Excitation Wavelength Dependent Internal Quantum Efficiencies in a P3HT / Non-Fullerene Acceptor Solar Cell

Solar cells based on blends of the donor polymer, P3HT, with the non-fullerene acceptor, IDTBR, have been shown to exhibit promising efficiencies and stabilities for low cost organic photovoltaic (OPV) devices. We focus herein on the charge separation and recombination dynamics in such devices. By employing selective wavelength excitations of P3HT and O-IDTBR, we show that photoexcitation of the P3HT results in lower internal quantum efficiency (IQE) for photocurrent generation than observed for photoexcitation of the O-IDTBR. Transient absorption and photoluminescence quenching studies indicate that this lower IQE results primarily from higher geminate recombination losses of photogenerated charges following P3HT excitation compared with O-IDTBR excitation, rather than from differences in exciton separation efficiency. These higher geminate recombination losses result not only in a lower photocurrent generation efficiency at short circuit, but also a lower device J-V fill factor upon selective excitation of the P3HT donor, when compared with O-IDTBR excitation.