Water-based organic solar cells from Janus nanoparticles: Closing the performance gap with reference cells

Abstract

P3HT:PC61BM Janus nanoparticles prepared through nanoprecipitation were integrated in inverted solar cells with three different surfactants: an anionic (SDS), a cationic (C16TAB) and a neutral (pluronic F127). An investigation of the properties at the dispersed state showed no difference between all the surfactants. A thermogravimetric titration method was developed to calculate the residual amount of surfactant in the dispersions. The higher residual content of surfactant in the dispersions resulted in lower electronical properties. The optimum balance was found with SDS, showing the lower surfactant quantity required to achieve nanoparticle stabilisation (10%W), resulting in the minimum amount of insulating molecule in the active layer (PCE = 1.7 %).A systematic comparison is made, between a reference system, solar cells made from a o-dichlorobenzene solution of the active materials (power conversion efficiency (PCE) = 3.2 %). Atomic force microscopy revealed that best performances were linked to the complete sintering of the nanoparticles and an optimisation of the film morphology. While PC61BM aggregation was identified for SDS-based solar cells, a less pronounced aggregation was observed for pluronic F127. To solve this issue, we demonstrated that a slight addition of Pluronic F127 (4%w) in SDS-stabilised dispersion prior to processing the active layer not only ensured a better film formation, but avoided the PC61BM aggregation. As a result, a significant improvement of efficiencies was achieved (PCE = 2.44 %) approaching the reference solar cell efficiency.