||Emission from Charge-Transfer States in Bulk Heterojunction Organic Photovoltaic Cells Based on Ethylenedioxythiophene-Fluorene Polymers
Yasuda, Takeshi ,
Kuwabara, Junpei ,
Han, LiyuanKanbara, Takaki
Molecular Crystals and Liquid Crystals
111 , 2015-12 , Taylor and Francis, Inc
We investigated the electroluminescence (EL) from charge-transfer (CT) in the interface state of PEDOTF/PC70BM, known to be empirically related to Voc, to elucidate a difference in Voc of 0.24 V in bulk heterojunction (BHJ) organic photovoltaic cells (OPVs) based on two polymers (H-PEDOTF and S-PEDOTF with a high and low molecular weight, respectively) having almost the same HOMO energy levels. The difference in the energies of CT EL peaks is relatively small (0.06 eV) compared to the difference in the Vocs. Consequently, we mainly attribute the excessive loss of Voc in S-PEDOTF-based OPVs to a trap assisted recombination mechanism.