Spectroscopic study of P3HT:PCBM deposited by electrospray deposition

Abstract

We investigated a molecular order of poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61-butyric acid methyl ester thin film by judging from the Raman spectrum, and a crystallinity parameter was estimated as the molecular order of poly(3-hexylthiophene-2,5-diyl). The crystallinity parameter of spin-coated sample increased with increasing annealing temperature, and this result relates to the photoconversion efficiency of photovoltaic cell. This means that the high photoconversion efficiency can be obtained due to the high crystallinity parameter of poly(3-hexylthiophene-2,5-diyl), and this result is reasonable compared to the previous researches. In addition, the crystallinity parameter of electrosprayed thin film increased with increasing applied voltage, corresponding to the supply speed of solution. Since the droplet size increased with increasing supply speed, the evaporation speed of solvent (o-dichlorobenzene) became slow at the high applied voltage. Therefore, the slow evaporation speed of solvent caused the molecular order in the active layer. As a result, the maximum of approximately of 95 % was achieved even though the sample was not thermally annealed, and this value corresponds to the thermal annealing at 100 °C.