Role of exciton blocking layers in improving efficiency of copper phthalocyanine based organic solar cells

Abstract Organic devices based on small molecules such as copper phthalocyanine (CuPc) and Buckminster fullerene (C60) heterostructure design are one of the more promising next generation organic solar cells. We investigated the role of exciton blocking layer (EBL) towards obtaining optimized efficiency of CuPc–C60 based solar cells. Diodes with ITO/HTL/CuPc/CuPc:C60(optional)/C 60 /(EBL)/Al structure were achieved, the active layer being either a heterojunction bilayer, co evaporated layer or a combination. All small molecular films were deposited in an ultra high vacuum system and devices were immediately sealed in a glove box. Current–voltage characteristics and spectral response of the cells were measured. The thickness of the active layers was kept at optimum level given in literature. In case of EBL we focused on the vacuum evaporated small molecule thin films such as bathocuproine (BCP), bathophenanthroline (BPhen) and 1,3,5-tris( N -phenylbenzimidazol-2-yl)benzene (TPBi). We also compared heterostructure and co deposited films. We find that 1,3,5-tris( N -phenylbenzimidazol-2-yl)benzene (TPBi) works as efficient exciton blocking layer. Further, we obtain lower shunt resistance in co deposited films compared to the heterojunctions.