The improvement of bulk-heterojunction order in polymer photovoltaic device

The blend morphology and vertical arrangement are critical to the performance of organic bulk-heterojunction photovoltaic devices. In the present paper, the authors proposed a new annealing method that controls the blend morphology and vertical arrangement of two materials by means of simultaneously applying external electrical field and violet irradiation on the active layer of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) during annealing process. By using this annealing method, the power conversion efficiency increased by 36%, which was caused by vertical phased-separated blend of crystalline P3HT and PCBM and better charge extraction of electrodes. X-ray photoelectron spectroscopy (XPS) was measured to prove more fullerene derivatives at the organic/cathode interfaces by using this annealing method. The X-ray diffraction (XRD) analysis and UV-Vis absorption spectrum analysis also revealed more ordered polymer crystallization.