Fig. 2. (a) The J–V curves (left) and the external quantum efficiency spectra (right) of the optimized devices based on P4:PC₇₁BM blend films (weight ratio = 1 : 3). Reproduced from ref. 29 with permission from the American Chemical Society, copyright 2010. (b) The AFM phase images of P4:PC₇₁BM blend films (weight ratio = 1 : 3). Reproduced from ref. 29 with permission from the American Chemical Society, copyright 2010. (c) XRD data (left) and the illustration of lamellar structure (right) of P7 film. Reproduced from ref. 31 with permission from the Royal Society of Chemistry, copyright 2015. (d) The OSC performances of P8:PC₇₁BM with different ratios. Reproduced from ref. 32 with permission from the Royal Society of Chemistry, copyright 2017.