ABSTRACT Lead‐free perovskite solar cells (PSCs) have emerged as sustainable alternatives to toxic lead‐based counterparts, offering environmental compatibility and tunable optoelectronic properties. However, achieving long‐term stability remains a major bottleneck hindering commercialization. Among lead‐free systems, tin‐based perovskites have received the greatest attention owing to their structural and electronic similarity to Pb‐based analogs and their potential for high efficiencies, yet they remain limited by intrinsic Sn 2 + oxidation, ion migration, and rapid degradation under ambient conditions. In contrast, antimony‐, bismuth‐, and germanium‐based perovskites exhibit superior chemical and environmental stability but suffer from wide bandgaps, localized electronic states, and low carrier mobility, resulting in modest power conversion efficiencies. This review provides a comprehensive, stability‐centered analysis of lead‐free PSCs, emphasizing intrinsic degradation mechanisms, extrinsic stress factors, and the role of fabrication, interfacial, and additive engineering in improving device stability. Advanced in‐situ and operando characterization techniques are discussed to elucidate defect dynamics and degradation pathways. While Sn‐based systems are analyzed in greater detail due to the availability and depth of mechanistic studies, equal attention is given to recent developments in Bi‐, Sb‐, and Ge‐based perovskites to present a balanced perspective. Finally, key challenges, mitigation strategies, and future research directions are outlined to guide the design of stable, efficient, and environmentally benign lead‐free perovskite photovoltaics.

Visible Light Communication (VLC) is an attractive complement to Radio Frequency (RF) for Internet of Things (IoT) deployments, as it can reuse existing lighting infrastructure and avoid electromagnetic interference. However, enabling color shift keying (CSK) with solar-cell receivers remains challenging because conventional silicon solar cells exhibit broadband spectral responses and cannot reliably separate RGB components without optical filters, which reduce harvested energy and increase system complexity. We present Helios-CSK, a solar-based CSK receiver that enables filter-free color discrimination by leveraging an array of commercial off-the-shelf multi-material solar cells with complementary spectral responses. To address strong channel variability caused by changes in distance and ambient illumination, Helios-CSK performs end-to-end decoding using a bidirectional Long Short-Term Memory (LSTM) network trained on anchor-referenced differential features derived from anchor symbols embedded in each packet. A prototype implementation with seven solar cells demonstrates robust CSK decoding across varying distances and lighting conditions, achieving reliable communication at data rates of up to 2 kb/s over distances of up to 45 cm while significantly reducing bit error rate compared to conventional channel-estimation-based decoding. Helios-CSK highlights a practical path toward low-power and maintenance-free IoT links, with future potential for self-sustaining operation when integrated with dedicated harvesting circuitry.

Perovskite solar cells (PSCs) are revolutionizing the field of renewable energy (RE) production due to their extraordinary PV responses and affordable large-scale production. It has garnered significant curiosity owing to its distinctive features, including as enhanced light harvesting, carrier transport, and relatively simple production. In this regard, Hybrid organic-inorganic perovskites (HOIP) are attracting considerable interest as photon harvesters in PV cells because of their substantial improvements in power conversion efficiency (PCE). This article fundamentally addresses the PV performances, PCEs, short and long-term stability issues, and practical challenges and benefits associated with the Caesium (Cs) incorporation into the HOIP mono- and mixed-halide solar cells. Additionally, we have analysed the material characterises, device physics, fabrication processes and the underlying degradation mechanisms of Cs-HOIP structures, focusing on the device optimization for ensuring enhanced stability and efficiency as well as improved electrical performances. Finally, we have offered insights on the future commercialization trajectory for large-area Cs-HOIP PSCs, emphasizing the significance of improved stability and better efficiency with convenient fabrication processes for the broad acceptance of this promising technology. This review thoroughly examines high-efficiency HOIP solar cells, emphasizing essential elements such device designs, fabrication methods, solvent engineering and defect passivation, as well as recent developments and challenges.

Three-dimensional and two-dimensional perovskite solar cells are becoming popular due to their simultaneous improvements in efficiency and stability. The deposition of long aliphatic or bulky aromatic ammonium halide precursors promotes the formation of a quasi-two-dimensional perovskite layer on top of the three-dimensional perovskite. This quasi-two-dimensional layer serves two leading roles: passivation, which enhances efficiency, and capping, which maintains stability. A thorough comparison of the passivation effects of aliphatic and aromatic organic precursors on the performance of perovskite solar cells is scarce in the literature. Additionally, studies on the passivation effects of mixed aliphatic and aromatic organic precursors are limited. In this work, tert-octylammonium chloride/bromide is used as an aliphatic organic precursor, while methoxyphenethylammonium chloride/bromide is selected as an aromatic organic precursor. We achieved an excellent device using a mixed passivation strategy comprising 70 % methoxy-phenethylammonium chloride and 30 % tert-octylammonium bromide. The device demonstrates a power conversion efficiency of around 22 % and retains approximately 96 % of its initial efficiency after 1000 h.

Three-dimensional/two-dimensional bilayered perovskite solar cells have recently become popular for ensuring high efficiency and promising long-term stability. The 3D/2D bilayered perovskite thin film is mainly used in regular (n-i-p)-type perovskite solar cells. In this review, our discussion also focuses on the regular kind of perovskite solar cells. In a 3D/2D bilayered perovskite thin film, the 2D perovskite layer works as a capping layer on top of the 3D perovskite thin film. The 2D capping layer heals the surface and bulk defects of the 3D perovskite thin film. The 2D layer interfaces between the 3D perovskite and hole transport layers. The 2D layer also acts as a shield against moisture and heat. This layer also inhibits ion migration between layers (3D perovskite and back contact). This review lists and investigates different organic precursors deposited as a 2D capping layer on top of the 3D perovskite thin film to explore their impact on the solar cell’s efficiency and stability. The possible challenges and remedies in growing a 2D capping layer on top of the 3D perovskite thin film are also discussed.

Visible Light Communication (VLC) provides an energy-efficient wireless solution by using existing LED-based illumination for high-speed data transmissions. Although solar cells offer the advantage of simultaneous energy harvesting and data reception, their broadband nature hinders accurate decoding of color-coded signals like Color Shift Keying (CSK). In this paper, we propose a novel approach exploiting the concept of tandem solar cells, multi-layer devices with partial wavelength selectivity, to capture coarse color information without resorting to energy-limiting color filters. To address the residual spectral overlap, we develop a bidirectional LSTM-based machine learning framework that infers channel characteristics by comparing solar cells' photovoltaic signals with pilot-based anchor data. Our commercial off-the-shelf (COTS) solar prototype achieves robust performance across varying distances and ambient lighting levels, significantly reducing bit error rates compared to conventional channel estimation methods. These findings mark a step toward sustainable, high-performance VLC systems powered by the multi-layer solar technologies.

2-dimensional (2D) materials are gaining immense popularity as interface passivation films for perovskite solar cells (PSCs). Among several types of interface passivation films used, long carbon chain alkylammonium bromides are the commonly used option due to their availability, cost, and easy deposition method. These 2D films passivate the boundaries of the cells, but a lengthy carbon chain can affect the carrier conduction in the device. Here, we have optimized the carbon chain length in 2D alkylammonium bromide films, giving the best-performing PV devices. All the 2D passivation films improved the open circuit voltages and fill factors of the devices. The champion cell obtained using n-hexylammonium bromide 2D film showed a power conversion efficiency (PCE) of 21.4%, a 12.6% increase from the control device. Moreover, all the passivated devices were considerably more stable in storage and operational conditions. Surface analysis with atomic force microscopy and scanning electron microscopy showed smoother surfaces with larger grains when 2D passivation films were added. In addition, depth profile measurements showed lower ion migration in the passivated films, directly resulting in mitigating hysteresis in the device in the long term. Overall, adding an optimized 2D passivation film can greatly improve PSCs with minimal extra cost and processing time.

Previous reports have revealed that by leveraging solid additives, organic solar cells (OSCs) can surpass the device's performance beyond the intrinsic limitations of host photoactive molecules, a remarkable advancement. However, the impacts of more complex interactions introduced by solid additives are not yet well understood. Herein, optimizing the fabrication process based on the traditional efficiency-guided approach fails to represent the ideal and most practical devices. In particular, achieving superior operational stability while minimizing the device performance scattering was found to require processing solvent evaporation to be synchronized with the volatility of the chosen solid additive. However, this may be challenging since most organic photoactive materials display excellent efficiencies only with selected solvents. Accordingly, this work also demonstrates the potential of dual and complementary solvents selection, consisting of low boiling point (primary) and high boiling point (secondary). This strategy allows for the suppression of any potential trade-offs in efficiency. Meanwhile, the operational stability and precision of device performance are substantially enhanced. Additionally, solid additives have demonstrated that the singlet exciton dissociation rate does not limit the free charge generation yield. Overall, these findings are expected to reformulate OSC device fabrication strategies towards more practical devices.

There has been rapid and continuous development in organic semiconductors for photovoltaics over the past decade, and power conversion efficiencies ( PCEs ) of nearly 21 % have already been achieved. Organic semiconductors not only offer competitive PCEs but also semitransparency, color tunability, lightweight, solution-processability, mechanical stretchability, synthetic flexibility, and most importantly, biocompatibility. This combination of properties opens up a range of unconventional applications beyond traditional solar farms, which include building-integrated installations, smart windows, agrivoltaics, indoor photovoltaics, wearable electronics, and thermoregulatory devices. Hence, initial impressions toward commercial feasibility that are conventionally based on traditional photovoltaic applications could be misleading. This review highlights that organic semiconductors may have already surpassed existing photovoltaic materials in certain types of utilization. Accordingly, the core ideas of emerging unconventional photovoltaic applications, their latest developments, current challenges, and key performance factors beyond PCEs are covered herein. Overall, this mini-review provides practical perspectives, driving more research attention toward other more up-to-date photovoltaic applications with modern technologies and architectural motifs.

Due to the radius mismatch between iodine and chlorine, ion migration is unavoidable in chloride-iodide perovskites. The presence of atomic vacancies in the solution-processed perovskite thin film works as a route of ion migration. Here, we investigate the consequence of the ion migration in chloride-iodide perovskite solar cells. We use FA0.6MA0.4PbI2.7Cl0.3 as the active perovskite layer. We passivate the top surface of the chloride-iodide perovskite thin film with mixed 4-fluorobenzylammonium chloride and 4-fluorobenzylammonium bromide. We observe that fluorinated benzylammonium halides show better passivation and hydrophobicity. Compared to the non-passivated solar cells, we get a significant fill factor and stability improvement. We get 76.44% fill factor from our passivated solar cell. Besides, our passivated solar cell offers a photo conversion efficiency of 21.10%. Moreover, we also get about 80% stability without encapsulation after 56 days.

Salinity intrusion in the coastal regions of Bangladesh is particularly challenging for communities living near mangrove forests, which have salinity-dependent ecosystems. The salinity levels within groundwater aquifer systems here vary seasonally, and vegetation has the potential to serve as a mitigation strategy to reduce salinity intrusion. In this study, we focused on the southwest coastal region of Bangladesh, an area characterized by high salinity intrusion. We analyzed groundwater samples collected from monitoring wells during both dry and wet seasons. Additionally, we recorded the necessary physical and chemical parameters to support the analysis. We explored several GIS interpolation methods, including Inverse Distance Weight (IDW), Empirical Bayesian Kriging (EBK), and Kernel interpolation to map salinity while employing remote sensing techniques to map vegetation dynamics. We used spatial regression and bivariate clustering methods to identify and map the seasonal spatial dependence variation of salinity and vegetation. Our analysis indicates a negative linear relationship between salinity and vegetation dynamics, with the correlation being notably stronger in the dry season (Pearson correlation − 0.540) compared to the wet season (Pearson correlation − 0.149). The spatial regression model indicated spatial dependence between these two variables only during the dry season, with an R-squared value of 0.972. Bivariate clustering results identified approximately 20

The morphology of the active layer mostly affects the photovoltaic efficiency of organic solar cells (OSCs).

Organic solar cells (OSCs) are becoming increasingly popular in the scientific community because of their many desirable properties. These features include solution processability, low weight, low cost, and the ability to process on a wide scale using roll-to-roll technology. Enhancing the efficiency of photovoltaic systems, particularly high-performance OSCs, requires study into not only material design but also interface engineering. This study demonstrated that two different types of OSCs based on the PTB7-Th:IEICO-4F and PM6:Y6 active layers use a ZnO bilayer electron transport layer (ETL). The ZnO bilayer ETL comprises a ZnO nanoparticle (ZnO NP) and a ZnO layer created from a sol-gel. The effect of incorporating ZnO NPs into the electron transport layer (ETL) was studied; in particular, the effects on the electrical, optical, and morphological properties of the initial ZnO ETL were analyzed. The ability of ZnO films to carry charges is improved by the addition of ZnO nanoparticles (NPs), which increase their conductivity. The bilayer structure had better crystallinity and a smoother film surface than the single-layer sol-gel ZnO ETL. This led to a consistent and strong interfacial connection between the photoactive layer and the electron transport layer (ETL). Therefore, inverted organic solar cells (OSCs) with PTB7-Th:IEICO-4F and PM6:Y6 as photoactive layers exhibit improved power conversion efficiency and other photovoltaic properties when using the bilayer technique.

The phenomenon of the self‐formation of a passivation layer at the interface of the perovskite/electron‐transport layer (ETL) is observed. FA0.6MA0.4PbI3−xClx perovskite thin film is deposited on a SnO2 nanoparticle thin‐film ETL. It is observed from the depth‐resolved spectroscopy that the Sn2+ ion migrates toward the perovskite layer within the ETL. At the same time, Cl− ion also migrates toward ETL within the perovskite layer. This unique ion migration phenomenon leads us to conclude that a passivating SnCl2 layer is formed at the perovskite/ETL interface. It is found that this SnCl2 layer at the interface works as a passivation layer like Al2O3. There is a significant effect of this self‐formed passivating layer behind the improvement of the device's efficiency and stability. It is believed that this SnCl2 passivation layer helps to reduce the recombination loss at the interface and boosts the performance of the perovskite solar cell (PSC). The perovskite/hole‐transport layer is also passivated with octylammonium bromide. Finally, the PSC offers a photoconversion efficiency (PCE) of 20.81% under 1 sun and AM1.5 G condition. Again, it maintains more than 80% of PCE under open‐air room conditions, white light emitting diode, and 85 °C continuous heating for more than 12 h without encapsulation.

Lead halide perovskite solar cells (PSCs) have achieved remarkable efficiencies comparable to those of their established silicon counterparts at a very fast pace. Moreover, solution-processable facile technologies offer low-cost, low-temperature, scalable fabrication of these solar cells. Numerous studies have focused on improving the performance, stability, and processing of PSCs. However, potential lead toxicity and poor long-term stability impede their commercialization. In recent years, several studies have developed novel encapsulants for PSCs that can simultaneously improve stability and impede potential lead leakage. Although improvements have been made on both fronts, no solution to date could achieve a level of stability and leakage prevention that could result in a market breakthrough. Here, we analyze PSC encapsulation and lead leakage prevention techniques undertaken in recent years. While most of the related studies focused on improving either stability or toxicity, we note that both can be solved together with a suitable encapsulant that is impermeable to both moisture and Pb2+ ions. In addition, the lack of a unified standard stability testing protocol has led to stability testing under a variety of temperatures, humidities, and environmental conditions. Therefore, the urgency for a standard protocol for stability and lead toxicity testing cannot be overlooked.

Hybrid metal halide perovskite solar cells (PSCs) are the most promising candidates to share the future energy market with silicon solar cells thanks to their excellent photovoltaic (PV) properties in single junction and tandem applications. Although PSCs are already highly efficient, their performance can be further improved by passivating the perovskite boundaries and improving current-voltage hysteresis. Here, we implement a double-sided passivation approach to enhance the perfor-mance of n-i-p structured PSCs, showing how passivating on either side improves cell performance. The electron-collecting side was passivated with biphenyl-4,4-dicarboxylic acid (BPDC), and n-octyl ammonium bromide was used to passivate the hole-collecting side. The power conversion efficiency of the champion cell improved from 18.7 % for control to 20.9 % when double-sided passivation was implemented. Surface imaging showed how the surface boundaries improved following passivation, resulting in better open circuit voltages (VOC) and fill factors. In addition, passivation creates a barrier for ion migration, improving J-V hysteresis and stability in the process. The champion cell displayed a VOC of 1192 mV with double-sided passivation, incurring only-390 mV loss, thereby achieving a high VOC with a mid-bandgap perovskite. Preliminary degradation testing in ambient conditions shows that double-sided passivation also improves the stability of the cells by impeding ion migration.