40.1% Record Low-Light Solar-Cell Efficiency by Holistic Trap-Passivation using Micrometer-Thick Perovskite Film

Perovskite Solar Cells and Light Emitting Diodes: Materials Chemistry, Device Physics and Relationship

Solution-processed perovskite solar cells (PSCs) and perovskite light emitting diodes (PeLEDs) represent promising next-generation optoelectronic technologies. This Review summarizes recent advancements in the application of metal halide perovskite materials for PSC and PeLED devices to address the efficiency, stability and scalability issues. Emphasis is placed on material chemistry strategies used to control and engineer the composition, deposition process, interface and micro-nanostructure in solution-processed perovskite films, leading to high-quality crystalline thin films for optimal device performance. Furthermore, we retrospectively compare the device physics of PSCs and PeLEDs, their working principles and their energy loss mechanisms, examining the similarities and differences between the two types of devices. The reciprocity relationship suggests that a great PSC should also be a great PeLED, motivating the search for interconverting photoelectric bifunctional devices with maximum radiative recombination and negligible non-radiative recombination. Specific requirements of PSCs and PeLEDs in terms of bandgap, thickness, band alignment and charge transport to achieve this target are discussed in detail. Further challenges and issues are also illustrated, together with prospects for future development. Understanding these fundamentals, embracing recent breakthroughs and exploring future prospects pave the way toward the rational design and development of high-performance PSC and PeLED devices.

Reducing the Voc Loss of Hole Transport Layer-Free Carbon-Based Perovskite Solar Cells via Dual Interfacial Passivation

The hole transport layer (HTL)-free carbon-based perovskite solar cells (C-PSCs) are promising for commercialization owing to their excellent operational stability and simple fabrication process. However, the power conversion efficiencies (PCE) of C-PSCs are inferior to the metal electrode-based devices due to their open-circuit voltage (Voc) loss. Herein, time-resolved confocal photoluminescence microscopy reveals that grain boundary defects at the perovskite/carbon interface are very likely to function as nonradiative recombination centers in HTL-free C-PSCs. A versatile additive Li2CO3 is used to modify the conformal tin oxide electron transport layer for HTL-free C-PSCs. Li2CO3 modification can result in enhanced charge extraction and optimized energy alignment at electron transport layer/perovskite interface, as well as suppressed defects at perovskite top surface due to Li2CO3-induced formation of PbI2 crystallites. Such dual interfacial passivation ultimately leads to significantly improved Voc up to 1.142 V, which is comparable to the metal electrode-based devices with HTL. Moreover, a record-high PCE of 33.2% is achieved for Li2CO3-modified C-PSCs under weak light illumination conditions, demonstrating excellent indoor photovoltaic performance. This work provides a practical approach to fabricate low-cost, highly efficient carbon-based perovskite solar cells.

Wide Bandgap Perovskites: A Comprehensive Review of Recent Developments and Innovations

Recent advances in wide-bandgap (WBG) perovskite solar cells (PSCs) demonstrate a burgeoning potential to significantly enhance photovoltaic efficiencies beyond the Shockley-Queisser limit for single-junction cells. This review explores the multifaceted improvements in WBG PSCs, focusing on novel compositions, halide substitution strategies, and innovative device architectures. The substitution of iodine with bromine and organic ions such as FA and MA with Cs in the perovskite lattice is emphasized for its effectiveness in achieving higher open-circuit voltages and reduced thermalization losses. Furthermore, the integration of advanced charge transport layers and interface engineering techniques is discussed as critical to minimizing open-circuit voltage (VOC) deficits and improving the photo-stability of these cells. The utilization of WBG PSCs in diverse applications such as semitransparent devices, indoor photovoltaics, and multijunction tandem devices is also explored, addressing both their current limitations and potential solutions. The review culminates in a comprehensive assessment of the current challenges impeding the industrial scale-up of WBG PSC technology and offers a perspective on future research directions aimed at realizing highly efficient and stable WBG PSCs for commercial photovoltaic applications.

Highly Efficient Indoor Perovskite Solar Cells with 40% Efficiency Using Perylene Diimide-Based Zwitterionic Cathode Interlayers

Metal halide perovskites are ideal candidates for indoor photovoltaics (IPVs) due to their tunable bandgaps, which allow the active layers to be optimized for artificial light sources. However, significant non-radiative carrier recombination under low-light conditions has limited the full potential of perovskite-based IPVs. To address this challenge, an integration of perylene diimide (PDI)-based sulfobetaines as cathode interlayers (CILs) is proposed and the impact of varying alkyl chain length (from 1,2-ethylene to 1,5-pentylene) between the cationic and the anionic moieties is examined. The respective four PDI materials are synthesized almost qualitatively using a one-step microwave-assisted process. All of them show adequate thermal stability and energy levels suitable for the desired application as CILs. Moreover, their degradation temperature, LUMO level, conductivity, and performance in model devices are found to change positively along with the alkyl chain length increase. Among the tested derivatives, the compound equipped with the longest alkyl chain (PDI-C5-S3) stands out for its superior electrical conductivity and enhanced ability to lower the silver cathode work function. When incorporated into Cs0.18FA0.82Pb(I0.8Br0.2)-based wide-bandgap perovskite solar cells (PSCs), the PDI-C5-S3 interlayer lead to an outstanding power conversion efficiency (PCE) of 19.04% under one-sun illumination and a remarkable 40.72% under 3000K LED (1000 lux) conditions.

Indoor light energy harvesting perovskite solar cells: from device physics to AI-driven strategies

The rapid advancement of indoor perovskite solar cells (IPSCs) stems from the growing demand for sustainable energy solutions and the proliferation of internet of things (IoT) devices. With tunable bandgaps and superior light absorption properties, perovskites efficiently harvest energy from artificial light sources like LEDs and fluorescent lamps, positioning IPSCs as a promising solution for powering smart homes, sensor networks, and portable electronics. In this review, we introduce recent research that highlights advancements in material optimization under low-light conditions, such as tailoring wide-bandgap perovskites to match indoor light spectra and minimizing defects to enhance stability. Notably, our review explores the integration of artificial intelligence (AI) and machine learning (ML), which are transforming IPSC development by facilitating efficient material discovery, optimizing device architectures, and uncovering degradation mechanisms. These advancements are driving the realization of sustainable indoor energy solutions for interconnected smart technologies.

Multi-cation synergy improves crystallization and antioxidation of CsSnBr3for lead-free perovskite light-emitting diodes

Tin (Sn) perovskites have emerged as promising alternatives to address the toxicity concerns associated with lead-based (Pb) perovskite light-emitting diodes (PeLEDs). However, the inherent oxidation of Sn perovskite films leads to a serious efficiency roll-off in PeLEDs at increased current densities. Although three-dimensional CsSnBr3perovskites exhibit decent carrier mobilities and thermal stability, their rapid crystallization during solution processing results in inadequate surface coverage. This inadequate coverage increases non-radiative recombination and leakage current, thereby hindering Sn PeLED performance. Herein, we present a multi-cation synergistic strategy by introducing the organic cations formamidinium (FA+) and thiophene ethylamine (TEA+) into CsSnBr3perovskites. The addition of organic cations delays crystallization by forming hydrogen bonds interacting with the CsSnBr3. The smaller FA+enters the perovskite lattice and improves crystallinity, while the larger TEA+cation enhances surface coverage and passivates defect states. By further optimizing the interface between PEDOT:PSS and perovskite layers through the use of ethanolamine and a thin layer of LiF, we achieved a red Sn-based PeLED with an emission wavelength of 670 nm, a maximum luminance of 151 cd m-2, and an external quantum efficiency of 0.21%.

Advances in materials and devices for smartlife photovoltaic innovations

The rapid development of photovoltaic (PV) technologies is expanding their applications beyond conventional outdoor energy harvesting into innovative smart-life energy solutions. This review examines the most recent progress in materials and device designs for various emerging PV systems, particularly in indoor and low-light environments, semitransparent devices, and flexible, wearable applications. These advancements have great potential to support autonomous smart life, enhance the energy efficiency of building-integrated solutions, and improve wearable technologies. Despite these gains, challenges such as improving efficiency, durability, scalability, and affordability remain, requiring interdisciplinary collaboration and further research to fully unlock PV technologies' role in sustainable, energy-efficient smart life.

Multifunctional Organic Molecule for Defect Passivation of Perovskite for High-Performance Indoor Solar Cells

Perovskite solar cells (PSCs) can utilize the residual photons from indoor light and continuously supplement the energy supply for low-power electron devices, thereby showing the great potential for sustainable energy ecosystems. However, the solution-processed perovskites suffer from serious defect stacking within crystal lattices, compromising the low-light efficiency and operational stability. In this study, we designed a multifunctional organometallic salt named sodium sulfanilate (4-ABS), containing both electron-donating amine and sulfonic acid groups to effectively passivate the positively-charged defects, like under-coordinated Pb ions and iodine vacancies. The strong chemical coordination of 4-ABS with the octahedra framework can further regulate the crystallization kinetics of perovskite, facilitating the enlarged crystal sizes with mitigated grain boundaries within films. The synergistic optimization effects on trap suppression and crystallization modulation upon 4-ABS addition can reduce energy loss and mitigate ionic migration under low-light conditions. As a result, the optimized device demonstrated an improved power conversion efficiency from 22.48% to 24.34% and achieved an impressive efficiency of 41.11% under 1000 lux weak light conditions. This research provides an effective defect modulation strategy for synergistically boosting the device efficiency under standard and weak light irradiations.

Minimizing Voltage Deficit in Perovskite Indoor Photovoltaics by Interfacial Engineering

Metal halide perovskites with bandgap of ≈1.8 eV are competitive candidates for indoor photovoltaic (IPV) devices, owing to their superior photovoltaic properties and ideal absorption spectra matched to most indoor light sources. However, these perovskite IPVs suffer from severe trap induced non-radiative recombination, resulting in large open-circuit voltage (VOC) losses, particularly under low light intensity. Herein, an effective approach is developed to minimizing trap density by modifying the buried interface of perovskite layer with bifunctional molecular 2-(4-Fluorophenyl)ethylamine Hydrobromide (F-PEABr). The benzene ring of F-PEABr molecules can firmly anchor at the hole transporting layer by π-π stacking interaction, and the other ends can passivate the defects on the buried interface of perovskite layer. Based on that, the F-PEABr modified perovskite IPVs achieved power conversion efficiency (PCE) of 42.3% with a remarkable VOC of 1.13 V under 1000 lux illumination from a 4000 K LED lamp. Finally, perovskite IPV mini-modules with area of 10.40 cm2 are demonstrated with a PCE of 35.2%. This interface modification strategy paves the way for crafting high-performance perovskite IPVs, holding great potential for self-powered internet of things applications.

Enhancing Hole Transport Uniformity for Efficient Inverted Perovskite Solar Cells through Optimizing Buried Interface Contacts and Suppressing Interface Recombination

[4-(3,6-dimethyl-9H-carbazol-9yl)butyl]phosphonic acid (Me-4PACz) self-assembly material has been recognized as a highly effective approach for mitigating nickel oxide (NiOx) surface-related challenges in inverted perovskite solar cells (IPSCs). However, its uneven film generation and failure to effectively passivate the buried interface defects limit the device's performance improvement potential. Herein, p-xylylenediphosphonic acid (p-XPA) containing bilateral phosphate groups (-PO3H2) is introduced as an interface layer between the NiOx/Me-4PACz and the perovskite layer. P-XPA can flatten the surface of hole transport layer and optimize interface contact. Meanwhile, p-XPA achieves better energy level alignment and promotes interfacial hole transport. In addition, the bilateral -PO3H2 of p-XPA can chelate with Pb2+ and form hydrogen bond with FA+ (formamidinium cation), thereby suppressing buried interface non-radiative recombination loss. Consequently, the IPSC with p-XPA buried interface modification achieves champion power conversion efficiency of 25.87 % (certified at 25.45 %) at laboratory scale (0.0448 cm2). The encapsulated target device exhibits better operational stability. Even after 1100 hours of maximum power point tracking at 50 °C, its efficiency remains at an impressive 82.7 % of the initial efficiency. Molecules featuring bilateral passivation groups optimize interfacial contact and inhibit interfacial recombination, providing an effective approach to enhancing the stability and efficiency of devices.

Insights from Theoretical Modeling of Cesium-Formamidinium-Based Mixed-Halide Perovskite Solar Cells for Outdoor and Indoor Applications

This study presents an in-depth computational analysis of hybrid organic-inorganic lead halide perovskite solar cells (PSCs) with a composition of Cs0.17FA0.83Pb(Br0.4I0.6)3 (FA: formamidinium) material under cool and warm light-emitting diodes (LEDs). We propose a novel design of an inverted (p-i-n) PSC to compare the power conversion efficiencies (PCEs) of opaque and semitransparent models under the AM1.5G spectrum and indoor LED lighting. The Shockley-Queisser (SQ) limits were estimated for LEDs with color temperatures of 3000 and 6000 K, revealing significant differences in PCE compared to standard solar radiation. The optical and electrical properties of the perovskite devices were simulated by using the transfer-matrix method and one-dimensional drift-diffusion model. We report a PCE of 15.8% for opaque devices under the AM1.5G spectrum, while the semitransparent devices exhibit PCEs of 12.07% and 10.17% for front and rear illumination, respectively. Under indoor conditions with cool LED lighting, the opaque devices demonstrate a significantly higher PCE of 28.38% and an impressive photovoltage of 1.17 V, surpassing the semitransparent devices, which show efficiencies of approximately 19.5% (front illumination) and 18.3% (rear illumination). While the interface between the hole transport layer and perovskite has a major impact on the device performance of opaque solar cells, the perovskite/electron transport layer junction plays a more critical role in the performance of semitransparent solar cells. The power densities for opaque devices reached up to 106.25 μW/cm2 under cool LED and 97.1 μW/cm2 with warm LED illumination. For semitransparent devices, the power densities exceeded 60.71 μW/cm2 on front-side illumination and 73.66 μW/cm2 on rear illumination under cool LEDs. These results emphasize the significant potential of hybrid PSCs for efficient energy harvesting under various lighting conditions, making them promising candidates for powering low-energy-consumption electronics in indoor environments.

Performance of Triple-Cation Perovskite Solar Cells under Different Indoor Operating Conditions

We systematically analyze triple-cation perovskite solar cells for indoor applications. A large number of devices with different bandgaps from 1.6 to 1.77 eV were fabricated, and their performance under 1-sun AM1.5 and indoor white light emitting diode (LED) light was compared. We find that the trends agree well with the detailed balance limit; however, the devices near the optimal bandgap (1.77 eV) perform worse due to the lower perovskite quality. Instead, we achieve the highest power conversion efficiency (PCE) of 34.0% under 870 lx with 1.67 eV and Al2O3 passivation. The perovskite with a bandgap of 1.71 eV is not far behind, with a high VOC of 1.02 V. Measurements under different white LED color temperatures confirm that the highest PCE is achieved under the warmest colors. All measurements were carried out in a dedicated indoor setup that ensures the diffuse light typical of indoor environments and allows both short- and long-term measurements. In the best case, we observe no degradation during the 33-day test under simulated office conditions with regular switching on and off of the light and a T80 of 30 days under continuous illumination. The results were obtained from multiple batches, which corroborates our findings and gives them statistical relevance.

The Promise and Challenges of Inverted Perovskite Solar Cells

Recently, there has been an extensive focus on inverted perovskite solar cells (PSCs) with a p-i-n architecture due to their attractive advantages, such as exceptional stability, high efficiency, low cost, low-temperature processing, and compatibility with tandem architectures, leading to a surge in their development. Single-junction and perovskite-silicon tandem solar cells (TSCs) with an inverted architecture have achieved certified PCEs of 26.15% and 33.9% respectively, showing great promise for commercial applications. To expedite real-world applications, it is crucial to investigate the key challenges for further performance enhancement. We first introduce representative methods, such as composition engineering, additive engineering, solvent engineering, processing engineering, innovation of charge transporting layers, and interface engineering, for fabricating high-efficiency and stable inverted PSCs. We then delve into the reasons behind the excellent stability of inverted PSCs. Subsequently, we review recent advances in TSCs with inverted PSCs, including perovskite-Si TSCs, all-perovskite TSCs, and perovskite-organic TSCs. To achieve final commercial deployment, we present efforts related to scaling up, harvesting indoor light, economic assessment, and reducing environmental impacts. Lastly, we discuss the potential and challenges of inverted PSCs in the future.

Semi-Opaque Perovskite Solar Cells

Transparent photovoltaics are garnering significant interest for power generation in applications where light transmission is required. Metal halide perovskites have emerged as one of the most lucrative material classes for such device architectures due to their exceptional optoelectronic properties, and compositional versatility enabling a wide range of transparency levels. While research has primarily focused on semitransparent solar cell architectures, their colored appearance, and efficiency limitations hinder their practical applicability. In this perspective, we look at semiopaque perovskite solar cells as an alternative technological approach that comprises partially covered surfaces to enable light transmission. Our comparative analysis reveals that such semiopaque devices have the potential for superior efficiencies while maintaining a color-neutral appearance. These benefits are met with a number of hurdles, which provide key areas for future innovation to see the realization of such devices in real world applications.

Additive engineering for Sb2S3 indoor photovoltaics with efficiency exceeding 17

Indoor photovoltaics (IPVs) have attracted increasing attention for sustainably powering Internet of Things (IoT) electronics. Sb2S3 is a promising IPV candidate material with a bandgap of ~1.75 eV, which is near the optimal value for indoor energy harvesting. However, the performance of Sb2S3 solar cells is limited by nonradiative recombination, which is dependent on the quality of the absorber films. Additive engineering is an effective strategy to fine tune the properties of solution-processed films. This work shows that the addition of monoethanolamine (MEA) into the precursor solution allows the nucleation and growth of Sb2S3 films to be controlled, enabling the deposition of high-quality Sb2S3 absorbers with reduced grain boundary density, optimized band positions, and increased carrier concentration. Complemented with computations, it is revealed that the incorporation of MEA leads to a more efficient and energetically favorable deposition for enhanced heterogeneous nucleation on the substrate, which increases the grain size and accelerates the deposition rate of Sb2S3 films. Due to suppressed carrier recombination and improved charge-carrier transport in Sb2S3 absorber films, the MEA-modulated Sb2S3 solar cell yields a power conversion efficiency (PCE) of 7.22% under AM1.5 G illumination, and an IPV PCE of 17.55% under 1000 lux white light emitting diode (WLED) illumination, which is the highest yet reported for Sb2S3 IPVs. Furthermore, we construct high performance large-area Sb2S3 IPV minimodules to power IoT wireless sensors, and realize the long-term continuous recording of environmental parameters under WLED illumination in an office. This work highlights the great prospect of Sb2S3 photovoltaics for indoor energy harvesting.

Adhesion-Controlled Heterogeneous Nucleation of Tin Halide Perovskites for Eco-Friendly Indoor Photovoltaics

The rapid development of the Internet of Things (IoT) has accelerated the advancement of indoor photovoltaics (IPVs) that directly power wireless IoT devices. The interest in lead-free perovskites for IPVs stems from their similar optoelectronic properties to high-performance lead halide perovskites, but without concerns about toxic lead leakage in indoor environments. However, currently prevalent lead-free perovskite IPVs, especially tin halide perovskites (THPs), still exhibit inferior performance, arising from their uncontrollable crystallization. Here, a novel adhesive bonding strategy is proposed for precisely regulating heterogeneous nucleation kinetics of THPs by introducing alkali metal fluorides. These ionic adhesives boost the work of adhesion at the buried interface between substrates and perovskite film, subsequently reducing the contact angle and energy barrier for heterogeneous nucleation, resulting in high-quality THP films. The resulting THP solar cells achieve an efficiency of 20.12% under indoor illumination at 1000 lux, exceeding all types of lead-free perovskite IPVs and successfully powering radio frequency identification-based sensors.

Organic indoor PV: vanishing surface recombination allows for robust device architecture

As a promising candidate to drive low-power, off-grid applications, organic indoor photovoltaics are beginning to attract research and commercial attention. In organic photovoltaic devices, charge transport layers are often used to promote the extraction of majority carriers, while blocking minority carriers. They can however be a source of device degradation and introduce additional complexity to the fabrication of the device stack. Here, a simplified, yet performant indoor OPV architecture is demonstrated with extended absorber thickness and without electron transport layer (ETL). We show that the diminished impact of the ETL on indoor OPV results from a drastically reduced surface recombination in thick absorber devices. However, the ETL remains important under strong, outdoor illumination, since in that case the reduced surface recombination is overwhelmed by bulk recombination. The proposed simplified device architecture with thick absorber (>500 nm) has great potential in large-scale production of indoor OPV.

Stable and Lead-Safe Polyphenol-Encapsulated Perovskite Solar Cells

Lead (Pb) halide perovskite solar cells (PSCs) exhibit impressive power conversion efficiencies close to those of their silicon counterparts. However, they suffer from moisture instability and Pb safety concerns. Previous studies have endeavoured to address these issues independently, yielding minimal advancements. Here, a general nanoencapsulation platform using natural polyphenols is reported for Pb-halide PSCs that simultaneously addresses both challenges. The polyphenol-based encapsulant is solution-processable, inexpensive (≈1.6 USD m-2), and requires only 5 min for the entire process, highlighting its potential scalability. The encapsulated devices with a power conversion efficiency of 20.7% retained up to 80% of their peak performance for 2000 h and up to 70% for 7000 h. Under simulated rainfall conditions, the encapsulant rich in catechol groups captures the Pb ions released from the degraded perovskites via coordination, keeping the Pb levels within the safe drinking water threshold of 15 ppb.

Influence of the Electron Transport Layer on the Performance of Perovskite Solar Cells under Low Illuminance Conditions

Owing to the tunable band gap of metal-halide perovskite compounds, perovskite solar cells (PSCs) are promising energy-harvesting devices for indoor applications. Since the electron transport layer (ETL) plays a critical role in the performance of PSCs, selecting a suitable ETL is important for improving the performance of PSCs. Here, we compared the characteristics of PSCs employing TiO2 and SnO2, which are widely used as ETLs in PSCs, under low illuminance conditions. Electrochemical impedance spectroscopy revealed that PSCs employing SnO2 as the ETL exhibited lower charge transfer resistance than those employing TiO2 in low light intensity environments. Consequently, SnO2-based PSCs showed a higher power conversion efficiency of 27.7% than that of TiO2-based PSCs (22.5%) under 1000 lx white LED illumination. Space-charge-limited current measurements have shown that the defect density of ETLs strongly affects the performance of PSCs, especially under low illuminance conditions. We believe that this report provides an effective strategy for selecting appropriate ETLs for indoor applications of PSCs.

Ligand Homogenized Br-I Wide-Bandgap Perovskites for Efficient NiOx-Based Inverted Semitransparent and Tandem Solar Cells

Phase heterogeneity of bromine-iodine (Br-I) mixed wide-bandgap (WBG) perovskites has detrimental effects on solar cell performance and stability. Here, we report a heterointerface anchoring strategy to homogenize the Br-I distribution and mitigate the segregation of Br-rich WBG-perovskite phases. We find that methoxy-substituted phenyl ethylammonium (x-MeOPEA+) ligands not only contribute to the crystal growth with vertical orientation but also promote halide homogenization and defect passivation near the buried perovskite/hole transport layer (HTL) interface as well as reduce trap-mediated recombination. Based on improvements in WBG-perovskite homogeneity and heterointerface contacts, NiOx-based opaque WBG-perovskite solar cells (WBG-PSCs) achieved impressive open-circuit voltage (Voc) and fill factor (FF) values of 1.22 V and 83%, respectively. Moreover, semitransparent WBG-PSCs exhibit a PCE of 18.5% (15.4% for the IZO front side) and a high FF of 80.7% (79.4% for the IZO front side) for a designated illumination area (da) of 0.12 cm2. Such a strategy further enables 24.3%-efficient two-terminal perovskite/silicon (double-polished) tandem solar cells (da of 1.159 cm2) with a high Voc of over 1.90 V. The tandem devices also show high operational stability over 1000 h during T90 lifetime measurements.

Flexible Indoor Perovskite Solar Cells by In Situ Bottom-Up Crystallization Modulation and Interfacial Passivation

A robust perovskite-buried interface is pivotal for achieving high-performance flexible indoor photovoltaics as it significantly influences charge transport and extraction efficiency. Herein, a molecular bridge strategy is introduced utilizing sodium 2-cyanoacetate (SZC) additive at the perovskite-buried interface to simultaneously achieve in situ passivation of interfacial defects and bottom-up crystallization modulation, resulting in high-performance flexible indoor photovoltaic applications. Supported by both theoretical calculations and experimental evidences, it illustrates how SZCs serve as molecular bridges, establishing robust bonds between SnO2 transport layer and perovskite, mitigating oxygen vacancy defects and under-coordinated Pb defects at interface during flexible fabrication. This, in turn, enhances interfacial energy level alignment and facilitates efficient carrier transport. Moreover, this in situ investigation of perovskite crystallization dynamics reveals bottom-up crystallization modulation, extending perovskite growth at the buried interface and influencing subsequent surface recrystallization. This results in larger crystalline grains and improved lattice strain of the perovskite during flexible fabrication. Finally, the optimized flexible solar cells achieve an impressive efficiency exceeding 41% at 1000 lux, with a fill factor as high as 84.32%. The concept of the molecular bridge represents a significant advancement in enhancing the performance of perovskite-based flexible indoor photovoltaics for the upcoming era of Internet of Things (IoT).

In Situ Formation of 2D Perovskite Seeding for Record-Efficiency Indoor Perovskite Photovoltaic Devices

With 40% efficiency under room light intensity, perovskite solar cells (PSCs) will be promising power supplies for low-light applications, particularly for Internet of Things (IoT) devices and indoor electronics, shall they become commercialized. Herein, β-alaninamide hydrochloride (AHC) is utilized to spontaneously form a layer of 2D perovskite nucleation seeds for improved film uniformity, crystallization quality, and solar cell performance. It is found that the AHC addition indeed improves film quality as demonstrated by better uniformity, lower trap density, smaller lattice stress, and, as a result, a 10-fold increase in charge carrier lifetime. Consequently, not only does the small-area (0.09 cm2 ) PSCs achieve a power conversion efficiency of 42.12%, the large-area cells (1.00 cm2 , and 2.56 cm2 ) attain efficiency as high as 40.93%, and 40.07% respectively. All of these are the highest efficiency values for indoor photovoltaic cells with similar sizes, and more importantly, they represent the smallest efficiency loss due to area scale-up. This work provides a new method to fabricate high-performance indoor PSCs (i-PSCs) for IoT devices with great potential in large-area printing technology.

High-Performance Indoor Perovskite Solar Cells by Self-Suppression of Intrinsic Defects via a Facile Solvent-Engineering Strategy

Lead halide perovskite solar cells have been emerging as very promising candidates for applications in indoor photovoltaics. To maximize their indoor performance, it is of critical importance to suppress intrinsic defects of the perovskite active layer. Herein, a facile solvent-engineering strategy is developed for effective suppression of both surface and bulk defects in lead halide perovskite indoor solar cells, leading to a high efficiency of 35.99% under the indoor illumination of 1000 lux Cool-white light-emitting diodes. Replacing dimethylformamide (DMF) with N-methyl-2-pyrrolidone (NMP) in the perovskite precursor solvent significantly passivates the intrinsic defects within the thus-prepared perovskite films, prolongs the charge carrier lifetimes and reduces non-radiative charge recombination of the devices. Compared to the DMF, the much higher interaction energy between NMP and formamidinium iodide/lead halide contributes to the markedly improved quality of the perovskite thin films with reduced interfacial halide deficiency and non-radiative charge recombination, which in turn enhances the device performance. This work paves the way for developing efficient indoor perovskite solar cells for the increasing demand for power supplies of Internet-of-Things devices.

Stabilizing Precursor Solution and Controlling Crystallization Kinetics Simultaneously for High-Performance Perovskite Solar Cells

The efficiency of metal halide perovskite solar cells (PSCs) has skyrocketed; however, defects created by aging precursor solutions and during crystallization pose a significant barrier to the reproducibility and efficiency of solar cells. In this work, fluoro-N,N,N″,N″-tetramethylformamidinium hexafluorophosphate (F-(CH3 )4 CN2 PF6 , abbreviated as TFFH) is introduced to stabilize precursor solution and improve crystallization dynamics simultaneously for high-performance formamidinium lead iodide (FAPbI3 )-based perovskite indoor photovoltaics. The TFFH stabilizes the precursor solution by inhibiting oxidation of I- and reducing newly generated I0 to I- , and passivates undercoordinated Pb2+ by interacting with the Pb─I framework. Time-resolved optical diagnostics show prolonged perovskite crystallization dynamics and in situ defect passivation due to the presence of strong FA+ ···TFFH···Pb─I interaction. Simultaneous regulation of precursor solution and crystallization dynamics guarantee larger perovskite grain sizes, better crystal orientation, fewer defects and more efficient charge extraction in PSCs. The optimized PSCs achieve improved reproducibility and better stability and reach an efficiency of 42.43% at illumination of 1002 lux, which is the highest efficiency among all indoor photovoltaics. It is anticipated that the concurrent stabilization of solutions and regulation of crystallization dynamics will emerge as a prevalent approach for enhancing the reproducibility and efficiency of perovskite.

Tandem cells for unbiased photoelectrochemical water splitting

Hydrogen is an essential energy carrier which will address the challenges posed by the energy crisis and climate change. Photoelectrochemical water splitting (PEC) is an important method for producing solar-powered hydrogen. The PEC tandem configuration harnesses sunlight as the exclusive energy source to drive both the hydrogen (HER) and oxygen evolution reactions (OER), simultaneously. Therefore, PEC tandem cells have been developed and gained tremendous interest in recent decades. This review describes the current status of the development of tandem cells for unbiased photoelectrochemical water splitting. The basic principles and prerequisites for constructing PEC tandem cells are introduced first. We then review various single photoelectrodes for use in water reduction or oxidation, and highlight the current state-of-the-art discoveries. Second, a close look into recent developments of PEC tandem cells in water splitting is provided. Finally, a perspective on the key challenges and prospects for the development of tandem cells for unbiased PEC water splitting are given.

Dendrimer Modification Strategy Based on the Understanding of the Photovoltaic Mechanism of a Perovskite Device under Full Sun and Indoor Light

The wide-band-gap inorganic CsPbI₂Br perovskite material provides a highly matched absorption range with the indoor light spectrum and is expected to be used in the fabrication of highly efficient indoor photovoltaic cells (IPVs) and self-powered low-power Internet of Things (IoT) sensors. However, the defects that cause nonradiative recombination and ion migration are assumed to form leakage loss channels, resulting in a severe impact on the open-circuit voltage (V_OC) and the fill factor (FF) of IPVs. Herein, we introduce poly(amidoamine) (PAMAM) dendrimers with multiple passivation sites to fully repair the leakage channels in the devices, taking into account the characteristics of IPVs that are extremely sensitive to nonradiative recombination and shunt resistance. The as-optimized IPVs demonstrate a promising PCE of 35.71% under a fluorescent light source (1000 lux), with V_OC increased from 0.99 to 1.06 V and FF improved from 75.21 to 84.39%. The present work provides insight into the photovoltaic mechanism of perovskites under full sun and indoor light, which provides guidance for perovskite photovoltaic technology with industrialization prospects.

Skin-Interfaced Wearable Sweat Sensors for Precision Medicine

Wearable sensors hold great potential in empowering personalized health monitoring, predictive analytics, and timely intervention toward personalized healthcare. Advances in flexible electronics, materials science, and electrochemistry have spurred the development of wearable sweat sensors that enable the continuous and noninvasive screening of analytes indicative of health status. Existing major challenges in wearable sensors include: improving the sweat extraction and sweat sensing capabilities, improving the form factor of the wearable device for minimal discomfort and reliable measurements when worn, and understanding the clinical value of sweat analytes toward biomarker discovery. This review provides a comprehensive review of wearable sweat sensors and outlines state-of-the-art technologies and research that strive to bridge these gaps. The physiology of sweat, materials, biosensing mechanisms and advances, and approaches for sweat induction and sampling are introduced. Additionally, design considerations for the system-level development of wearable sweat sensing devices, spanning from strategies for prolonged sweat extraction to efficient powering of wearables, are discussed. Furthermore, the applications, data analytics, commercialization efforts, challenges, and prospects of wearable sweat sensors for precision medicine are discussed.

Carbon Electrode with Sputtered Au Coating for Efficient and Stable Perovskite Solar Cells

Halide perovskite solar cells (PSCs) represent a low-cost and high-efficiency solar technology. However, most of the highly efficient PSCs need a noble electrode, such as Au, through thermal evaporation. It is reported that a sputtered Au electrode on a PSC could damage the organic hole transport layer (HTL) and the perovskite layer. Here, we report a simple, yet effective sputtered gold nanoparticle decorated carbon electrode to fabricate efficient and stable planar PSCs. The sputtered Au layer on the doctor-bladed coated carbon electrode can be directly applied to the perovskite semicells by mechanical stacking. By optimizing the gold thickness, a power conversion efficiency (PCE) of 16.87% was obtained for the composite electrode-based PSC, while the reference device recorded a PCE of 12.38%. The composite electrode-based device demonstrated 96% performance retention after being stored under humid conditions (50-60%) without encapsulation for ∼100 h. This demonstrates a promising pathway toward the commercialization of large-scale manufacturable sputtered electrodes for the PSC solar module.

Perspectives for the conversion of perovskite indoor photovoltaics into IoT reality

As a competitive candidate for powering low-power terminals in Internet of Things (IoT) systems, indoor photovoltaic (IPV) technology has attracted much attention due to its effective power output under indoor light illumination. One such emerging photovoltaic technology, perovskite cell, has become a hot topic in the field of IPVs due to its outstanding theoretical performance limits and low manufacturing costs. However, several elusive issues remain limiting their applications. In this review, the challenges for perovskite IPVs are discussed in view of the bandgap tailoring to match indoor light spectra and the defect trapping regulation throughout the devices. Then, we summarize up-to-date perovskite cells, highlighting advanced strategies such as bandgap engineering, film engineering and interface engineering to enhance indoor performance. The investigation of indoor applications of large and flexible perovskite cells and integrated devices powered by perovskite cells is exhibited. Finally, the perspectives for the perovskite IPV field are provided to help facilitate the further improvement of indoor performance.

Recent Strategies for High-Performing Indoor Perovskite Photovoltaics

The development of digital technology has made our lives more advanced as a society familiar with the Internet of Things (IoT). Solar cells are among the most promising candidates for power supply in IoT sensors. Perovskite photovoltaics (PPVs), which have already attained 25% and 40% power conversion efficiencies for outdoor and indoor light, respectively, are the best candidates for self-powered IoT system integration. In this review, we discuss recent research progress on PPVs under indoor light conditions, with a focus on device engineering to achieve high-performance indoor PPVs (Id-PPVs), including bandgap optimization and defect management. Finally, we discuss the challenges of Id-PPVs development and its interpretation as a potential research direction in the field.

2.11 - Accurate characterization of indoor photovoltaic performance

Ambient energy harvesting has great potential to contribute to sustainable development and address growing environmental challenges. Converting waste energy from energy-intensive processes and systems (e.g. combustion engines and furnaces) is crucial to reducing their environmental impact and achieving net-zero emissions. Compact energy harvesters will also be key to powering the exponentially growing smart devices ecosystem that is part of the Internet of Things, thus enabling futuristic applications that can improve our quality of life (e.g. smart homes, smart cities, smart manufacturing, and smart healthcare). To achieve these goals, innovative materials are needed to efficiently convert ambient energy into electricity through various physical mechanisms, such as the photovoltaic effect, thermoelectricity, piezoelectricity, triboelectricity, and radiofrequency wireless power transfer. By bringing together the perspectives of experts in various types of energy harvesting materials, this Roadmap provides extensive insights into recent advances and present challenges in the field. Additionally, the Roadmap analyses the key performance metrics of these technologies in relation to their ultimate energy conversion limits. Building on these insights, the Roadmap outlines promising directions for future research to fully harness the potential of energy harvesting materials for green energy anytime, anywhere.

Efficient Perovskite Indoor Photovoltaics with Open-Circuit Voltage of 1.15 V via Collaborative Optimization of CsPbI2 Br Layer and Hole Transport Layer

All-inorganic CsPbI₂ Br perovskite has attracted great attention due to the stable crystal structure and moisture resistance, and its 1.91 eV bandgap is close to the optimal bandgap of indoor artificial light sources, making it be the best candidate for the indoor photovoltaics (IPVs) to power a wide range of internet of things related electronic devices. Herein, we report on the preparation of CsPbI₂ Br with α-phase and the improvement of its phase stability by adding lead acetate in the CsPbI₂ Br precursor. A series of dopant-free conjugated polymers (P3HT, PBDB-T, and PM6) with different highest occupied molecular orbital energy levels are introduced as hole transport layers for building IPV devices. The PM6 based devices having better energy alignment with perovskite demonstrate best indoor photovoltaic performance, giving a remarkable open-circuit voltage of 1.15 V and high fill factor of 81.86% under 1000 lux (330 µW cm^-2 ) light-emitting diode illumination, and finally realizing a decent power conversion efficiency of 33.68%. Our findings suggest that collaboratively optimize the CsPbI₂ Br layer and hole transport layer is an effective approach to realize high performance IPVs.

Bio-Inspired Graphitic Carbon-Based Large-Area (10 × 10 cm2) Perovskite Solar Cells: Stability Assessments under Indoor, Outdoor, and Water-Soaked Conditions

In the emerging photovoltaic (PV) technologies, the golden triangle rule includes higher efficiency, longevity (or stability), and low cost, which are the foremost criteria for the root of commercial feasibility. Accordingly, a unique low-cost, ecofriendly, all-solution-processed, "bio-inspired" graphitic carbon (extracted from the most invasive plant species of Eichhornia crassipes: listed as one of the 100 most dangerous species by the International Union for Conservation of Nature) and a mixed halide perovskite interface-engineered, unique single-cell large-scale (10 × 10 sq.cm with an active area of 88 cm²) carbon-based perovskite solar cell (C-PSC) are demonstrated for the first time, delivering a maximum PCE of 6.32%. Notable performance was observed under low light performance for the interface-engineered champion device fabricated using the layer-to-layer approach, which, even when tested under fluorescent room light condition (at 200 lux of about ∼0.1 SUN illumination), exhibited a significant PCE. In terms of addressing the stability issues in the fabricated PSC devices, the present work has adopted a two-step strategy: the instability toward the extrinsic factors is addressed by encapsulation, and the subsequent intrinsic instability issue is also addressed through interfacial engineering. Surprisingly, when tested under various stability conditions (STC) such as ambient air, light (continuous 1 SUN, under room light illumination (0.1 SUN) and direct sunlight), severe damp up to a depth of ∼25 mm water (cold (∼15 °C) and hot (∼65 °C)), acidic pH (∼5), and alkaline pH (∼11)) conditions, the fabricated large-scale carbon-based perovskite solar cells (C-LSPSCs) retained unexpected long-term stability in their performance for over 50 days. As to appraise the performance superiority of the fabricated C-LSPSC devices under various aforesaid testing conditions, a working model of a mini-fan has been practically powered and demonstrated.

Addressing gain-bandwidth trade-off by a monolithically integrated photovoltaic transistor

The gain-bandwidth trade-off limits the development of high-performance photodetectors; i.e., the mutual restraint between the response speed and gain has intrinsically limited performance optimization of photomultiplication phototransistors and photodiodes. Here, we show that a monolithically integrated photovoltaic transistor can solve this dilemma. In this structure, the photovoltage generated by the superimposed perovskite solar cell, acting as a float gate, is amplified by the underlying metal oxide field-effect transistor. By eliminating deep-trap defects through processing optimization, we achieved devices with a maximum responsivity close to 6 × 10⁴ A/W, a specific detectivity (D*) of 1.06 × 10¹³ Jones, and an f_3dB of 1.2 MHz at a low driving voltage of 3 V. As a result, a record gain-bandwidth product is achieved. The device further exhibits the advantage in photoplethysmography detection with weak illuminations, where our device accurately detects the detailed features that are out of the capability of conventional photodetectors.

Engineering the Non-Radiative Recombination of Mixed-Halide Perovskites with Optimal Bandgap for Indoor Photovoltaics

Indoor photovoltaics have attracted increasing attention, since they can provide sustainable energy through the recycling of photon energy from household dim lighting. However, solar cells exhibiting high performance under sunlight may not perform well under indoor light conditions, mainly due to the mismatch of the irradiance spectrum. In particular, most of the indoor light sources emit visible photons with negligible near-infrared irradiance. According to the detailed balance theory, the optimal bandgap for indoor photovoltaics should be relatively larger, considering the trade-off between photocurrent and photovoltage losses. In this work, a systematic comparison of the theoretical limits of the conventional and indoor photovoltaics is presented. Then the non-radiative recombination losses are reduced by a synergetic treatment with Pb(SCN)₂ and PEABr, resulting relatively high open circuit voltage of 1.29 V and power conversion efficiency of 17.32% under 1 sun illumination. Furthermore, the devices are fully characterized under weak indoor light (1000 lux, 4000 K LED) achieving a high efficiency of 37.18%, which is promising for real applications.

Effect of Solvent Residue in the Thin-Film Fabrication on Perovskite Solar Cell Performance

Organic-inorganic Pb-based halide perovskite photoelectrical materials, especially perovskite solar cells (PSCs), have attracted attention due to the significant efforts in improving the power conversion efficiency (PCE) to above 25%. However, the stability issue of the PSCs restricts their further development for commercialization. Strategies are designed to keep moisture and oxygen out of the perovskite films, such as additive, surface passivation, and solvent engineering; however, usually, the corrosion of active films by the residual solvent is mostly ignored. Solvent residue is the paramount factor influencing the stability of the perovskite film prepared by the solution method, and most solvents can be easily absorbed and accelerate the perovskite film decomposition. Here, we studied the residual solvent effect on two kinds of perovskite films obtained by different annealing processes: hot air annealing and hot bench annealing. Several detection techniques were used to study the performance of two different annealing methods, including time-of-flight secondary ion mass spectrometry (ToF-SIMS), thermogravimetric analysis (TGA), and field-emission scanning electron microscopy (FESEM). The perovskite film obtained by hot air annealing shows less residual solvent and better device performance than the hot bench annealing method. This method is expected to provide insight into reducing solvent residue to improve the stability of the PSCs, especially for future commercialization.

Simultaneous Passivation of Bulk and Interface Defects with Gradient 2D/3D Heterojunction Engineering for Efficient and Stable Perovskite Solar Cells

Minimizing bulk and interfacial nonradiative recombination losses is key to further improving the photovoltaic performance of perovskite solar cells (PSC) but very challenging. Herein, we report a gradient dimensionality engineering to simultaneously passivate the bulk and interface defects of perovskite films. The 2D/3D heterojunction is skillfully constructed by the diffusion of an amphiphilic spacer cation from the interface to the bulk. The 2D/3D heterojunction engineering strategy has achieved multiple functions, including defect passivation, hole extraction improvement, and moisture stability enhancement. The introduction of tertiary butyl at the spacer cation should be responsible for increased film and device moisture stability. The device with 2D/3D heterojunction engineering delivers a promising efficiency of 22.54% with a high voltage of 1.186 V and high fill factor of 0.841, which benefits from significantly suppressed bulk and interfacial nonradiative recombination losses. Moreover, the modified devices demonstrate excellent light, thermal, and moisture stability over 1000 h. This work paves the way for the commercial application of perovskite photovoltaics.

Hysteresis in hybrid perovskite indoor photovoltaics

Halide perovskite indoor photovoltaics (PV) are a viable solution to autonomously power the billions of sensors in the huge technology field of the Internet of Things. However, there exists a knowledge gap in the hysteresis behaviour of these photovoltaic devices under indoor lighting conditions. The present work is the first experimental study dedicated to exploring the degree of hysteresis in halide perovskite indoor photovoltaic devices by carrying out both transient J-V scan and steady state maximum power point tracking (MPPT) measurements. Dependence of hysteresis on device architecture, selection of electron transporting layers and the composition of the perovskite photoactive layers were investigated. Under indoor illumination, the p-i-n MAPbI₃-based devices show consistently high power conversion efficiency (PCE) (stabilized PCE) of greater than 30% and negligible hysteresis behaviour, whereas the n-i-p MAPbI₃ devices show poor performance (stabilized PCE ∼ 15%) with pronounced hysteresis effect. Our study also reveals that the n-i-p triple cation perovskite devices are more promising (stabilized PCE ∼ 25%) for indoor PV compared to n-i-p MAPbI₃ due to their suppressed ion migration effects. It was observed that the divergence of the PCE values estimated from the J-V scan measurements, and the maximum power point tracking method is higher under indoor illumination compared to 1 Sun, and hence for halide perovskite-based indoor PV, the PCE from the MPPT measurements should be prioritized over the J-V scan measurements. The results from our study suggest the following approaches for maximizing the steady state PCE from halide perovskite indoor PV: (i) select perovskite active layer composition with suppressed ion migration effects (such as Cs-containing triple cation perovskites) and (ii) for the perovskite composition such as MAPbI₃, where the ion migration is very active, p-i-n architecture with organic charge transport layers is beneficial over the n-i-p architecture with conventional metal oxides (such as TiO₂, SnO₂) as charge transport layers. This article is part of the theme issue 'Developing resilient energy systems'.

Full-Dimensional Grain Boundary Stress Release for Flexible Perovskite Indoor Photovoltaics

Perovskite photovoltaics are strong potential candidates to drive low-power off-grid electronics for indoor applications. Compared with rigid devices, flexible perovskite devices can provide a more suitable surface for indoor small electronic devices, enabling them have a broader indoor application prospect. However, the mechanical stability of flexible perovskite photovoltaics is an urgent issue solved. Herein, a kind of 3D crosslinking agent named borax is selected to carry out grain boundary penetration treatment on perovskite film to realize full-dimensional stress release. This strategy improves the mechanical and phase stabilities of perovskite films subjected to external forces or large temperature changes. The fabricated perovskite photovoltaics deliver a champion power conversion efficiency (PCE) of 21.63% under AM 1.5G illumination, which is the highest one to date. The merit of low trap states under weak light makes the devices present a superior indoor PCE of 31.85% under 1062 lux (LED, 2956 K), which is currently the best flexible perovskite indoor photovoltaic device. This work provides a full-dimensional grain boundary stress release strategy for highly stable flexible perovskite indoor photovoltaics.

Biuret Induced Tin-Anchoring and Crystallization-Regulating for Efficient Lead-Free Tin Halide Perovskite Light-Emitting Diodes

Lead-free perovskite emitters, particularly 2D tin (Sn) halide perovskites, have attracted considerable academic attention in recent years. However, the problems of Sn oxidation and rapid crystallization lead to an inferior perovskite morphology with high trap states, thus limiting the luminous efficiency of Sn halide perovskite light-emitting diodes (PeLEDs). In this study, the authors establish an approach by introducing an organic additive, 2-imidodicarbonic diamide (biuret), to address the issues of Sn oxidation and fast crystallization. The unique symmetrical carbonyl groups in the biuret robustly interact with the Sn-I framework, providing a strong Sn-anchoring effect. Consequently, it also suppresses the easy oxidation of Sn²⁺ , regulating the crystallization process simultaneously. Density functional theory (DFT) calculations also confirmed the robust interaction between the biuret and the 2D Sn halide perovskite. Furthermore, the authors demonstrate efficient PeLEDs with saturated red emission at 637 nm, a maximum luminance (L_max ) of 418 cd m^-2 , a maximum external quantum efficiency (EQE_max ) of 1.37%, and a half-life (T₅₀ ) of 288 s. This work provides insights on the microcosmic chemical interaction between organics and 2D Sn halide perovskites, advancing the development of efficient lead-free PeLEDs.

Low-Trap-Density CsPbX3 Film for High-Efficiency Indoor Photovoltaics

The continuous advancement of the Internet of Things (IoT) and photovoltaic technology has promoted the development of indoor photovoltaics (IPVs) that powers wireless devices. Nowadays, the CsPbX₃ perovskite has received widespread attention because of its high power conversion efficiency (PCE) in an indoor environment and suitable band gap for IPVs. In this work, we regulated the thickness of the photoactive layer (to optimize the carrier transport process without affecting indoor absorption) and bromine substitution (to adjust the band gap and improve the quality of the film) to reduce trap-assisted carrier recombination. A CsPbI_2.7Br_0.3 perovskite cell with excellent performance was obtained, which is superior to c-Si cells in a low-light environment. The optimized device achieved PCE values of 32.69 and 33.11% under a 1000 lux fluorescent lamp and white light-emitting diode (WLED) illumination. The J-V hysteresis of the device is also effectively suppressed. Moreover, it has a steady-state output power of 7.76 μW (0.09 cm², and can be enhanced by enlarging the areas), which can meet the consumption of many small wireless devices. It is worth noting that the optimized device has excellent applicability to be used in a complex indoor environment.

Highly Efficient and Stable CsPbTh3 (Th = I, Br, Cl) Perovskite Solar Cells by Combinational Passivation Strategy

The distorted lead iodide octahedra of all-inorganic perovskite based on triple halide-mixed CsPb(I_2.85 Br_0.149 Cl_0.001 ) framework have made a tremendous breakthrough in its black phase stability and photovoltaic efficiency. However, their performance still suffers from severe ion migration, trap-induced nonradiative recombination, and black phase instability due to lower tolerance factor and high total energy. Here, a combinational passivation strategy to suppress ion migration and reduce traps both on the surface and in the bulk of the CsPhTh₃ perovskite film is developed, resulting in improved power conversion efficiency (PCE) to as high as 19.37%. The involvement of guanidinium (GA) into the CsPhTh₃ perovskite bulk film and glycocyamine (GCA) passivation on the perovskite surface and grain boundary synergistically enlarge the tolerance factor and suppress the trap state density. In addition, the acetate anion as a nucleating agent significantly improves the thermodynamic stability of GA-doped CsPbTh₃ film through the slight distortion of PbI₆ octahedra. The decreased nonradiative recombination loss translates to a high fill factor of 82.1% and open-circuit voltage (V_OC ) of 1.17 V. Furthermore, bare CsPbTh₃ perovskite solar cells without any encapsulation retain 80% of its initial PCE value after being stored for one month under ambient conditions.

Rational Surface-Defect Control via Designed Passivation for High-Efficiency Inorganic Perovskite Solar Cells

Iodine vacancies (V_I ) and undercoordinated Pb²⁺ on the surface of all-inorganic perovskite films are mainly responsible for nonradiative charge recombination. An environmentally benign material, histamine (HA), is used to passivate the V_I in perovskite films. A theoretical study shows that HA bonds to the V_I on the surface of the perovskite film via a Lewis base-acid interaction; an additional hydrogen bond (H-bond) strengthens such interaction owing to the favorable molecular configuration of HA. Undercoordinated Pb²⁺ and Pb clusters are passivated, leading to significantly reduced surface trap density and prolonged charge lifetime within the perovskite films. HA passivation also induces an upward shift of the energy band edge of the perovskite layer, facilitating interfacial hole transfer. The combination of the above raises the solar cell efficiency from 19.5 to 20.8 % under 100 mW cm^-2 illumination, the highest efficiency so far for inorganic metal halide perovskite solar cells (PSCs).

Perovskite indoor photovoltaics: opportunity and challenges

With the rapid development of the Internet of Things (IoTs), photovoltaics (PVs) has a vast market supply gap of billion dollars. Moreover, it also puts forward new requirements for the development of indoor photovoltaic devices (IPVs). In recent years, PVs represented by organic photovoltaic cells (OPVs), silicon solar cells, dye-sensitized solar cells (DSSCs), etc. considered for use in IoTs mechanisms have also been extensively investigated. However, there are few reports on the indoor applications of perovskite devices, even though it has the advantages of better performance. In fact, perovskite has the advantages of better bandgap adjustability, lower cost, and easier preparation of large-area on flexible substrates, compared with other types of IPVs. This review starts from the development status of IoTs and investigates the cost, technology, and future trends of IPVs. We believe that perovskite photovoltaics is more suitable for indoor applications and review some strategies for fabricating high-performance perovskite indoor photovoltaic devices (IPVs). Finally, we also put forward a perspective for the long-term development of perovskite IPVs.

Deep-Level Transient Spectroscopy for Effective Passivator Selection in Perovskite Solar Cells to Attain High Efficiency over 23

Most studies choose passivators essentially in a trial-and-error fashion in an attempt to attain high efficiency in perovskite solar cells (PSCs). Using deep-level transient spectroscopy (DLTS) measurements, the type of defects in perovskite films was determined to guide the passivator selection for PSCs. Three kinds of positively charged defects were found in the target PSC system. Fluorinated phenylethylamine hydroiodide (FPEAI) was chosen to passivate the surface defects due to the electronegativity and hydrophobicity of fluorine. Due to the decreased surface roughness, increased hydrophobicity, lowered defect density, and improved carrier dynamics as observed by ultrafast transient absorption spectroscopy (TAS), a PSC with meta-F-PEAI had the best efficiency over 23 % with open-circuit voltage of 1.155 V and fill factor of 80.15 %. In addition, the long-term stability of the PSC was significantly improved. The present work provides a new means to select the best passivator for different types of defects.