Effects of Annealing Temperature on the Performance of Organic Solar Cells Based on Polymer: Non-Fullerene Using V2O5 as HTL

The annealing temperature and thickness are two important factors to optimize the morphology of the active layer for a better performance of inverted polymer solar cells (iPSCs). Herein, the effects of the annealing temperature and the thickness of the active layer on the performances of iPSCs based on PBDB-T:IT-M are analyzed. Titanium oxide and vanadium oxide are used as electron and hole transporting layers, respectively. The device made with PBDB-T:IT-M layer (ca. 90 nm thick) thermally annealed at 100 °C exhibits the best performing under simulated AM 1.5G light. The idealities factor of iPSCs with two different annealing temperatures are determined by measuring the open-circuit voltage as a function of light intensity. The study shows that recombination losses in iPSCs annealed at 160 °C are governed by non-geminate recombination mechanisms, while in iPSCs annealed at 100 °C, the recombination losses are mainly due to band-tail trap states. Additional impedance spectroscopy measurements reveal that the device with an annealing temperature of 160 °C exhibits a higher charge-transfer in the bulk layer. However, the device thermally annealed at 100 °C shows lower charge-transfer resistance through all layers involved in the charge extraction. The results of this work show the importance of the annealing temperature on the charge-transfer at the active layer/vanadium oxide interface.