Fabrication of bulk heterojunction photovoltaic devices using sublimable rhenium diimine complexes as photosensitizers

Abstract

A series of chlorotricarbonyl rhenium (I) bis(phenylimino)acenaphthene (Re-DIAN-X) complexes were used as the photosensitizers for photovoltaic cells. Unlike other transition-metal-based photovoltaic sensitizers that can only be prepared by solution method, these complexes are sublimable. Compared to other rhenium diimine complexes based on bipyridine or 1,4-diaza-1,3-butadiene ligands, these complexes have lower band gaps, which can be modified easily by changing the structure of the ligand. It allows the preparation of blend of metal complexes in order to broaden the sensitization region in UV-vis absorption spectrum. One of the complexes also shows bipolar charge transport character with relatively high charge carrier mobilities in the order of 10 -3 cm2V-1s-1. Multilayer heterojunction and bulk heterojunction devices with fullerene as the electron accepting molecule were prepared. For the bulk heterojunction devices, the fill factor and power conversion efficiency under AM 1.5 simulated solar light illumination were 0.51 and 1.29 %, respectively. The effects of changing the Re-DIAN/C60 film thickness, Re-DIAN/C60 ratio and variation of ligand structures in the bulk heterojunction devices were studied. The amount of photosensitizer and electron transport molecules may strongly affect the balance between the photon absorption, exciton formation, dissociation, and charge transport processes. Atomic force microscopic images showed that the complex dispersed evenly with fullerene molecules in solid state.