Interface Engineering for All‐Inorganic CsPbI2Br Perovskite Solar Cells with Efficiency over 14%

In this work, a SnO₂/ZnO bilayered electron transporting layer (ETL) aimed to achieve low energy loss and large open‐circuit voltage (V_oc) for high‐efficiency all‐inorganic CsPbI₂Br perovskite solar cells (PVSCs) is introduced. The high‐quality CsPbI₂Br film with regular crystal grains and full coverage can be realized on the SnO₂/ZnO surface. The higher‐lying conduction band minimum of ZnO facilitates desirable cascade energy level alignment between the perovskite and SnO₂/ZnO bilayered ETL with superior electron extraction capability, resulting in a suppressed interfacial trap‐assisted recombination with lower charge recombination rate and greater charge extraction efficiency. The as‐optimized all‐inorganic PVSC delivers a high V_oc of 1.23 V and power conversion efficiency (PCE) of 14.6%, which is one of the best efficiencies reported for the Cs‐based all‐inorganic PVSCs to date. More importantly, decent thermal stability with only 20% PCE loss is demonstrated for the SnO₂/ZnO‐based CsPbI₂Br PVSCs after being heated at 85 °C for 300 h. These findings provide important interface design insights that will be crucial to further improve the efficiency of all‐inorganic PVSCs in the future.     

Low‐Temperature In Situ Amino Functionalization of TiO2 Nanoparticles Sharpens Electron Management Achieving over 21% Efficient Planar Perovskite Solar Cells

Titanium oxide (TiO₂) has been commonly used as an electron transport layer (ETL) of regular‐structure perovskite solar cells (PSCs), and so far the reported PSC devices with power conversion efficiencies (PCEs) over 21% are mostly based on mesoporous structures containing an indispensable mesoporous TiO₂ layer. However, a high temperature annealing (over 450 °C) treatment is mandatory, which is incompatible with low‐cost fabrication and flexible devices. Herein, a facile one‐step, low‐temperature, nonhydrolytic approach to in situ synthesizing amino‐functionalized TiO₂ nanoparticles (abbreviated as NH₂‐TiO₂ NPs) is developed by chemical bonding of amino (‐NH₂) groups, via Ti? N bonds, onto the surface of TiO₂ NPs. NH₂‐TiO₂ NPs are then incorporated as an efficient ETL in n‐i‐p planar heterojunction (PHJ) PSCs, affording PCE over 21%. Cs_0.05FA_0.83MA_0.12PbI_2.55Br_0.45 (abbreviated as CsFAMA) PHJ PSC devices based on NH₂‐TiO₂ ETL exhibit the best PCE of 21.33%, which is significantly higher than that of the devices based on the pristine TiO₂ ETL (19.82%) and is close to the record PCE for devices with similar structures and fabrication procedures. Besides, due to the passivation of the surface trap states of perovskite film, the hysteresis of current–voltage response is significantly suppressed, and the ambient stability of devices is improved upon amino functionalization.     

A 0D/3D Heterostructured All‐Inorganic Halide Perovskite Solar Cell with High Performance and Enhanced Phase Stability

Although organic–inorganic hybrid perovskite solar cells (PVSCs) have achieved dramatic improvement in device efficiency, their long‐term stability remains a major concern prior to commercialization. To address this issue, extensive research efforts are dedicated to exploiting all‐inorganic PVSCs by using cesium (Cs)‐based perovskite materials, such as α‐CsPbI₃. However, the black‐phase CsPbI₃ (cubic α‐CsPbI₃ and orthorhombic γ‐CsPbI₃ phases) is not stable at room temperature, and it tends to convert to the nonperovskite δ‐CsPbI₃ phase. Here, a simple yet effective approach is described to prepare stable black‐phase CsPbI₃ by forming a heterostructure comprising 0D Cs₄PbI₆ and γ‐CsPbI₃ through tuning the stoichiometry of the precursors between CsI and PbI. Such heterostructure is manifested to enable the realization of a stable all‐inorganic PVSC with a high power conversion efficiency of 16.39%. This work provides a new perspective for developing high‐performance and stable all‐inorganic PVSCs.     

Picosecond Capture of Photoexcited Electrons Improves Photovoltaic Conversion in MAPbI3:C70‐Doped Planar and Mesoporous Solar Cells

In this work, solar cells based on methylammonium lead iodide (MAPbI₃) doped in solution with C₇₀ fullerene in a mesoporous as well as planar electron‐transporting layer (ETL)‐free architecture are realized, showcasing in the latter case a record efficiency of 15.7% and an improved open‐circuit voltage (V_OC). Contrary to the bulk heterojunction previously reported, the C₇₀ molecules do not phase segregate and they are rather finely dispersed in the perovskite film, possibly infiltrating at the grain boundaries, while assisting the growth of a highly uniform perovskite layer. By means of time‐resolved femtosecond‐to‐nanosecond optical spectroscopy, with an extended spectral coverage, it is observed that electrons photogenerated in the perovskite are transferred to C₇₀ with a time constant of 20 ps. Despite being captured by C₇₀, electrons are not deeply trapped and can potentially bounce back into the perovskite, as suggested by the high fill factor and enhanced V_OC of the MAPbI₃:C₇₀ solar cells, especially in the case of the ETL‐free device configuration.     

Efficient Bifacial Passivation with Crosslinked Thioctic Acid for High-Performance Methylammonium Lead Iodide Perovskite Solar Cells

Defects, inevitably produced within bulk and at perovskite-transport layer interfaces (PTLIs), are detrimental to power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). It is demonstrated that a crosslinkable organic small molecule thioctic acid (TA), which can simultaneously be chemically anchored to the surface of TiO₂ and methylammonium lead iodide (MAPbI₃) through coordination effects and then in situ crosslinked to form a robust continuous polymer (Poly(TA)) network after thermal treatment, can be introduced into PSCs as a new bifacial passivation agent for greatly passivating the defects. It is also discovered that Poly(TA) can additionally enhance the charge extraction efficiency and the water-resisting and light-resisting abilities of perovskite film. These newly discovered features of Poly(TA) make PSCs herein achieve among the best PCE of 20.4% ever reported for MAPbI₃ with negligible hysteresis, along with much enhanced ultraviolet, air, and operational stabilities. Density functional theory calculations reveal that the passivation of MAPbI₃ bulk and PTLIs by Poly(TA) occurs through the interaction of functional groups ( COOH,  C S) in Poly(TA) with under-coordinated Pb²⁺ in MAPbI₃ and Ti⁴⁺ in TiO₂, which is supported by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.     

Stratified Oxygen Vacancies Enhance the Performance of Mesoporous TiO2 Electron Transport Layer in Printable Perovskite Solar Cells

The low electrical conductivity and the high surface defect density of the TiO₂ electron transport layer (ETL) limit the power conversion efficiency (PCE) of corresponding perovskite solar cells (PSCs). Here, the conductivity and defect modulation of the mesoporous TiO₂ (mp-TiO₂) ETL via oxygen vacancy (OV) management by the reduction and oxidation treatment are reported. Reduction treatment via reducing agent introduces abundant OVs into the TiO₂ nanocrystalline particles on the surface and at the subsurface. The following oxidation treatment via hydrogen peroxide removes the surface OVs while remains the subsurface OVs, resulting in stratified OVs. The stratified OVs improve the conductivity of TiO₂ ETL by increasing carrier donors and decrease nonradiative centers by reducing surface defects. Such synergy ensures the capability of mp-TiO₂ as the well-performed ETL with improved energy level alignment, suppressed interface recombination, enhanced carrier extraction, and transport. As a result, printable hole-conductor-free carbon-based mesoscopic PSCs based on the modulated mp-TiO₂ ETL demonstrate a highest reported PCE of 18.96%.     

Strategically Constructed Bilayer Tin (IV) Oxide as Electron Transport Layer Boosts Performance and Reduces Hysteresis in Perovskite Solar Cells

Nanostructured tin (IV) oxide (SnO₂) is emerging as an ideal inorganic electron transport layer in n–i–p perovskite devices, due to superior electronic and low‐temperature processing properties. However, significant differences in current–voltage performance and hysteresis phenomena arise as a result of the chosen fabrication technique. This indicates enormous scope to optimize the electron transport layer (ETL), however, to date the understanding of the origin of these phenomena is lacking. Reported here is a first comparison of two common SnO₂ ETLs with contrasting performance and hysteresis phenomena, with an experimental strategy to combine the beneficial properties in a bilayer ETL architecture. In doing so, this is demonstrated to eliminate room‐temperature hysteresis while simultaneously attaining impressive power conversion efficiency (PCE) greater than 20%. This approach highlights a new way to design custom ETLs using functional thin‐film coatings of nanomaterials with optimized characteristics for stable, efficient, perovskite solar cells.     

Interfacial Passivation of the p‐Doped Hole‐Transporting Layer Using General Insulating Polymers for High‐Performance Inverted Perovskite Solar Cells

Organic–inorganic lead halide perovskite solar cells (PVSCs), as a competing technology with traditional inorganic solar cells, have now realized a high power conversion efficiency (PCE) of 22.1%. In PVSCs, interfacial carrier recombination is one of the dominant energy‐loss mechanisms, which also results in the simultaneous loss of potential efficiency. In this work, for planar inverted PVSCs, the carrier recombination is dominated by the dopant concentration in the p‐doped hole transport layers (HTLs), since the F4‐TCNQ dopant induces more charge traps and electronic transmission channels, thus leading to a decrease in open‐circuit voltages (V_OC). This issue is efficiently overcome by inserting a thin insulating polymer layer (poly(methyl methacrylate) or polystyrene) as a passivation layer with an appropriate thickness, which allows for increases in the V_OC without significantly sacrificing the fill factor. It is believed that the passivation layer attributes to the passivation of interfacial recombination and the suppression of current leakage at the perovskite/HTL interface. By manipulating this interfacial passivation technique, a high PCE of 20.3% is achieved without hysteresis. Consequently, this versatile interfacial passivation methodology is highly useful for further improving the performance of planar inverted PVSCs.     

高效无机CsPbI2Br钙钛矿太阳能电池表面钝化的简便方法

近年来,基于CsPbI2Br的钙钛矿太阳能电池(PVSC)由于能在效率和稳定性之间获得良好平衡而受到越来越多的关注.通过溶液法制备的CsPbI2Br钙钛矿薄膜通常包含各种缺陷,为了获得具有高性能和良好稳定性的钙钛矿太阳能电池,这些缺陷需要被钝化.针对此问题,本文报道了一种简便的缺陷钝化策略,即通过在CsPbI2Br钙钛矿表面旋涂KF溶液来对其进行缺陷钝化.结果表明,沉积的KF大部分位于钙钛矿表面的晶界处,而钙钛矿膜的降解通常始于晶界,因此钝化后的PVSC具有更高的稳定性.稳态和时间分辨光致发光光谱均表明钙钛矿的缺陷被KF显著钝化了.最终,基于KF处理的CsPbI2Br的电池器件能量转换效率(PCE)提高到了15.01%,同时具有较大的开路电压(VOC,1.26 V).与之相比,基于CsPbI2Br的对照器件的PCE仅为14.14%,VOC只有1.18 V.     

Thermally Stable MAPbI3 Perovskite Solar Cells with Efficiency of 19.19% and Area over 1 cm2 achieved by Additive Engineering

Solution‐processed perovskite (PSC) solar cells have achieved extremely high power conversion efficiencies (PCEs) over 20%, but practical application of this photovoltaic technology requires further advancements on both long‐term stability and large‐area device demonstration. Here, an additive‐engineering strategy is developed to realize a facile and convenient fabrication method of large‐area uniform perovskite films composed of large crystal size and low density of defects. The high crystalline quality of the perovskite is found to simultaneously enhance the PCE and the durability of PSCs. By using the simple and widely used methylammonium lead iodide (MAPbI₃), a certified PCE of 19.19% is achieved for devices with an aperture area of 1.025 cm², and the high‐performing devices can sustain over 80% of the initial PCE after 500 h of thermal aging at 85 °C, which are among the best results of MAPbI₃‐based PSCs so far.     

Highly Efficient and Stable Flexible Perovskite Solar Cells with Metal Oxides Nanoparticle Charge Extraction Layers

In this study, the fabrication of highly efficient and durable flexible inverted perovskite solar cells (PSCs) is reported. Presynthesized, solution‐derived NiO_x and ZnO nanoparticles films are employed at room temperature as a hole transport layer (HTL) and electron transport layer (ETL), respectively. The triple cation perovskite films are produced in a single step and for the sake of comparison, ultrasmooth and pinhole‐free absorbing layers are also fabricated using MAPbI₃ perovskite. The triple cation perovskite cells exhibit champion power conversion efficiencies (PCEs) of 18.6% with high stabilized power conversion efficiency of 17.7% on rigid glass/indium tin oxide (ITO) substrates (comparing with 16.6% PCE with 16.1% stabilized output efficiency for the flexible polyethylene naphthalate (PEN)/thin film barrier/ITO substrates). More interestingly, the durability of flexible PSC under simulation of operative condition is proved. Over 85% of the maximum stabilized output efficiency is retained after 1000 h aging employing a thin MAPbI₃ perovskite (over 90% after 500 h with a thick triple cation perovskite). This result is comparable to a similar state of the art rigid PSC and represents a breakthrough in the stability of flexible PSC using ETLs and HTLs compatible with roll to roll production speed, thanks to their room temperature processing.     

Graded Heterojunction Engineering for Hole‐Conductor‐Free Perovskite Solar Cells with High Hole Extraction Efficiency and Conductivity

Despite great progress in the photovoltaic conversion efficiency (PCE) of inorganic–organic hybrid perovskite solar cells (PSCs), the large‐scale application of PSCs still faces serious challenges due to the poor‐stability and high‐cost of the spiro‐OMeTAD hole transport layer (HTL). It is of great fundamental importance to rationally address the issues of hole extraction and transfer arising from HTL‐free PSCs. Herein, a brand‐new PSC architecture is designed by introducing multigraded‐heterojunction (GHJ) inorganic perovskite CsPbBr_x I_3?x layers as an efficient HTL. The grade adjustment can be achieved by precisely tuning the halide proportion and distribution in the CsPbBr_x I_3?x film to reach an optimal energy alignment of the valance and conduction band between MAPbI₃ and CsPbBr_x I_3?x . The CsPbBr_x I_3?x GHJ as an efficient HTL can induce an electric field where a valance/conduction band edge is leveraged to bend at the heterojunction interface, boosting the interfacial electron–hole splitting and photoelectron extraction. The GHJ architecture enhances the hole extraction and conduction efficiency from the MAPbI₃ to the counter electrode, decreases the recombination loss during the hole transfer, and benefits in increasing the open‐circuit voltage. The optimized HTL‐free PCS based on the GHJ architecture demonstrates an outstanding thermal stability and a significantly improved PCE of 11.33%, nearly 40% increase compared with 8.16% for pure HTL‐free devices.     

Tailoring C60 for Efficient Inorganic CsPbI2Br Perovskite Solar Cells and Modules

Although inorganic perovskite solar cells (PSCs) are promising in thermal stability, their large open-circuit voltage (V_OC) deficit and difficulty in large-area preparation still limit their development toward commercialization. The present work tailors C₆₀ via a codoping strategy to construct an efficient electron-transporting layer (ETL), leading to a significant improvement in V_OC of the inverted inorganic CsPbI₂Br PSC. Specifically, tris(pentafluorophenyl)borane (TPFPB) is introduced as a dopant to lower the lowest unoccupied molecular orbital (LUMO) level of the C₆₀ layer by forming a Lewis acidic adduct. The enlarged free energy difference provides a favorable enhancement in electron injection and thereby reduces charge recombination. Subsequently, a nonhygroscopic lithium salt (LiClO₄) is added to increase electron mobility and conductivity of the film, leading to a reduction in the device hysteresis and facilitating the fabrication of a large-area device. Finally, the as-optimized inorganic CsPbI₂Br PSCs gain a champion power conversion efficiency (PCE) of 15.19%, with a stabilized power output (SPO) of 14.21% (0.09 cm²). More importantly, this work also demonstrates a record PCE of 14.44% for large-area inorganic CsPbI₂Br PSCs (1.0 cm²) and reports the first inorganic perovskite solar module with the excellent efficiency exceeding 12% (10.92 cm²) by a self-developed quasi-curved heating method.     

Indium‐Free Perovskite Solar Cells Enabled by Impermeable Tin‐Oxide Electron Extraction Layers

Corrosive precursors used for the preparation of organic–inorganic hybrid perovskite photoactive layers prevent the application of ultrathin metal layers as semitransparent bottom electrodes in perovskite solar cells (PVSCs). This study introduces tin‐oxide (SnO_x) grown by atomic layer deposition (ALD), whose outstanding permeation barrier properties enable the design of an indium‐tin‐oxide (ITO)‐free semitransparent bottom electrode (SnO_x/Ag or Cu/SnO_x), in which the metal is efficiently protected against corrosion. Simultaneously, SnO_x functions as an electron extraction layer. We unravel the spontaneous formation of a PbI₂ interfacial layer between SnO_x and the CH₃NH₃PbI₃ perovskite. An interface dipole between SnO_x and this PbI₂ layer is found, which depends on the oxidant (water, ozone, or oxygen plasma) used for the ALD growth of SnO_x. An electron extraction barrier between perovskite and PbI₂ is identified, which is the lowest in devices based on SnO_x grown with ozone. The resulting PVSCs are hysteresis‐free with a stable power conversion efficiency (PCE) of 15.3% and a remarkably high open circuit voltage of 1.17 V. The ITO‐free analogues still achieve a high PCE of 11%.     

Stability of Halide Perovskite Solar Cell Devices: In Situ Observation of Oxygen Diffusion under Biasing

Using in situ electrical biasing transmission electron microscopy, structural and chemical modification to n–i–p‐type MAPbI₃ solar cells are examined with a TiO₂ electron‐transporting layer caused by bias in the absence of other stimuli known to affect the physical integrity of MAPbI₃ such as moisture, oxygen, light, and thermal stress. Electron energy loss spectroscopy (EELS) measurements reveal that oxygen ions are released from the TiO₂ and migrate into the MAPbI₃ under a forward bias. The injection of oxygen is accompanied by significant structural transformation; a single‐crystalline MAPbI₃ grain becomes amorphous with the appearance of PbI₂. Withdrawal of oxygen back to the TiO₂, and some restoration of the crystallinity of the MAPbI₃, is observed after the storage in dark under no bias. A subsequent application of a reverse bias further removes more oxygen ions from the MAPbI₃. Light current–voltage measurements of perovskite solar cells exhibit poorer performance after elongated forward biasing; recovery of the performance, though not complete, is achieved by subsequently applying a negative bias. The results indicate negative impacts on the device performance caused by the oxygen migration to the MAPbI₃ under a forward bias. This study identifies a new degradation mechanism intrinsic to n–i–p MAPbI₃ devices with TiO₂.     

Targeted Therapy for Interfacial Engineering Toward Stable and Efficient Perovskite Solar Cells

The poor long‐term stability of organic–inorganic hybrid halide perovskite solar cells (pero‐SCs) remains a big challenge for their commercialization. Although strategies such as encapsulation, doping, and passivation have been reported, there remains a lack of understanding of the water resistance and thermal stability of pero‐SCs. A fullerene derivative, [6,6]‐phenyl‐C₆₁‐butyric acid‐N,N‐dimethyl‐3‐(2‐thienyl)propanam ester (PCBB‐S‐N) containing a functional sulfur atom and C_60, is synthesized and employed as electron transporting layer (ETL)/intermediary layer to targetedly heal the multitype defects in pero‐SCs or assist the growth of ETL, such as [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM), in planar p‐i‐n pero‐SCs. The repaired pero‐SCs can not only dramatically improve their power conversion efficiencies, but also address stability issues under moisture and high temperature. The corresponding mechanism of PCBB‐S‐N with targeted therapy effect in a device is systematically investigated by both experiments and theoretical calculation. This work demonstrates that the proposed fullerene derivative with finely tuned chemical structure can be a promising ETL candidate or intermediary to approach stable and efficient planar p‐i‐n pero‐SCs.     

Improving the Electron Transport Performance of TiO2 Film by Regulating TiCl4 Post-Treatment for High-Efficiency Carbon-Based Perovskite Solar Cells

Titanium oxide (TiO₂) has been widely used as an electron transport layer (ETL) in perovskite solar cells (PSCs). Typically, TiCl₄ post-treatment is indispensable for modifying the surfaces of TiO₂ ETL to improve the electron transport performance. However, it is challenging to produce the preferred anatase phase-dominated TiO₂ by the TiCl₄ post-treatment due to the higher thermodynamic stability of the rutile phase. In this work, a mild continuous pH control strategy for effectively regulating the hydrolysis process of TiCl₄ post-treatment is proposed. As the weak organic base, urea has been demonstrated can maintain a moderate pH decrease during the hydrolysis process of TiCl₄ while keeping the hydrolysis process relatively mild due to the ultra-weak alkalinity. The improved pH environment is beneficial for the formation of anatase TiO₂. Consequently, a uniform anatase-dominated TiO₂ surface layer is formed on the mesoporous TiO₂, resulting in reduced defect density and superior band energy level. The interfacial charge recombination is effectively suppressed, and the charge extraction efficiency is improved simultaneously in the fabricated solar cells. The efficiency of the fabricated carbon electrode-based PSCs (C-PSCs) is improved from 16.63% to 18.08%, which is the highest for C-PSCs based on wide-bandgap perovskites.     

S‐Doped Carbon Fibers Uniformly Embedded with Ultrasmall TiO2 for Na+/Li+ Storage with High Capacity and Long‐Time Stability

Building a rechargeable battery with high capacity, high energy density, and long lifetime contributes to the development of novel energy storage devices in the future. Although carbon materials are very attractive anode materials for lithium‐ion batteries (LIBs), they present several deficiencies when used in sodium‐ion batteries (SIBs). The choice of an appropriate structural design and heteroatom doping are critical steps to improve the capacity and stability. Here, carbon‐based nanofibers are produced by sulfur doping and via the introduction of ultrasmall TiO₂ nanoparticles into the carbon fibers (CNF‐S@TiO₂). It is discovered that the introduction of TiO₂ into carbon nanofibers can significantly improve the specific surface area and microporous volume for carbon materials. The TiO₂ content is controlled to obtain CNF‐S@TiO₂‐5 to use as the anode material for SIBs/LIBs with enhanced electrochemical performance in Na⁺/Li⁺ storage. During the charge/discharge process, the S‐doping and the incorporation of TiO₂ nanoparticles into carbon fibers promote the insertion/extraction of the ions and enhance the capacity and cycle life. The capacity of CNF‐S@TiO₂‐5 can be maintained at ≈300 mAh g^?1 over 600 cycles at 2 A g^?1 in SIBs. Moreover, the capacity retention of such devices is 94%, showing high capacity and good stability.     

TiO2 and Co Nanoparticle‐Decorated Carbon Polyhedra as Efficient Sulfur Host for High‐Performance Lithium–Sulfur Batteries

Metal organic frameworks (MOFs)‐derived porous carbon is proposed as a promising candidate to develop novel, tailorable structures as polysulfides immobilizers for lithium–sulfur batteries because of their high‐efficiency electron conductive networks, open ion channels, and abundant central ions that can store a large amount of sulfur and trap the easily soluble polysulfides. However, most central ions in MOFs‐derived carbon framework are encapsulated in the carbon matrix so that their exposures as active sites to adsorb polysulfides are limited. To resolve this issue, highly dispersed TiO₂ nanoparticles are anchored into the cobalt‐containing carbon polyhedras that are converted from ZIF‐67. Such a type of TiO₂ and Co nanoparticles‐decorated carbon polyhedras (C? Co/TiO₂) provide more exposed active sites and much stronger chemical trapping for polysulfides, hence improving the sulfur utilization and enhancing reaction kinetics of sulfur‐containing cathode simultaneously. The sulfur‐containing carbon polyhedras decorated with TiO₂ nanoparticles (S@C? Co/TiO₂) show a significantly improved cycling stability and rate capability, and deliver a discharge capacity of 32.9% higher than that of TiO₂‐free S@C? Co cathode at 837.5 mA g^?1 after 200 cycles.     

Controlled growth of perovskite KMnF3 upconverting nanocrystals for near-infrared light-sensitive perovskite solar cells and photodetectors

Utilization of the photon upconversion (UC) in Pb halide-based perovskite solar cells (PVSCs) and photodetectors is a potential strategy towards broadening the spectral response from the visible to the near-infrared region and decreasing the non-absorption loss of solar energy. Nevertheless, the implementation of upconverting nanomaterials in these photoelectric devices still faces some barriers. Herein, we report a facile and ethylenediamine tetraacetic acid disodium (EDTAD)-assisted hydrothermal approach for growth of rare-earth-element-doped KMnF₃ nanocrystals with controllable size and a singular red upconverting emission. EDTAD was demonstrated as a useful chelating agent to regulate the nanomaterial size, morphology and UC emission properties. KMnF₃:Yb³⁺, Er³⁺ nanocrystals assisted by EDTAD achieved an intense single-band red UC emission. The formed singular UCNCs were successfully applied as an additive to enhance the photovoltaic performance of the PVSC devices. We found proper molar ratio UCNCs as an additive to the perovskite precursor facilitated the growth of semiconductor perovskite, inducing the development of the perovskite film with improved crystallinity, compact grains and fewer defects. At an optimum molar proportion of UCNCs, the mean power conversion efficiency (PCE) of 18.73% was acquired for PVSCs with KMnF₃:Yb³⁺, Er³⁺ under AM 1.5G, demonstrating a prominent improvement over 25% in average PCE relating to the corresponding value (14.94%) of the PVSC device without UCNCs. Moreover, this singular red emission UCNCs-embedded PVSC was able to work as a photodetector under 980 nm illumination and with a responsivity of 0.26 mA/W.

Graphical abstract