Synergistic doping of fullerene electron transport layer and colloidal quantum dot solids enhances solar cell performance.

The spatial location of the predominant source of performance-limiting recombination in today's best colloidal quantum dot (CQD) cells is identified, pinpointing the TiO2: CQD junction; then, a highly n-doped PCBM layer is introduced at the CQD: TiO2 heterointerface. An n-doped PCBM layer is essential to maintain the depletion region and allow for efficient current extraction, thereby producing a record 8.9% in overall power conversion efficiency.