We fabricated bulk heterojunction organic solar cells based on 1,2-dichlorobenzene solutions of poly[[4,8-bis[(2-ethylhexyl) oxy]benzo[1,2-b:4,5-b'] dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl) carbonyl]thieno [3,4-b]-thiophenediyl]] (PTB7): [6,6]-phenyl-C71-butyric-acid-methyl-ester (PTB7:PC71BM) with additional dimethyl sulfoxide (DMSO) and surfactants diiodooctane (DIO). The optimal weight ratios of DMSO and DIO relative to the total weight of PTB7:PC71BM were 13% and 3%, respectively, and the resulting solar cells exhibited an open circuit voltage of 0.72 V, short circuit current density of 15.63 mA/cm2, fill factor of 0.49, and power conversion efficiency of 5.47%. The surfaces of the active layers deposited with added DMSO and DIO were smoother than those of the layers without the added surfactants and consisted of smaller nanograins, which may have resulted in the improved solar cell performance.

We characterized bulk-heterojunction (BHJ) solar cells using a new phenylene-thiophene oligomer, 3,7-bis[5-(4-n-hexylphenyl)-2-thienyl]dibenzothiophene-5,5-dioxide (37HPTDBTSO), and phenyl-C61-butyric-acid methyl ester (PCBM). Their photovoltaic properties including current-voltage characteristics and spectrum response were investigated. It was found that 37HPTDBTSO is appraised to be valuable electron donor. The characteristics of BHJ solar cells using mixed two donors of 37HPTDBTSO and a polymer of poly(3-hexylthiophene) (P3HT) were further investigated. OSC using the blend film of mixed donars and PCBM achieved a power conversion efficiency of 0.89%.