Niranjana Mohan Kumar

Improvements to the radiative efficiency of halide perovskite thin films are necessary to approach fundamental solar cell performance limits. We tailored perovskite crystallization by leveraging the eutectic interaction between zinc bromide and methylammonium chloride additives. The resulting films had high photoluminescence quantum yield and charge carrier decay times and low surface recombination velocity. Nanoprobe x-ray microscopy revealed local melting of the eutectic at grain boundaries during annealing that reduced intragranular structural defect density. Annealing also homogenized the halide distribution and caused zinc segregation to grain boundaries. Solar cells fabricated with the volatile eutectic reached 26.5% power conversion efficiency (PCE, certified 25.9%), and perovskite minimodules (areas more than 15 square centimeters) had 23.9% PCE. Small-area cells with a poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] hole transporter retained 85.8% of their initial 24.1% PCE after 1400 hours of continuous operation at 85°C. Furthermore, this approach enables 26.1% external quantum efficiency as light-emitting diodes.

Selenium grading plays a critical role in state‐of‐the‐art Cadmium Telluride photovoltaic cells by enhancing long‐wavelength absorption and extending minority carrier lifetimes —key to enabling the current performance record of 23.08%. However, very little is understood about selenium motion. In this study, a comprehensive, multimodal, and multiscale approach is employed to investigate Se migration and local structural changes in copper (Cu)‐doped CdSeTe solar cells subjected to accelerated stress. X‐ray fluorescence (XRF) microscopy shows unexpected levels of Se diffusion after 500 h under heat (75°C) and light (0.8 suns, 80 mW / cm ² ), suggesting the coexistence of fast and slow diffusion channels even at low temperatures, with unexpectedly low activation energies (<0.85 eV). X‐ray Absorption Near Edge Structure (XANES) analysis indicates a preferential migration of Se atoms to anionic lattice sites and a reduction in Se‐Cl co‐passivation at Te‐terminated dislocation cores. These findings point to a reconfiguration of Se local environments and highlight the potential role of extended structural defects in enabling Se transport at low temperatures. Additionally, XANES results suggest that the presence of metallic Cu across the absorber layer may contribute to back‐contact degradation and reduced hole density in both fresh and aged devices.