Signi cant Enhancement in Built-in Potential and Charge Carrier Collection of Organic Solar Cells using 4-(5-hexylthiophene-2-yl)-2,6-bis(5-tri uoromethyl)thiophen-2-yl)pyridine as a Cathode Bu er Layer

An electron transporting material of TFTTP (4-(5-hexylthiophene-2-yl)-2,6-bis(5-trifluoromethyl)thiophen-2-yl)pyridine) was investigated as a cathode buffer layer to enhance the power efficiency of organic solar cells (OSCs) based on subphthalocyanine and C₆₀. The overall power conversion efficiency was increased by a factor of 1.31 by inserting the TFTTP interfacial layer between the active layer and metallic cathode. The inner mechanism responsible for the performance enhancement of OSCs was systematically studied with the simulation of dark diode behavior and optical field distribution inside the devices as well as the characterization of device photocurrent. The results showed that the TFTTP layer could significantly increase the built-in potential in the devices, leading to the enhanced dissociation of charge transfer excitons. In addition, by using TFTTP as the buffer layer, a better Ohmic contact at C₆₀/metal interface was formed, facilitating more efficient free charge carrier collection.