High Efficiency Inverted Organic Solar Cells with a Neutral Fulleropyrrolidine Electron-Collecting Interlayer

A novel fulleropyrrolidine derivative, named FPNOH, was designed, synthesized, and utilized as an efficient electron-collecting (EC) layer for inverted organic solar cells (i-OSCs). The grafted diethanolamino-polar moieties can not only trigger its function as an EC interlayer, but also induce orthogonal solubility that guarantees subsequent multilayer processing without interfacial mixing. A higher power conversion efficiency (PCE) value of 8.34% was achieved for i-OSC devices with ITO/FPNOH EC electrode, compared to that of the sol-gel ZnO based reference devices with an optimized PCE value of 7.92%. High efficiency exceeding 7.7% was still achieved even for the devices with a relatively thick FPNOH film (16.9 nm). It is worthwhile to mention that this kind of material exhibits less thickness dependent performance, in contrast to widely utilized p-type conjugated polyelectrolytes (CPEs) as well as the nonconjugated polyelectrolytes (NCPEs). Further investigation on illuminating intensity dependent parameters revealed the role of FPNOH in reducing interfacial trap-induced recombination at the ITO/active layer interface.