Contrary interfacial exciton dissociation at metal/organic interface in regular and reverse configuration organic solar cells

An opposite interfacial exciton dissociation behavior at the metal (Al)/organic cathode interface in regular and inverted organic solar cells (OSCs) was analyzed using transient photocurrent measurements. It is found that Al/organic contact in regular OSCs, made with the blend layer 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):3′H-Cyclopropa [8,25][5,6] fullerene-C70-D5h(6)-3′-butanoicacid,3′-phenyl-,methyl ester (PC₇₀BM), always hampers the electron collection. However, this is not observed in their reverse geometry OSCs fabricated using the same PTB7:PC₇₀BM blend system. The detrimental interfacial exciton dissociation in regular OSCs originates the compensation of field drifted photo-generated electrons at Al/organic interface. The unfavorable interfacial exciton dissociation can be eliminated, e.g., by interposing a ZnO-based interlayer between Al and organic layer, attaining an efficient electron collection, thereby power conversion efficiency.