Effect of alloying on the carrier dynamics in high-performance perovskite solar cells

High-efficiency solar cells often require light absorbers prepared from alloys, such as Cd Te_(1-x)Se_(x),CuIn_(x)Ga_(1-x)Se_(2), Cu_(2)ZnSnS_(4-x)Se_(x), and(Cs_(x)FA_(1-x))Pb(I_(1-y)Br_(y))_(3). However, how alloying affects solar cell performance is poorly understood, and determining common features associated with alloying is of significant interest. Herein, we studied the correlation between the A/X site compositional ratio and the photogenerated carrier dynamics using mixed halide perovskites(Cs_(x)FA_(1-x))Pb(I_(1-y)Br_(y))_(3)as examples.Nonadiabatic molecular dynamics calculations demonstrated that charge carrier recombination is highly sensitive to the compositional ratio at the A/X-site. The enhanced lifetime is attributable to the suppression of atomic fluctuations, the weakening of electron-phonon coupling, and a reduction in the electrontransition probability between band edges. The optimal Br concentration was determined to be ~18%, in agreement with experimental observations. This study not only advances our understanding of why mixed perovskites usually exhibit superior experimental photoelectric properties, but also provides a route for optimizing the carrier lifetimes and efficiencies of perovskite solar cells.