Current Photovoltaic Research ISSN:2288-3274(Print) 2508-125X(Online)

Here we report the influence of thermal treatment on the performance of high efficiency polymer solar cells with the bulk heterojunction films of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b'] dithiophene-alt-3-fluorothieno[3,4-b]thiophene-2- carboxylate] (PTB7-Th) and [6,6]-phenyl C71 butyric acid methyl ester (PC₇₁BM). The crystalline nanostructure of PTB7-Th:PC₇₁BM layers, which were annealed at three different temperatures, was investigated by employing synchrotron radiation grazing incidence X-ray diffraction (GIXD) technique. Results showed that the device performance was slightly reduced by thermal annealing at 50°C but became significantly poor by thermal annealing at 100°C. The poor device performance by thermal annealing was attributed to the collapse in the crystalline nanostructure of PTB7-Th in the PTB7-Th:PC71BM layers as evidenced by the GIXD measurements that exhibited huge reduction in the intensity of PTB7-Th (100) peak even at 50°C.