Neuromorphic hardware demands device elements that integrate low‐voltage analog memory with neuron‐like dynamics, all integrated into a sustainable materials platform. Halide frameworks offer electronic–ionic coupling essential for brain‐inspired electronics, but lead‐halide perovskites suffer from toxicity and instability. Here, we report triple‐cation antimony–bismuth (Sb–Bi) A3B2I9 perovskite‐inspired memristors exhibiting synaptic plasticity and neuron‐like spiking within a two‐terminal stack. Devices demonstrate reproducible bipolar switching, state retention (≈103 s), and >600 operating cycles. Millisecond pulse trains enable analog potentiation and paired‐pulse facilitation with bi‐exponential decay, while microsecond stimuli induce spiking and oscillatory responses. Bias‐dependent impedance spectroscopy confirms coupled ionic migration and trap‐assisted electronic transport. Integrated into a memristive neural network via hardware–software co‐design, Sb–Bi devices achieve 96.52% classification accuracy, comparable to software‐based network (96.67%). These findings position lead‐free PIMs as less‐toxic, solution‐processable building blocks for ion‐controlled neuromorphic electronics and motivate array‐level demonstrations with extended retention, endurance, and energy benchmarking.

A selective PPDT2FBT back contact reduces leakage and recombination, enabling efficient Cs 2 AgBi 2 I 9 indoor photovoltaics under WLED and mixed office lighting.

Nanotechnology has transformed optoelectronics through quantum dots (QDs), particularly metal halide perovskite QDs (PQDs). PQDs boast high photoluminescent quantum yield, tunable emission, and excellent defect tolerance without extensive passivation. Quantum confinement effects, which refer to the phenomenon where the motion of charge carriers is restricted to a small region, produce discrete energy levels and blue shifts in these materials. They are ideal for next-generation optoelectronic devices prized for superior optical properties, low cost, and straightforward synthesis. In this review, along with the fundamental physics behind the phenomenon, we have covered advances in synthesis methods such as hot injection, ligand-assisted reprecipitation, ultrasonication, solvothermal, and microwave-assisted that enable precise control over size, shape, and stability, enhancing their suitability for LEDs, lasers, and photodetectors. Challenges include lead toxicity and cost, necessitating research into alternative materials and scalable manufacturing. Furthermore, strategies like doping and surface passivation that improve stability and emission control are discussed comprehensively, and how lead halide perovskites like CsPbBr3undergo phase transitions with temperature, impacting device performance, are also investigated. We have explored various characterization techniques, providing insights into nanocrystal properties and behaviors in our study. This review highlights PQDs' synthesis, physical and optoelectronic properties, and potential applications across diverse technologies.

Ion migration and lead toxicity present significant challenges to commercializing lead halide perovskites (LHPs) based solar cells, particularly the presence of lead obstructs their use in indoor photovoltaics (IPVs). Recently, antimony-based perovskite-inspired materials (PIMs) have emerged as promising alternatives for IPVs. However, the detailed understanding of the ion migration pathways in PIMs and their impact on device kinetics and stability remain largely unexplored. The systematic study, comparing ionic conduction in PIMs with the well-studied LHPs, provides broader mechanistic insights into ionic conduction. This comparison highlights the correlation between ionic conduction, anomalous device behavior, and operational stability. The slower ionic conduction in PIMs, resulting from the high formation energy of halide defects, leads to weaker polarization at the interface and, consequently, higher operational stability. The higher non-radiative recombination rate, coupled with lower ionic mobility, leads to a pronounced negative capacitance after a specific applied bias. Furthermore, first-principles calculations explore potential ion migration pathways and their minimum activation energies in PIMs. The work therefore provides valuable insights into ion dynamics in both PIMs and LHPs, with important implications for designing novel materials and advancing future applications.

Efficient surface passivation is crucial for mitigating defect-induced recombination losses in perovskite-based indoor photovoltaics (IPVs), where charge carrier dynamics are particularly sensitive to trap states under low-intensity illumination. Here, we introduce two pyridine-based passivators, tris[4-(pyridin-4-yl)phenyl]amine (TPAP) and its ionic counterpart (TPAP1), to achieve high-performance and stable perovskite IPVs. These passivators strongly coordinate with under-coordinated Pb2+ ions, effectively reducing trap densities and improving hydrophobicity. When incorporated into lead-based triple-cation CsFAMA perovskite films, TPAP and TPAP1 significantly suppress nonradiative recombination, leading to notable improvements in device performance. Remarkably, TPAP1 demonstrates a unique ability to simultaneously passivate multiple defect types, further optimizing charge transport and boosting the open-circuit voltage (VOC). As a result, IPV devices incorporating TPAP and TPAP1 achieved remarkable indoor power conversion efficiencies of 30.1% and 31.7%, with VOC values of 0.97 and 1.00 V, respectively, under 1000 lux white LED illumination. This study presents a scalable and effective strategy for defect passivation in perovskite IPVs, highlighting the critical role of multifunctional organic passivators in advancing next-generation energy harvesting technologies.

Electrolyte-gated semiconductor devices are the building blocks for next-generation optoelectronics due to their memory effect and slow ion kinetics, mimicking synapses. Halide perovskites have memory effects, mixed electronic and ionic conductivity, and optical responses, which are extremely promising for this application. However, most high-performance halide perovskites are unstable in liquid electrolytes due to solvent intercalation. We have stabilized the Ruddlesden-Popper 2D perovskites by introducing an ion-transporting membrane separator between the thin film and a quasi-solid-state gel electrolyte interface. Here, we demonstrate an electrolyte-gated three-terminal device that operates as a switchable OR, AND, and a universal NOR gate, with one input being electrical and the other being optical, based on negative, zero, and positive gate voltages, respectively. We also demonstrated all electrical XOR gates, electrical and optical NOT, and BUFFER gates using the same. Overall, this work will open new opportunities for halide perovskites and contribute to a deeper understanding of their photophysical properties.

Indoor photovoltaics (IPVs) using low-toxicity bismuth-based perovskite-inspired materials (PIMs) can potentially power the growing number of Internet of Things devices sustainably. However, modest indoor power conversion efficiency (PCE) values are reported due to intrinsic limitations of PIMs, particularly regarding charge carrier separation and transport. Herein, polycrystalline Cs2AgBi2I9 thin films are developed with high phase purity and study their fundamental structural and photophysical properties. The comprehensive experimental and computational study reveals unique optoelectronic properties of Cs2AgBi2I9 compared to other bismuth-containing PIMs, including weak electron-phonon coupling and low exciton binding energy (40 meV). This study also demonstrates the feasibility of large and highly mobile polaron formation in Cs2AgBi2I9, supported by the observation of a phonon bottleneck and a delayed hot carrier lifetime of over 200 ps, which suggests enhanced defect tolerance and transport properties. Motivated by the suitable bandgap of this absorber (1.78 eV), the first Cs2AgBi2I9-based IPVs are developed, achieving a PCE of approximate to 8% at 1000 lux. Notably, the devices maintain high performance across various indoor environments with white LED color temperatures ranging from 2700 to 6500 K. The calculated theoretical PCE limit of >40% and the promising operational stability position Cs2AgBi2I9 as one of the most intriguing candidates for sustainable IPVs.

Organic electrochemical transistors (OECTs) are one of the most versatile electronic devices, offering great potential applications from bioelectronics and smart sensors to analog neuromorphic computing, owing to their unique electronic-ionic coupling characteristics. However, despite their considerable success, the complex interplay between electronic and ionic charge carriers leads to various anomalous device behaviors that are still poorly understood, hindering their practical application. For instance, OECTs often exhibit different hysteresis behaviors in their transfer characteristics and asymmetry in switching during turn-on and turn-off operations. Herein, the evolution of hysteresis in the transfer curves of OECTs as a function of delay time and channel length is systematically investigated, employing a range of electrochemical measurements. The findings reveal that the transition from regular hysteresis to inverted hysteresis is governed by the interplay between ion injection and extraction dynamics, which is closely linked to the open circuit potential (OCP) of the electrolyte-semiconductor interface. This work provides valuable electrochemical insights into the device physics of OECTs, paving the way for future optimization and advancement of these devices for practical implications.

The introduction of heterovalent metal ion doping in the lead (Pb) halide perovskites presents a novel opportunity to manipulate the electronic and ionic properties by introducing dopant charges and increasing the carrier concentration in single crystals. While previous studies have reported on the use of bismuth (Bi3+) doping in methylammonium lead tribromide (MAPbBr3) to adjust the optical properties, the comprehensive impact of Bi3+ doping on the structural and electronic properties of MAPbBr3 single crystals remains unexplored. This research, therefore, delves into the anomalous behavior of the structural, optical, and electrical properties of pristine and doped MAPbBr3 single crystals through a combination of experimental and computational studies. The results reveal that Bi3+ doping at the B-site of MAPbBr3 single crystals induces lead vacancies (VPb2-) and other cation vacancies near the Ag electrode interface. Moreover, bias-dependent electrochemical impedance spectroscopy measurements on the doped single crystals demonstrate a low-frequency semicircle and high-frequency recombination resistance, indicating improved ion transport properties due to Bi3+ doping. This leads to low-frequency negative capacitance, particularly in low-field regimes, due to ion accumulation at the perovskite/electrode interface. As the voltage increases, a transition from negative to positive capacitance is observed around 0.5 V. These doped single crystals show promise for memristor applications due to their adjustable electronic and ionic conductivities, offering hope for future advancements in neuromorphic computing.

Achieving high efficiency and long-term stability is crucial for advancing the commercial viability of perovskite solar cells (PSCs). Overcoming challenges related to recombination losses from surface defects and voltage losses, particularly at the perovskite/hole-transport layer interface, remains imperative. This study addressed these issues by employing a facile surface modification approach with inorganic 2D semi-metallic nanoparticles (SMNPs) of NbSe2 and NbS2 to passivate surface defects in perovskite films. The presence of divalent anions in these 2D SMNPs effectively mitigated recombination by establishing strong coordination, significantly reducing surface trap densities and enhancing the perovskite film's charge lifetime. Additionally, the divalent anions (Se2and S2-) facilitated hydrogen bond-like interactions between organic cations and 2D SMNPs. The optimized PSCs incorporating NbSe2 NP passivation exhibited exceptional performance with a remarkable power conversion efficiency of 23.03 %, an open-circuit voltage (Voc) of 1.14 V, and an outstanding fill factor exceeding 84 %, coupled with significantly improved stability. This represents one of the highest reported efficiencies for solar cells based on methylammonium cation systems. The findings of this work present an effective strategy for designing inorganic passivators to enhance the efficiency and stability of PSCs, offering valuable insights for broad applications in the field.

Indoor photovoltaics (IPVs) using low-toxicity bismuth-based perovskite-inspired materials (PIMs) can potentially power the growing number of Internet of Things devices sustainably. However, modest indoor power conversion efficiency (PCE) values are reported due to intrinsic limitations of PIMs, particularly regarding charge carrier separation and transport. Herein, polycrystalline Cs₂AgBi₂I₉ thin films are developed with high phase purity and study their fundamental structural and photophysical properties. The comprehensive experimental and computational study reveals unique optoelectronic properties of Cs₂AgBi₂I₉ compared to other bismuth-containing PIMs, including weak electron-phonon coupling and low exciton binding energy (40 meV). This study also demonstrates the feasibility of large and highly mobile polaron formation in Cs₂AgBi₂I₉, supported by the observation of a phonon bottleneck and a delayed hot carrier lifetime of over 200 ps, which suggests enhanced defect tolerance and transport properties. Motivated by the suitable bandgap of this absorber (1.78 eV), the first Cs₂AgBi₂I₉-based IPVs are developed, achieving a PCE of ≈8% at 1000 lux. Notably, the devices maintain high performance across various indoor environments with white LED color temperatures ranging from 2700 to 6500 K. The calculated theoretical PCE limit of >40% and the promising operational stability position Cs₂AgBi₂I₉ as one of the most intriguing candidates for sustainable IPVs.

Perovskite-inspired materials are a new class of semiconductors to address several challenges faced by lead-based halide perovskites. These lead-free halide perovskites potentially eliminate the lead toxicity and improve the stability under operating conditions. However, a lack of understanding of the photophysical and electronic properties of these materials prevents further progress. Here, the effect of cooling rate on defect formation in lead-free Cs3Bi2Br9 single crystals has been investigated. The crystal synthesized under controlled cooling shows reduced trap density. High-resolution transmission electron microscopy image analysis of these materials reveals that the perovskite crystals synthesized from the controlled-cooling method does not show the presence of point defects or dislocations, while naturally cooled perovskite crystals have both point defects and dislocations, increasing grain resistivity by an order of magnitude, as supported by electrochemical impedance spectroscopy. Furthermore, contact angle measurements show that the film obtained via controlled cooling exhibits greater surface hydrophobicity, indicating enhanced stability. Cyclic voltammetry measurements of the fabricated thin film-based monolithic photo-supercapacitor under illumination show that devices based on naturally cooled perovskites exhibit only 40% enhancement in photo-capacitance. In contrast, devices fabricated from controlled-cooled perovskites exhibit a photo-capacitance enhancement of over 130% at a scan rate of 140 mV s-1.

Perovskite-inspired materials (PIMs) are gaining increasing attention among emerging photovoltaic absorbers due to their inherent air stability and low-toxicity potential. However, operational stability, the Achille’s heel of all emerging photovoltaics, has been largely overlooked in PIMs research so far, making it difficult to forecast their practical use in real- world applications. In this work, we analyse the operational stability of a promising new PIM composition, CsMAFA-Sb:Bi, generated through the antimony:bismuth co-alloying of a triple cation vacancy-ordered antimony-based PIM. Through an in-depth theoretical and experimental investigation, we demonstrate that the co-alloying induces local structural changes that lead to enhanced microstructure, reduced trap-assisted recombination, and increased solar cell power conversion efficiency (PCE), with the highest value being 3.05%. Accelerated aging tests according to ISOS L-1 and L-2 protocols highlight the crucial role of co-alloying in enhancing stability. Specifically, maximum power point tracking at 85 °C shows a projected T80 lifetime of 275 hours for CsMAFA-Sb:Bi devices, which has never been achieved not only for any other PIM-based device but also for high-efficiency technologies, such as lead halide perovskite solar cells with similar device constituents. This work encourages future studies on PIM-based photovoltaics for their potential operational stability, with the goal of reducing the performance gap with established technologies.

The growth of hybrid halide perovskite single crystals has gathered significant attention due to their low trap density and fewer defects, which make them promising candidates for enhancing the performance of optoelectronic devices. However, in this work, we have explored the potential advantages of defects and vacancies in lead-free perovskites, specifically for applications in CO2 reduction and energy storage. We have synthesized vacancy-ordered lead-free perovskite single crystals, Cs3Bi2Br9 and Cs3Bi2Cl9, using a fast-cooling process before grinding them to prepare a nanocrystalline powder. This method deviating from the traditional slow cooling process, creates more defects and vacancies in these nanomaterials. Interestingly, these defects, often viewed as detrimental in most optoelectronic applications, have proven beneficial for energy storage in our study. During the fast-cooling process, CO, C–O, and O–Bi–O bonds are formed in both halide perovskites indicating adsorption and formation of products. Therefore, these materials could be used in CO2 reduction without the use of a metal-organic framework. These bonds are found to be absent in defect-free perovskites produced by the traditional slow cooling process. Furthermore, the specific energy density of supercapacitors fabricated from these nanocrystalline materials is increased by 15–20 % compared to the traditional slow-cooling perovskite materials. This enhancement in energy density underscores the potential of these vacancy-rich perovskite materials in developing supercapacitors with better storage performance. Overall, this work shows how defects and vacancies engineering in lead-free halide perovskite's single crystal growth can be used to create new opportunities for their use in energy storage and CO2 reduction technologies.

Owing to the exceptional photovoltaic and optoelectronic properties of metal halide perovskites, they have sparked an intensive interest in the research community. CsPbBr3 perovskite nanocrystals (NCs) have come into sight due to their versatile properties that can be achieved through structural modification. While the prior research on perovskite nanocrystals has focused mainly on tuning optical and electronic properties, the understanding of their electronic-ionic kinetics still remains a significant research gap. In this work, we explore how the size of CsPbBr3 NCs impacts their electronic-ionic properties by using electrochemical impedance spectroscopy (EIS). We systematically tune NC size and investigate the resulting dielectric properties, conductivity, and capacitance. Notably, larger NCs exhibit anomalous behavior similar to that of perovskite polycrystalline thin films in the range of 0.4-0.6 V, indicating strong electronic-ionic coupling. Conversely, smaller NCs display weak electronic-ionic coupling due to ion localization. Additionally, this study sheds light on the electronic-ionic behavior of NCs approaching quantum confinement with a size reduction, suggesting opportunities for defect engineering. Ultimately, this work will pave the way for developing advanced electronic devices utilizing perovskite nanocrystals.

Hybrid halide perovskites (HHPs) have revolutionized the field of solar cells due to their low cost, solution-processable synthesis, and exceptional device performance. Although lead (Pb)-based perovskites are currently the most efficient, their application in indoor photovoltaics and wearable electronics is limited by lead's toxicity. This has intensified the search for Pb-free alternatives, particularly for use in portable electronic devices. In this study, we utilized a vapor-assisted solution process to systematically engineer the composition of bismuth-based perovskite-inspired materials (PIMs) through indium doping, forming homogeneous and pinhole-free (CH3NH3)(3)Bi2-xInxI9 (Bi-In) films. These bimetallic Bi-In perovskites exhibit enhanced properties, including high recombination resistance, reduced low-frequency capacitance, lower defect density, and minimal microstrain. Electrochemical impedance spectroscopy (EIS) shows significantly reduced ion migration in Bi-In compositions compared with pure bismuth-based counterparts. The optimized Bi-In-based solar cells achieved a power conversion efficiency (PCE) of 2.5% under outdoor illumination and 5.9% under indoor lighting, showcasing their potential as promising lead-free alternatives for photovoltaic applications.

Hybrid halide perovskites have been the materials of the decade as tremendous progress has been observed in perovskite solar cells, perovskite light-emitting diodes, perovskite-based detectors, field effect transistors, and memristor applications. The mixed ionic-electronic conductance characteristic of these materials is one of the most exciting and mysterious processes for the next generation of optoelectronic devices. The primary concern in these perovskite-based optoelectronic devices is an understanding of charge carrier dynamics in the presence of ionic transport. While the theoretical charge carrier mobility in halide perovskites is very high, the experimental values are 2 to 3 orders of magnitude lower than the theoretical value due to strong electron-ion coupling. Also, photoinduced and field-induced ion migrations are the major bottlenecks for the commercialization of perovskite-based optoelectronic devices as they degrade under operating conditions. Therefore, the decoupling of electronic-ionic transport in perovskites may improve the overall charge carrier mobility and device stability. However, ion migration could be beneficial to use in other smart technologies, such as reconfigurable resistive switches for neuromorphic computing, electrolyte-gated electrochemical transistors, photoelectrolysis, and photorechargeable energy storage for next-generation smart portable electronic devices. In this review, we have discussed iontronics in hybrid halide perovskite materials and their applications and challenges in various smart portable electronic devices, including, electrolyte-gated electrochemical transistors, memristors, photorechargeable ion capacitors, photocatalysis, and CO2 reduction.