Employing TiO2 nanorods to improve inverted polymer solar cells

In this study, our investigations adapt several approaches to improve the device characteristics of PSCs with inverted structures. First, we employ PV2000 as a photoactive layer, which has a large relative energy difference between the HOMO level of the electron-donating polymer and the LUMO level of the electron acceptor (energy difference ~1.7 eV), so leading to a large VOC. Second, solution-processed TiO₂ nanorods are inserted between the sol-gel derived ZnO layer and photoactive layer to improve the efficiency of inverted devices. The charges in the photoactive layer are collected and transported via the nanorods with relatively higher carrier mobility, so leading to improve the series resistance. Moreover, the photoactive layer is thickened due to the introduction of TiO₂ nanorods, indicating improved light harvest and photocurrent. Here, we report that inverted PSCs have high power conversion efficiency of 5.61% with Jsc=11.31 mA cm^-2, Voc=0.78V, and FF=63.5% under AM 1.5G (100mW/cm²) irradiation intensity.