Imbalanced charge mobility in oxygen treated polythiophene/fullerene based bulk heterojunction solar cells

The effect of oxygen induced traps on charge mobility in bulk heterojunction solar cells using poly(3-hexylthiophene) (P3HT):l-(3-methoxycarbonyl)-propyl-l-phenyl-(6, 6) methanofullerene (PCBM) blend have been studied using photoinduced charge extraction by linearly increasing voltage (PhotoCELIV) technique. The solar cells exposed to oxygen exhibit dual PhotoCELIV peaks, whereas the solar cell without oxygen treatment show single PhotoCELIV peak with the charge mobility of the order of 10−4 cm2/V s. It is demonstrated that the oxygen treatment imbalance the charge mobility in the P3HT/PCBM photoactive layer, which affects the power conversion efficiency and lifetime of the solar cell. The single PhotoCELIV peak for the device without oxygen treatment indicates that the charge mobility is balanced, that causes the overlapping of electron and hole transients.