Enhanced electron extraction capability of polymer solar cells via modifying the cathode buffer layer with inorganic quantum dots

Enhanced performance of polymer solar cells (PSCs) based on the blend of poly[N-9''-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT):[6,6]-phenyl-C-70-butyric acid methyl ester (PC71BM) is demonstrated by titanium dioxide (TiO2) interface modification via CuInS2/ZnS quantum dots (CZdots). Devices with a TiO2/CZdots composite buffer layer exhibit both a high short-circuit current density (J(sc)) and fill factor (FF), leading to a power conversion efficiency (PCE) up to 7.01%. The charge transport recombination mechanisms are investigated by an impedance behavior model, which indicates that TiO2 interfacial modification results in not only increasing the electron extraction but also reducing impedance. This study provides an important and beneficial approach to develop high efficiency PSCs.