Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV23)
Publication date: 30th March 2023
Charge generation can proceed through two different paths in bulk heterojunction (BHJ) based organic solar cells (OSC) which are electron transfer from donor to acceptor and hole transfer from acceptor to donor. These processes can be controlled by electron affinity (EA) offsets and ionization energy (IE) offsets, respectively. Understanding the relationship between the IE offsets, EA offsets between donor and acceptor materials, and the performance of OSCs could improve the charge generation efficiency. We characterized the impact of large IE and EA offsets on device performances and more precisely on the internal quantum efficiency (IQE) using a wide bandgap polymer donor which has shallow IE: poly(3-hexylthiophene-2,5-diyl)(P3HT) and non-fullerene acceptors (NFA). This provides a wide range of diagonal bandgaps (energy difference between the IE of the donor and the EA of the acceptor). We found that IQE decreases when the diagonal bandgap decreases. Thus, enables us to understand the relation between small diagonal bandgap and the decrease of the IQE in energy gap law framework. However, we observed low IQE, we also observed high exciton quenching which indicates efficient charge transfer in these systems. The low IQE can be explained due to charge recombination as our results demonstrated by geminate and non-geminate recombination. Understanding the relation between these different energy offsets and device performance would improve the power conversion efficiency (PCE), thus, pave the way towards more reliance on renewable energy.