Resumo

In this work it is explored the use of two mixed organic dyes, Kremer Blue (Kb) and Coumarin 7 (C7), to design optical filters for applications in the P 3HT : P C 61 BM Or- ganic Photovoltaic device. The use of the filter was intended to increase the External Quantum Efficiency of the device by means of the Luminescent Down-Shifting (LDS) effect, at the same time that is expected to be used for preventing fast UV degradation of the solar cell. It was found that the sample Kb 92.5 C7 7.5 dissolved in a PMMA solu- tion (3 mg/mL) has a PLQY of 93.6%, the highest value obtained in the optimization process. Figures of merit of this material, accompanied by simulations of the EQE us- ing the Rothemund model reveal that this sample would contribute to an increment of 19.8% in the photo-generated current of the device. The I-V characteristic curve was measured for eight devices and the average change in current density obtained was 18.6%. Time-resolved PL results show a decrease in the lifetime of samples with different con- centrations of C7, compared to the lifetime of single Kb samples. This result suggest that exist an energy transfer process, presumably mediated by a Föster mechanism. The photo-generated current was measured upon solar exposure, with and without the LDS filter, for non encapsulated devices. It was found that during the first 3 hours of solar exposure, the samples with the LDS filter present higher photo-generated current values when compared to devices without the filter. However, upon longer exposure, a rapid drop in the generated current for both devices (with and without filter) was observed. Although increments in the photo-generated current were achieved by means of the LDS filter, further improvements are needed in order to enhance the lifetime of the device.