Being an important green quantum dot (QD), AgInS2 (AIS) has been used as sensitizers for QD sensitized solar cells (QDSCs) but with low power conversion efficiency (PCE). Herein, we have used oleylamine as surfactant to synthesize AIS and quaternary Zn-Ag-In-S (ZAIS) QDs via a facile and green method. The assembled AIS QDSCs show high PCE of 2.46%. After doping with Zn to form ZAIS QDs, the defect states have been modified, resulting in the enhanced photoluminescence. The assembled ZAIS QDSCs receive the greatly enhanced PCE of 4.50% with dramatically increased current density. Various characterizations verify that the high quality of QDs, large recombination resistance at QD/electrolyte interface, high photon to electron conversion efficiency and longer electron life are contributed by the tuned intrinsic defects which are strongly related with synthesis and composition, finally leading to the high performance of photovoltaic devices. (C) 2019 Elsevier Inc. All rights reserved.