Fig. 1
From: Probing the pathways of free charge generation in organic bulk heterojunction solar cells
Scheme of the TDCF method, energy level diagram and device performances: a Scheme of the elementary excitations and processes involved in absorbed photon-to-electron formation. Geminate and non-geminate recombination occur at different time scales at AM1.5G-relevant carrier densities. Therefore, applying a strong reverse bias in TDCF prior to the onset of non-geminate recombination allows free charge formation due to the separation of CT states to be measured. b Energy level diagram for the materials used in this study. Arrows indicate the pathways of charge formation via electron (channel 1) or hole transfer (channel 2) across the donor-acceptor heterojunction. The energy offset at the heterojunction is reduced by substituting PCBM with ICBA or PCPDTBT with 1F-PCPDTBT. c Current voltage characteristics of the studied blends with a thickness of approx. 110 nm under simulated AM1.5 G illumination. As expected, increasing the energy of the charge separated state (by either lowering the polymer HOMO and/or heightening the acceptor LUMO) increases the Voc, but there is no trivial connection between the energetics of the blend and the overall device performance
