Energy Level Tuning of Non-fullerene Acceptors in Organic Solar Cells

This document is the unedited author's version of a Submitted Work that was subsequently accepted for publication in Journal of the American Chemical Society , copyright © American Chemical Society after peer review. To access the final edited and published work, see http://pubs.acs.org/doi/abs/10.1021/jacs.5b02808The use of non-fullerene acceptors in organic photovoltaic devices could lead to enhanced efficiencies due to increased open-circuit voltages (VOC) and improved absorption of solar light. Here we systematically investigate planar heterojunction devices comprising peripherally substituted subphthalocyanines as acceptor, and correlate device performance with heterojunction energetics. Due to a balance between VOC and photocurrent, tuning of the interface energy gap is necessary to optimize power conversion efficiency in these devices. In addition, we explore the role of the charge transport layers in the device architecture. It is found that non-fullerene acceptors require adjusted buffer layers with aligned electron transport levels to enable efficient charge extraction, while the insertion of an exciton blocking layer at the anode interface further boosts photocurrent generation. These adjustments result in a planar heterojunction OPV device with 6.9% efficiency and a VOC above 1 V.The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement 287818 of the X10D project and from the European Community’s ERC Advanced Grant # 320680 (EPOS CRYSTALLI). This work is also supported by the Spanish MINECO (CTQ-2014-52869-P) and Comunidad de Madrid (S2013/MIT-2841, FOTOCARBON