Increased efficiency in small molecule organic photovoltaic cells through electrode modification with self-assembled monolayers

We report that through the incorporation of polar self-assembled monolayers (SAMs) at the indium tin oxide (ITO)/donor interface in chloroaluminium phthalocyanine (ClAlPc)/C(60) discrete heterojunction organic photovoltaic (OPV) cells, the power conversion efficiency can be dramatically increased. This enhanced performance is due to better alignment between the hole-extracting electrode Fermi level and the highest occupied molecular orbital (HOMO) of the ClAlPc donor, as well as an improved surface compatibility which provides a more optimised electrode/donor interface. Optimised cells demonstrate an increase of similar to 85% in open circuit voltage which results in a near three-fold increase in power conversion efficiency from 1.3% to 3.3% under 1 sun illumination. Comparative studies are made using cells based on two other organic donor materials, copper phthalocyanine (CuPc) and boron sub-phthalocyanine (SubPc).