14.31% Power Conversion Efficiency of Sn-Based Perovskite Solar Cells via Efficient Reduction of Sn 4

Colloidal Zeta Potential Modulation as a Handle to Control the Crystallization Kinetics of Tin Halide Perovskites for Photovoltaic Applications

Tin halide perovskites (THPs) have demonstrated exceptional potential for various applications owing to their low toxicity and excellent optoelectronic properties. However, the crystallization kinetics of THPs are less controllable than its lead counterpart because of the higher Lewis acidity of Sn2+, leading to THP films with poor morphology and rampant defects. Here, a colloidal zeta potential modulation approach is developed to improve the crystallization kinetics of THP films inspired by the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. After adding 3-aminopyrrolidine dihydro iodate (APDI2) in the precursor solution to change the zeta potential of the pristine colloids, the total interaction potential energy between colloidal particles with APDI2 could be controllably reduced, resulting in a higher coagulation probability and a lower critical nuclei concentration. In situ laser light scattering measurements confirmed the increased nucleation rate of the THP colloids with APDI2. The resulting film with APDI2 shows a pinhole-free morphology with fewer defects, achieving an impressive efficiency of 15.13 %.

Cyano-Coordinated Tin Halide Perovskites for Wearable Health Monitoring and Weak Light Imaging

Low-toxicity tin halide perovskites with excellent optoelectronic properties are promising candidates for photodetection. However, tin halide perovskite photodetectors have suffered from high dark current owing to uncontrollable Sn2+ oxidation. Here, 2-cyanoethan-1-aminium iodide (CNI) is introduced in CH(NH2 )2 SnI3 (FASnI3 ) perovskite films to inhibit Sn2+ oxidation by the strong coordination interaction between the cyano group (C≡N) and Sn2+ . Consequently, FASnI3 -CNI films exhibit reduced nonradiative recombination and lower trap density. The self-powered photodetector based on FASnI3 -CNI exhibits low dark current (1.04 × 10-9 A cm-2 ), high detectivity (2.2 × 1013 Jones at 785 nm), fast response speed (2.62 µs), and good stability. Mechanism studies show the increase in the activation energy required for thermal emission and generated carriers, leading to a lower dark current in the FASnI3 -CNI photodetector. In addition, flexible photodetectors based on FASnI3 -CNI, exhibiting high detectivity and fast response speed, are employed in wearable electronics to monitor the human heart rate under weak light and zero bias conditions. Finally, the FASnI3 -CNI perovskite photodetectors are integrated with a 32 × 32 thin-film transistor backplane, capable of ultraweak light (170 nW cm-2 ) real-time imaging with high contrast, and zero power consumption, demonstrating the great potential for image sensor applications.

Breaking the bottleneck of lead-free perovskite solar cells through dimensionality modulation

The emerging perovskite solar cell (PSC) technology has attracted significant attention due to its superior power conversion efficiency (PCE) among the thin-film photovoltaic technologies. However, the toxicity of lead and poor stability of lead halide materials hinder their commercialization. In this case, after a decade of effort, various categories of lead-free perovskites and perovskite-like materials have been developed, including tin halide perovskites, double perovskites, defect-structured perovskites, and rudorffites. However, the performance of the corresponding devices still falls short of expectations, especially their PCE. The limitations mainly originate from either the unstable lattice structure of these materials, which causes the distortion of their octahedra, or their low dimensionality (e.g., structural and electronic dimensionality)-correlated poor carrier transport and self-trapping effect, accelerating nonradiative recombination. Therefore, understanding the relationship between the structures and performance in these emerging candidates and leveraging these insights to design or modify new lead-free perovskites is of great significance. Herein, we review the variety of dimensionalities in different categories of lead-free perovskites and perovskite-like materials and conclude that dimensionality is an important aspect among the crucial indexes that determine the performance of lead-free PSCs. In addition, we summarize the modulation of both structural and electronic dimensionality, and the corresponding enhanced optoelectronic properties in different categories. Finally, perspectives on the future development of lead-free perovskites and perovskite-like materials for photovoltaic applications are provided. We hope that this review will provide researchers with a concise overview of these emerging materials and help them leverage dimensionality to break the bottleneck in photovoltaic applications.

Enhancing Performance and Stability of Sn-Pb Perovskite Solar Cells with Oriented Phenyl-C61-Butyric Acid Methyl Ester Layer via High-Temperature Annealing

Phenyl-C61-butyric acid methyl ester (PCBM) can be used as a passivation material in perovskite solar cells (PeSCs) in order to reduce the trap site of the perovskite. Here, we show that a thick PCBM layer can form a smoother surface on the SnO2 substrate, improving the grain size and reducing the microstrain of the perovskite. High-temperature annealing treatment of PCBM layer not only increases its solvent resistance to perovskite precursor or antisolvent, but also enhances its molecular alignment, resulting in improved conductivity as an electron transport layer. High-temperature annealed PCBM (HT-PCBM) effectively minimizes trap-assisted nonradiative recombination by reducing trap density in perovskite and improving the electrical properties at the interface between SnO2 and perovskite layers. This HT-PCBM process significantly enhances the performance of the PeSCs, including the open-circuit voltage (VOC) from 0.39 to 0.77 V, fill factor from 52% to 65%, and power conversion efficiency (PCE) from 6.03% to 15.50%, representing substantial improvements compared to devices without PCBM. This PCE is the highest efficiency among conventional (n-i-p) Sn-Pb PeSCs reported to date. Moreover, passivating the trap sites of SnO2 and separating the interface between the Sn-containing perovskite and the substrate effectively have improved the stability of the Sn-Pb perovskite in the n-i-p structure. The optimized best device with HT-PCBM has maintained an efficiency of over 90% for more than 300 h at 85 °C and 5000 h at room temperature in a glovebox atmosphere.