Luminescent down-shifting film based on optimized mixture of organic dyes for improving the performance of P3HT:PC61BM photovoltaic devices

Abstract

During the last few years, great interest has been given to research in organic solar cells. Apart from the low cost techniques needed for the production of the active layers, the plasticity of these types of materials offers an additional benefit compared to traditional silicon-based solar cells. However, the commercialization of organic photovoltaic technologies is limited by rapid degradation and low efficiency. Recently, the use of luminescent down-shifting (LDS) films has been explored as a tool for increasing the external quantum efficiency of organic-based devices. A previously observed superposition in the emission–absorption spectra of Kremer blue (Kb) and Coumarin 7 (C7) dyes suggests that an energy transfer process can take place among these molecules. Decay time photoluminescence measurements in Kb100−xC7x samples were carried out to confirm a Föster resonance energy transfer process. An optimization process following the design of experiments methodology was carried out to adjust the optical properties of Kb100−xC7x films for applications in the P3HT:PC61BM organic photovoltaic device. An increment of 18.6% in the short circuit current density (Jsc) of P3HT:PC61BM devices coated with a Kb92.5C77.5 LDS film was observed. A degradation test shows a rapid drop in the electric current density of devices without the LDS film, which we attribute to the so-called burn-in, widely reported in the literature. For devices coated with the Kb92.5C77.5 LDS film, no rapid drop in the electric current density was observed, suggesting that the use of the luminescent layer mitigates the photoinduced burn-in loss.