Solution processed hybrid Graphene-MoO3 hole transport layers for improved performance of organic solar cells

A facile hydrothermal process is used to prepare hybrid graphene-MoO3 particles to be used as hole transport layers (HTLs) in organic solar cells (OSCs). The OSCs with active layer donor/acceptor combinations of Poly[N-9 ''-hepta-decanyl-2,7-carbazolealt 5,5 (4',7'-di-2 thieny1-2',1',3'-benzothiadiazole)] (PCDTBT) and fullerene derivative [6,6]-phenyl-C71-butyric acid methylester (PC71BM) exhibit an enhanced power conversion efficiency (PCE) of 7.07%, an increase by 19% with the hybrid HTL compared to those devices with only MoO3 HTLs. Through investigating the optical and electrical properties of the devices, we found that the superior PCE originates from an enhanced hole transport property resulting from the extraction capabilities of G-MoO3. Comparing with thermal evaporated MoO3, the G-MoO3 exhibits a higher optical transmittance, improved electrical conductivity and enhanced hole mobility. Moreover, the work function of the hybrid G-MoO3 was close to the highest occupied molecular orbital (HOMO) level of PCDTBT, which reduced the energy barrier for the carriers and was suited for hole transport.