On interface recombination, series resistance, and absorber diffusion length in BiI3 solar cells

Bismuth triiodide is a lead-free direct wide-bandgap solution-processable semiconductor that could be an alternative to lead-based perovskites in tandem or multijunction solar cells. However, the power conversion efficiency of single-junction BiI3 solar cells remains low. Here, we determine the main loss mechanisms of BiI3 solar cells in both n-i-p and p-i-n architectures. Overall, p-i-n devices have higher power conversion efficiency than that of n-i-p. It is found that n-i-p devices have higher (and significant) non-radiative recombination at the interface of the BiI3/transport layer, resulting in a lower open-circuit voltage than p-i-n devices. Moreover, the high series resistance (>70 Ω cm2) and a low average electron–hole diffusion length (∼60 nm) contributes to the low short-circuit current density (