Formation and Characterisation of Solution Processed “Pseudo-Bilayer” Organic Solar Cells

Abstract

AbstractThe current state of the art solution processed organic photovoltaic (OPV) cells are based on the bulk heterojunction (BHJ) architecture, consisting of an active layer, in which the donor and the acceptor material are dissolved in a common solvent. In this report, we show that by sequential processing of the active components and by subsequent annealing a “pseudo-bilayer” can be formed which results in an enhanced nanomorphology for efficient charge generation and extraction. The enhanced nanomorphology arises from the inter-diffusion of the PCBM nanoparticles into a layer of pre-organised polymer P3HT instead of a phase separation that happens at the time of spin-coating and annealing in the case of conventional BHJ devices. To get a further insight into the inter-diffusion process, TOF-SIMS depth profiling and XPS measurements were carried out for different thermal annealing treatments of these pseudo-bilayer devices, which show full inter-diffusion after only seconds of annealing at 140°C. The optimised photovoltaic devices that were fabricated showed an efficiency of 4.1%.