| In this thesis,we studied the influences of solvent-related processing techniques on the performance and active layer morphology of polymer solar cells(PSCs).By applying solvents with different acceptor solubilities,including acetone,toluene,chloroform(CF)and o-dichlorobenzene(o-DCB),the effects of solvent vapor annealing(SVA)on the performance of PSCs were systematically investigated.After analyzing the variation of PSC performance and the morphology of active layer,we find that acceptor solubility of SVA solvent plays an important role in controlling the morphology of active layer blend.Especially,the PSC treated by o-DCB with the highest acceptor solubility exhibits a remarkable enhancement of power conversion efficiency(PCE)from 6.13%(as cast device)to 7.61%.The performance improvements are mainly due to the formation of the improved phase separation of active layer blend,resulting in efficient charge separation,balanced charge transport and suppressed charge recombination.The effects of different binary-solvent treatments on the performance of PSCs were also systematically investigated.The binary-solvent was obtained by mixing a primary solvent of methanol(MeOH)with a secondary solvent comprising of 2-chlorophenol(2-CP),dimethylsulfoxide(DMSO),or o-xylene(o-XY).After analyzing the variation of photovoltaic performance and the nanostructure morphology of active layers,we find that the relative polarity of the secondary solvent exhibits significant impact on the nanostructure morphology of active layer blends.Especially,2-CP with the highest relative polarity mixed with MeOH can significantly increase the PCE from 6.47%(MeOH treated device)to 7.81%.The improved photovoltaic performances of binary-solvent treated PSCs are mainly due to the enhanced light absorption,optimized blend morphology,and increased charge carrier mobilities,resulting in efficient exciton generation,effective charge separation,and balanced charge transport. |
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