The effect of uni- and binary solvent additives in PTB7:PC61BM based solar cells

•The power conversion efficiency of thin film organic solar cell improved by 120% using binary solvent additives in ambient device preparation condition.•The charge mobility is enhanced by one order of magnitude using co-solvents compared to single additives.•The formation favorable donor/acceptor phase segregations was responsible for device performance improvement.•Better device stability was achieved by the use of co-solvents additives. The effect of uni- and binary solvent additives on the performance of organic solar cells based on poly4,6-(2-ethylhexyl-3-fluorothieno [3,4-b]thiophene-2-carboxylate)alt-2,6(4,8-bis(2-ethylhexyloxy) benzo [1,2-b:4,5-b]dithiophene) (PTB7) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was investigated using chloroform host solvent. The use of binary solvents additive was found to be more effective in improving the collection of photo-generated current in thin film organic solar cells (TFOSC). The difference in the boiling points of the solvents and their ability to dissolve fullerene molecules from the blend are some of the critical factors that determines the effect of binary solvents additive. The inclusion of solvent additives in device processing improved the power conversion efficiency of TFOSC which can be attributed to the polymer crystallinity and the formation of favourable phase separated domains for the percolation of free charge carriers. Moreover, the investigations on the charge transport properties suggest that a little reduction in the non-germinate recombination was realized leading to the improved charge extraction in the devices with binary solvents additive compared to those processed without additive solvent.