Selenium-Diffusional Precursor Engineering for High-Efficiency CdSeTe Solar Cells with 80% Fill Factor

Graded CdSeTe absorbers offer a promising route to surpass the efficiency limits of conventional CdTe solar cells, but device performance remains highly sensitive to the properties of the Se-diffusional precursor. Here, a precursor-management strategy is introduced that incorporates oxygen and chlorine during CdSe precursor processing to optimize Se diffusion and crystallization. This treatment improves the CdSeTe absorber microstructure, suppresses buried interfacial voids, and diminishes surface-potential fluctuations, thereby lowering interfacial recombination and enhancing carrier collection. Devices fabricated with this approach deliver a champion power conversion efficiency of 20.6% (V_OC = 859 mV, J_SC = 29.9 mA cm^-2, FF = 80.0%), underscoring the critical role of precursor chemistry in advancing graded-absorber photovoltaics.