Quaternary quantum dots with gradient valence band for all-inorganic perovskite solar cells.

The severe interface charge recombination caused by the large energy difference between perovskite material and carbon electrode significantly limits the further performance improvement of the all-inorganic perovskite solar cells (PSCs). We apply innovatively multilayer of quaternary Ag-In-Ga-S (AIGS) quantum dots (QDs) with cascade-like valence bands as hole-transport materials to assemble all-inorganic PSCs, and the resultant all-inorganic PSCs exhibit a power conversion efficiency (PCE) of 8.46%, which is enhanced by 20.9% in comparison with 7% for the pristine device. The high performance of the PSCs indicates that sequential layers of AIGS QDs with cascade-like energy levels can facilitate the charge separation, reduce the barrier the holes crossing and suppress the charge recombination. Stack of QDs with cascade-like energy levels provide solution-processed PSCs with a new method to enhance device performance.