Stoichiometric dependence of TiOx as a cathode modifier on band alignment of polymer solar cells

Abstract In this study, we systematically investigated the stoichiometric dependence of titanium oxide (TiO x , x =1.56–1.93) as a cathode modifier on the device performance of polymer solar cells. Electronic structures of the synthesized TiO x modifier layers were controlled by tuning the compositions of various O/Ti ratios. The effective cathode work-functions and the corresponding device performances of polymer solar cells are systematically changed as a result of inserting the TiO x modification layers. Interfacial modification of the Al cathode with a low O/Ti ratio of TiO x layer yields the best performing photovoltaic device as a result of a largest built-in potential. The correlation of power conversion efficiencies and carrier dynamics of these devices by inserting various TiO x modification layer is further examined by using the Mott-Schottky analysis and the impedance spectroscopy technique. The consistent result shows an enhanced carrier collection efficiency and a reduced charge recombination rate of the device via adequate band alignment between the photoactive layer and the cathode using the TiO x modification layer with an optimized O/Ti ratio.