Interface modification of organic photovoltaics by combining molybdenum oxide (MoOx) and molecular template layer

We report discrete heterojunction small molecular organic photovoltaics (OPVs) with enhanced performance by modifying the interface using molybdenum oxide (MoOx) and molecular template layer perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride (PTCDA). A large increase in open-circuit voltage was obtained in copper phthalocyanine/fullerene, i.e., CuPc/C-60 and CuPc/PCBM, discrete planar heterojunction photovoltaics with an insertion of 5 nm MoOx hole transport layer at the interface between the anode electrode and the CuPc donor layer. It results from the band bending at the interface and the pinning of the highest occupied molecular orbital level of CuPc to the Fermi level of MoOx due to the defect states (oxygen vacancies) in MoOx thin films. Moreover, the short-circuit current showed an efficient improvement by inserting a 1 nm PTCDA layer at the interface between the MoOx layer and the CuPc layer. The PTCDA layer induces the growth of CuPc thin film with lying-down molecular arrangement, supporting the charge transports along the vertical direction. The power conversion efficiencies of CuPc/C-60 and CuPc/PCBMdiscrete planar heterojunction photovoltaic devices were improved from about 0.80% to 1.50% with inserting both MoOx and PTCDA layers. The results suggest that the performance of organic discrete planar heterojunction photovoltaics could be optimized by interface modification with combining hole transport layer and molecular template layer, which are potentially suitable for other highly efficient OPVs, such as small molecular tandem OPVs. (C) 2014 Elsevier B. V. All rights reserved.