Influence of Active Layer and Metal Contact Thickness on P3HT:PCBM Solar Cell Performance

Solar cell efficiency depends on both photogeneration and charge collection, with the active layer playing a key role in these processes. In organic solar cells (OSCs), where power conversion efficiency (PCE) remains relatively low, understanding the influence of active layer and metal contact thickness on device performance is essential. In this work, we investigate the effect of P3HT:PCBM and Ag thickness on OSC performance by analyzing the evolution of electrical parameters obtained from J-V measurements over five weeks, with particular attention given to resistance-related degradation behavior. The analyzed OSCs had a cell structure composed of Ag/P3HT:PCBM/TiO2/ITO/glass, and each material was corroborated by XRD and Raman spectroscopy. The thickness of P3HT:PCBM was modulated by varying the number of spin-coated layers from 1 to 3 (ranging from 75 to 160 nm). This variation increases light absorption, as demonstrated by the optical transmittance spectra. However, device degradation became evident after the third week of fabrication, mainly due to an increase in series resistance, which adversely affected the open-circuit voltage (VOC), fill factor (FF), and overall device efficiency. The best performance was obtained for devices fabricated with two P3HT:PCBM layers and 18 mg of Ag, achieving a maximum PCE of 0.5%.