Enhancing carrier transport in Cs2AgBiBr6 double perovskites through multifunctional ferroelectric polymer doping

Cs2AgBiBr6 lead-free double perovskites are promising materials for optoelectronic applications but suffer from limited carrier transport due to defects and strong electron–phonon coupling. In this work, we introduce a multifunctional doping strategy using the ferroelectric polymer polyvinylidene fluoride (PVDF) to simultaneously address these challenges. PVDF modulates film crystallization to reduce defects, relaxes lattice strain to weaken electron–phonon coupling, and—after electrical polarization—provides a built-in electric field that promotes charge separation. As a result, PVDF-doped Cs2AgBiBr6 solar cells achieve a champion power conversion efficiency of 1.91%, representing a 40% improvement over the control device (1.36%), with much improved stability. This work presents a simple and effective approach to improving carrier dynamics in double perovskites for broader optoelectronic applications.