailored properties and synergistic functionalization of LTFs, such as optimized sensitizer adsorption, broadened light confinement as well as facilitated electron transport characteristics. Various demonstrations of LTFs photovoltaic systems provide lots of possibilities and flexibilities for more efficient solar energy utilization that a wide variety of TiO2 with distinguished morphologies can be integrated into differently structured photoanodes with synergistic and complementary advantages. This key structure engineering technology will also pave the way for the development of next generation state-of-the-art electronics and optoelectronics. Finally, from our point of view, we conclude the future research interest and efforts for constructing more efficient LTFs as photoelectrode, which will be highly warranted to advance the solar energy conversion process.

The development of ternary metal oxide based electron transporting layers (ETLs) opens an alternative composition for constructing perovskite solar cells (PSCs). Herein, a solution processed route to prepare a dense and uniform ZnSnO (ZTO) thin film is reported for use as an excellent alternative ETL material for high-performance planar PSCs. The ZTO film exhibits good antireflective properties, with significantly improved optical transmittance over the entire range of wavelengths. The ZTO ETL improves the quality of the methylammonium lead iodide (MAPbI) layer, giving enhanced crystallinity and a flatter surface. The hole-blocking ability, suitable energy band positioning for MAPbI and high electron mobility of the ZTO films facilitate the charge extraction and collection at the ZTO/MAPbI interface and suppress the charge recombination through the planar PSC device. The best-performing PSC based on the optimized ZTO ETL thin film exhibits a champion power conversion efficiency of 16.38% under AM 1.5G one sun illumination (100 mW cm), indicating that ZTO is a promising ETL alternative for the construction of highly efficient perovskite photovoltaic devices. These ETL thin films have good optical and electrical properties, such as antireflection for maximized light harvesting as well as high electron mobility and interfacial band-alignment for charge collection.

The deposition of dense and uniform perovskite films with large grains is crucial for fabricating high-performance perovskite solar cells (PSCs). High-quality CH3NH3PbI3 films were produced by a self-induced intragranular-coarsening approach. The perovskite precursor solution contained a Lewis base, N,N-dimethyl sulfoxide (DMSO), and was deposited using a gas-assisted, one-step, spin-coating method that was followed by a solvent vapor-assisted annealing treatment using a mix of DMSO and chlorobenzene (CBZ). Combining solvent-engineering with gas-assisted deposition helps to form intermediate crystalline entities upon evaporation of the parent solvent but retards the otherwise fast reaction between the precursor ingredients. Subsequent cosolvent annealing induces further grain-coarsening via a facilitated dissolution–precipitation process. This technique produced flat CH3NH3PbI3 films featuring large grain microstructures, with well-coarsened subgrains and a reduction of intragranular defects that minimize...

To achieve high-performing perovskite solar cells (PSCs) interfacial engineering of the perovskite thin film and charge carrier-selective layers is vital for fast extraction of photogenerated electrons and holes, and the suppression of electron-hole recombination. Herein, a glucose-assisted self-assembly solvothermal protocol is reported to prepare electron-rich TiO2 thin films as effective electron transport layers exhibiting enhanced electron mobility. Bilayer structured CH3NH3PbI3 perovskite films are spontaneously formed, consisting of a flat and dense bottom layer forming the TiO2/CH3NH3PbI3 planar heterojunction and a textured and porous top layer elongating in the vertical direction forming the CH3NH3PbI3/spiroMeOTAD bulk heterojunction. The integrated planar and bulk dual heterojunction based PSCs are efficient in light harvesting and charge collection, and thus yield power conversion efficiencies up to 17.75% and a stabilized power output above 17.20%. Integrating both planar and bulk heterojunctions into a PSC assembly provides an effective approach for fabricating highly efficient perovskite optoelectronic devices.

To fabricate an effective antibacterial coating on the surfaces of diverse sanitary ceramic utensils, efficient titania photocatalysts with integrated features including high temperature anatase phase stability (>800 °C), excellent particle mobility for the formation of uniform thin coatings, high crystallinity and narrow particle size distribution are desirable. In this study, monodisperse dopant-free titania microspheres were synthesized with large pore size (∼80 nm) that remain anatase even after calcination at 900 °C. These titania microspheres were fabricated via a facile solvothermal treatment of amorphous spheres in the presence of 4.5 wt% ammonia solution and consisted of well-crystallized and faceted anatase nanocrystals with a uniform size of 24 nm. The anatase nanocrystals with high crystallinity and narrow crystal size distribution are responsible for their high temperature stability. The resulting anatase titania microspheres exhibited enhanced photocatalytic performance even after calcination at high temperature due to the retention of the anatase phase and the enhanced crystallinity. Such monodisperse anatase microspheres have potential to be applied as smart coating materials for antibacterial and self-cleaning applications.

Over the past several years, thin film organic–inorganic halide perovskite solar cells (PSCs) have rapidly improved with their power conversion efficiency (PCE) reaching over 22%, nearing that of polycrystalline silicon solar cells. This emerging photovoltaic technology has shown great potential for large-scale application owing to its high efficiency, low material cost and facile fabrication process. Electron-selective contacts, n-type materials that favor the charge transport and collection from the perovskite light absorbers to the front electrode, are important and seen as critical to fabricate high-performance PSCs. In this review, recent progress in such n-type materials is overviewed, with the emphasis on the most explored inorganic semiconducting metal oxides (including TiO2, SnO2, ZnO and Zn2SnO4). The impact of the structure of the n-type materials on the morphology of the perovskite films, the charge extraction and recombination, as well as device performance is highlighted. Optimization of n-type materials and their application in different device architectures are also summarized. An understanding of the intricate function of the n-type materials in PSC devices will assist in the design of materials to give precise control over the light harvesting and charge collection within PSC devices leading to high-performance.

Hierarchical metal oxide nanotree array architectures with tunable three-dimensional (3D) morphologies and homo-/heterogeneous junctions, consisting of 1D/2D nanobranches grown epitaxially on the sidewalls of vertical 1D nanostructured trunks (resembling a tree), have been widely explored to demonstrate their huge potential in the development of high-performance photovoltaic devices. In this review, the growth of a wide variety of TiO2 nanotree array architectures will be discussed, with an emphasis on solution-phase and vapor-phase syntheses. The evolution of electrode materials and recent progress in 3D TiO2 nanotree array architectures for solar cells are reviewed. Furthermore, to highlight the obvious benefits of 3D TiO2 nanotree arrays, the limitations and challenges of these hierarchical array architectures when used in solar cells are addressed. Finally, insight into future directions and opportunities for these fascinating electrode materials in creating a new energy conversion epoch is also provided.

Improved photovoltaic performance is reported for perovskite solar cells (PSCs) based on three-dimensional (3D) titanium oxide nanoarray electron transporting layers (ETLs). A solution-process is used to fabricate 3D nanoarrays that consist of rutile TiO2 nanorods (RTNR) with optimal lengths of 600 nm and an outside layer made of rutile, anatase or amorphous TiO2 nano-branches (referred to as RTB, ATB and Am-TB, respectively). These nanoarrays benefit perovskite precursor infiltration and increase the interfacial contact between the perovskite layer and ETL for efficient charge extraction. The PSCs based on the RTNR@ATB or RTNR@Am-TB arrays exhibit enhanced performance with improved open-circuit voltage (Voc) and fill factor (FF), compared to the RTNR@RTB or pristine RTNR counterparts. This is assigned primarily to the appropriate band alignment between the nanorods and nano-branches forming a favorable charge extraction ‘energy cascade’, and to a beneficial surface passivation effect limiting charge recombination. PSCs (with minimal hysteresis) achieved 16.06% efficiency when the rutile trunks were modified with surface amorphous nano-branches, with a short-circuit photocurrent density (Jsc) of 21.80 mA cm−2, Voc of 1010 mV and FF of 0.73. This unique morphological design provides an approach for constructing novel 3D electrodes for the fabrication of optoelectronic devices.

We compare three representative high performance PV materials: halide perovskite MAPbI3, CdTe, and GaAs, in terms of photoluminescence (PL) efficiency, PL lineshape, carrier diffusion, and surface recombination and passivation, over multiple orders of photo-excitation density or carrier density appropriate for different applications. An analytic model is used to describe the excitation density dependence of PL intensity and extract the internal PL efficiency and multiple pertinent recombination parameters. A PL imaging technique is used to obtain carrier diffusion length without using a PL quencher, thus, free of unintended influence beyond pure diffusion. Our results show that perovskite samples tend to exhibit lower Shockley–Read–Hall (SRH) recombination rate in both bulk and surface, thus higher PL efficiency than the inorganic counterparts, particularly under low excitation density, even with no or preliminary surface passivation. PL lineshape and diffusion analysis indicate that there is considerable structural disordering in the perovskite materials, and thus photo-generated carriers are not in global thermal equilibrium, which in turn suppresses the nonradiative recombination. This study suggests that relatively low point-defect density, less detrimental surface recombination, and moderate structural disordering contribute to the high PV efficiency in the perovskite. This comparative photovoltaics study provides more insights into the fundamental material science and the search for optimal device designs by learning from different technologies.

Ordered 1D metal oxide structure is desirable in thin film solar cells owing to its excellent charge collection capability. However, the electron transfer in 1D electron transporting layer (ETL)-based devices is still limited to a submicrometer-long pathway that is vertical to the substrate. Here, an innovative closely packed rutile TiO nanowire (CRTNW) network parallel to the facet of fluorine-doped tin oxide (FTO) substrate is reported, which can serve as a 1D nanoscale electron transport pathway for efficient perovskite solar cells (PSCs). The PSC constructed using newly prepared CRTNW ETL achieves an impressive power conversion efficiency of 21.10%, which can be attributed to the facilitated electron extraction induced by the favorable junctions formed at FTO/ETL and ETL/perovskite interfaces and also the suppressed charge recombination originating from improved perovskite morphology with large grains, flat surface, and good surface coverage. The bifacial contact junctions engineering also enables large-area device fabrication. The PSC with 1 cm aperture yields an efficiency of 19.50% under one sun illumination. This work highlights the significance of controlling the orientation and packing density of the ordered 1D oxide nanostructured thin films for highly efficient optoelectronic devices in a large-scale manner.

ConspectusThe utilization of solar energy and the development of its related optoelectronic devices have become more important than ever. Solar cells or photoelectrochemical (PEC) cells that require the design of light harvesting assemblies for efficiently converting solar light into electricity or solar fuels are of particular interest. Semiconductor TiO2, serving as the photoelectrode for photovoltaic devices (e.g., dye- or quantum dot-sensitized solar cells (DSSCs/QDSSCs) or perovskite solar cells (PSCs)) and PEC cells, has aroused intense research interest owing to its inherent characteristics of wide band gap and promising optical and electrical properties.TiO2 nanowires (TNWs) have been widely used in optoelectronic devices due to their unique 1D geometry and salient optical and electrical properties. However, the insufficient surface area resulting from the relatively large diameter of NWs and considerable free space between adjacent NWs restricts their optoelectronic performance. Hence, it is desi...

Anchoring monolayer bilateral amines on perovskite passivates surface defects, reinforces grain boundaries, and enhances stability., The power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) are already higher than that of other thin film technologies, but laboratory cell-fabrication methods are not scalable. Here, we report an additive strategy to enhance the efficiency and stability of PSCs made by scalable blading. Blade-coated PSCs incorporating bilateral alkylamine (BAA) additives achieve PCEs of 21.5 (aperture, 0.08 cm2) and 20.0% (aperture, 1.1 cm2), with a record-small open-circuit voltage deficit of 0.35 V under AM1.5G illumination. The stabilized PCE reaches 22.6% under 0.3 sun. Anchoring monolayer bilateral amino groups passivates the defects at the perovskite surface and enhances perovskite stability by exposing the linking hydrophobic alkyl chain. Grain boundaries are reinforced by BAA and are more resistant to mechanical bending and electron beam damage. BAA improves the device shelf lifetime to >1000 hours and operation stability to >500 hours under light, with 90% of the initial efficiency retained.

Perovskite solar cells (PSCs) have been rapidly crowded into the emerging photovoltaic technology, exhibiting continuously boosted power conversion efficiencies (PCEs) over 25%. Despite the high PCE, the voltage loss (Vloss) of PSCs still need to be further reduced to achieve higher open-circuit voltage (Voc) and thus approaching its Shockley–Queisser limit. Great effort on minimizing the Vloss has been made by mainly suppressing non-radiative recombination in perovskite and/or relevant interface, maximizing initial radiative efficiency, and modifying energy level alignment in PSCs. However, a timely overview of the lowest Vloss values achieved and the strategies of suppressing Vloss for the PSCs based on the most prevalent perovskite compositions is still lacking. In this review, the definition and determining factors of Vloss are elucidated, and the state-of-the-art low Vloss values of PSCs based on various types of prevailing perovskites with variable bandgaps are comprehensively discussed. The strategies for suppressing Vloss of PSCs are highlighted, aiming to boost the fundamental understanding of related Vloss mechanisms. Finally, an insightful perspective on further suppressing the Vloss in PSCs is provided, targeting on achieving new record PCEs in PSCs.