Efficient and low cost inverted hybrid bulk heterojunction solar cells

In this study, hybrid bulk heterojunction solar cells with an inverted architecture were fabricated using solution processing techniques. ZnO and TiO₂ nanoparticles were then incorporated to the active layer which primarily consists of poly (3-hexylthiophene) (P3HT) and [6,6] phenyl-C61-butyric acid methyl ester (PCBM). The devices were prepared with varying ratios of PCBM to nanostructured inorganic oxides (ZnO and TiO₂) while keeping a fixed amount of P3HT. Various characterization techniques were used to understand the effect of metal oxide nanoparticles on structure, morphology, and performance of resulting devices. It was observed that incorporating an optimum amount of nanoparticles to the active layer increased charge carrier mobility, surface roughness of the active layer, and absorption in visible region leading to a significant increase in power conversion efficiency. However, a significant agglomeration of nanoparticles was observed as their ratio relative to PCBM increased and they completely agglomerated in the absence of the fullerene derivative.