Improvement of heterojunction donor/acceptor organic photovoltaic devices by employing additional active layer

Single-heterojunction (HJ) donor/acceptor photovoltaic devices composed of copper phtalocyanine (CuPc) and 3,4,9,10-perylenetetracarboxylic bis-benzimidazole (PTCBI) sandwiched between indium-tin-oxide (ITO) and Ag top electrode were investigated. An improvement in device performance was obtained by inserting another perylene derivative, 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) between the CuPc and the PTCBI layers. In this case, the PTCDI and the PTCBI act as an active layer and a buffer, respectively. The active layer increased the absorption efficiency of incident photons, while the buffer provided an ohmic contact with the Ag top electrode. The power conversion efficiency (PCE) was improved from 0.81% for the reference device (without a PTCDI layer) to 1.13% for the optimized single-HJ device (with a PTCDI layer). The concept found in the single-HJ device was introduced into the stacked tandem triple-HJ devices. The improvement of power conversion efficiency, however, was achieved by inserting the PTCDI layer between the PTCBI and the top electrode.