Balance Between Light Absorption and Recombination Losses in Solution-Processed Small Molecule Solar Cells with Normal or Inverted Structures

摘要

Comparison of the photovoltaic properties of F3:fullerene bulk heterojunction solar cells (where F3 is a donor molecule of intermediate dimensions) with normal and inverted structures as a function of photoactive layer thickness is carried out by using optical modeling and light-dependent photoelectrical characterization. The larger short circuit current of inverted devices can be explained by higher light absorption in the active layer, relative to normal devices. However, worse charge extraction conditions and trap-assisted recombination, in the bulk heterojunction blend in inverted devices, give rise to larger nongeminate recombination losses and an opposite thickness dependence of the short circuit current and fill factor than what is observed in counterparts with the conventional device architecture.