Exciton-blocking phosphonic acid-treated anode buffer layers for organic photovoltaics

We demonstrate significant improvements in power conversion efficiency of bilayer organic photovoltaics by replacing the exciton-quenching MoO3 anode buffer layer with an exciton-blocking benzylphosphonic acid (BPA)-treated MoO3 or NiO layer. We show that the phosphonic acid treatment creates buffers that block up to 70% of excitons without sacrificing the hole extraction efficiency. Compared to untreated MoO3 anode buffers, BPA-treated NiO buffers exhibit a similar to 25% increase in the near-infrared spectral response in diphenylanilo functionalized squaraine (DPSQ)/C-60-based bilayer devices, increasing the power conversion efficiency under 1 sun AM1.5G simulated solar illumination from 4.8 +/- 0.2% to 5.4 +/- 0.3%. The efficiency can be further increased to 5.9 +/- 0.3% by incorporating a highly conductive exciton blocking bathophenanthroline (BPhen):C-60 cathode buffer. We find similar increases in efficiency in two other small-molecule photovoltaic systems, indicating the generality of the phosphonic acid-treated buffer approach to enhance exciton blocking. (C) 2013 AIP Publishing LLC.