Efficient and stable inverted polymer solar cells using TiO2 nanoparticles and analysized by Mott-Schottky capacitance

The performance of both inverted and conventional polymer solar cells (PSCs) were examined with a low-temperature, solution-processed synthesized TiO2 nanoparticles (TiO2 NPs) as the electron extraction layer. The performance of inverted PSCs based on P3HT:PCBM bulk-heterojunction with a TiO2 NPs layer was dramatically improved and the highest power conversion efficiency (PCE) of 4.56% was achieved via 24 h exposure in air, which is one of the highest PCEs for P3HT:PCBM bulk-heterojunction PSCs using TiO2 as electron extraction layer. Meanwhile, the performance of inverted PSCs was superior to regular PSCs. Mott-Schottky capacitance analysis was carried out for both inverted and regular PSCs to obtain the built-in potential, the depletion width, as well as the doping level of the active layer, which all support the performance improvement of PSCs devices with inverted structure. In addition, inverted PSCs show excellent stability in air without encapsulation. The PCE can retain 87% of its original values after 400 h exposure in air, which is much better than that of regular PSCs. The results indicate that solution-processed TiO2 NPs shows great potential applications in the fabrication of highly efficient and stable inverted PSCs as well as large-area, flexible printed PSCs. (C) 2014 Elsevier B. V. All rights reserved.