Morphology and properties of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylenevinylene) (MEH-PPV): N,N′-bis(1-ethylpropyl)-3,4:9,10-perylene bis(tetracarboxyl diimide) (EP-PTC) based solar cells

The influence of two components blend ratio, solution concentration and thermal annealing on the morphology of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylenevinylene) (MEH-PPV): N,N′-bis(1-ethylpropyl)-3,4:9,10-perylene bis(tetracarboxyl diimide) (EP-PTC) blend films spin-cast from chloroform solutions has been studied using atomic force microscopy (AFM). The AFM images show that the dimension of the phase separation increases with the EP-PTC content and total solution concentration. When the annealing temperature increases from 90 to 150 °C, the EP-PTC crystal-like clusters grow rapidly. Solar cells based on MEH-PPV:EP-PTC blend films with different weight ratios were fabricated. The device with 1:3 weight ratio has a higher power conversion efficiency (PCE) of 0.072% compared with the devices with 1:1, 1:2 and 1:4 ratio, which increases by about 14 times over that of the device with 1:1 ratio that has a PCE of 0.005%. It is indicated that the optimum performance of the photovoltaic device is strongly related to the finer phase separation between MEH-PPV and EP-PTC on a submicron scale which enables an efficient dissociation of photogenerated excitons, and the pure EP-PTC phase can build up a percolating network with pathways large enough to enhance electron transport.