Interface-engineering additives for inverted BHJ polymer solar cells

We report on the photovoltaic (PV) effect of inverted polymer solar cells (PSCs) with a bulk-heterojunction (BHJ) PV layer consisting of a donor-conjugated polymer of poly(3-hexylthiophene) (P3HT) and an acceptor of [6,6]-phenyl C-61 butyric acid methyl ester (PCBM) mixed with an interface-engineering additive of poly(oxyethylene tridecyl ether) (PTE). The electron-selective layer used is sol-gel processed zinc oxide (ZnO), and the anode layer is silver (Ag). Improved performance was achieved using the PTE additive in the BHJ PV layer of the inverted PSCs. A 1.77 wt% mixing level of PTE into a blended P3HT:PCBM PV layer with a ratio of 1.00:0.73 produces a power conversion efficiency (PCE) of 3.14%, which was much higher than the reference device (2.77%) without PTE. This improvement can be attributed to not only the improved carrier transport due to the PTEs at the interfaces between the BHJ PV layer and the electrodes, but also the increased carrier lifetime due to the PTE molecules at the interfaces between the phase-separated BHJ domains. These results suggest that the BHJ PV layer mixed with the PTE interface-engineering additive is a promising functional composite material system for use in efficient inverted polymer PV cells. (C) 2012 Elsevier B.V. All rights reserved.