The role of acceptor-rich domain in optoelectronic properties of photovoltaic diodes based on polymer blends

We investigate how the acceptor-rich domain influences the microstructure and photoluminescence properties, and consequently the external quantum efficiency of photovoltaic diodes based on blend films of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(N,N′-diphenyl)-N,N′di(p-butyl-oxy-pheyl)-1,4-diaminobenzene)] (PFB) and poly[9,9-dioctylfluorenyl-2,7-diyl)-co-1,4-benzo-{2,1′–3}-thiadiazole)] (F8BT). We find that the interfacial area depends strongly on the size and density of acceptor- or F8BT-rich domains in the phase-separation scheme. There exists an optimized density and size distribution of the F8BT-rich domains, which favors spatial charge dissociation. Meanwhile, the balance of charge percolation between the donor(PFB)- and acceptor(F8BT)-rich domains also plays important roles in charge extraction and collection.