The blending of organic semiconductor and insulating polymer as an active layer of organic transistors has been assessed by several studies and may open new possibilities for advantageous functions. However, studies on the use of insulating polymer doping in organic solar cells are rarely conducted. In this research, a blending film comprising regioregular poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was doped with a soft insulating poly(methyl methacrylate) (PMMA) to act as an active layer of a solar cell. The fill factor (FF) and open-circuit voltage (VOC) of P3HT:PCBM solar cells were improved after PMMA doping. The microstructure- dependent photovoltaic properties of devices with different fractions of PMMA were investigated using spectroscopy and quantum chemical calculations. We highlight that PMMA doping leads to a more homogeneous conformation of P3HT chains, fewer vacancies, and fewer leakage pathways in blending films. Consequently, charges can be efficiently transported to the electrodes of devices, resulting in enhanced FF and VOC. The results of theoretical calculations at the microscopic molecular level also confirmed the enhanced electrical performance of devices from PMMA doping.
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