Charge generation and transport in efficient organic bulk heterojunction solar cells with a perylene acceptorElectronic supplementary information (ESI) available: Device fabrication procedure, excitation density dependent μs-TAS, blend composition dependent μs-TAS, power law decay fit of different acceptor blends, fs-TA spectra at different excitation wavelengths and intensities, SCLC measurements on e-only and h-only devices. See DOI: 10.1039/c3ee42484g

The origin of high current density in efficient non-fullerene based bulk heterojunction (BHJ) organic solar cells employing a non-planar perylene dimer (TP) as an electron acceptor and a thiophene based donor polymer PBDTTT-CT is investigated using electrical and optical techniques. Photoluminescence measurements reveal almost complete quenching of both the donor and acceptor excitons, indicating efficient electron and hole transfer processes. The nanomorphology of the films shows fine mixing of the donor polymer and TP at 50 : 50% weight ratio with a photon to current conversion efficiency (IPCE) of 45% in the visible regime. At the donor-acceptor interface, both polymer and TP excitons undergo fast dissociation with similar time scales of a few picoseconds. The magnitude of the polaron yield of PBDTTT-CT:TP blends is observed to be comparable to that of PBDTTT-CT:PC 70 BM blends and exhibits similar μs-decay dynamics. A power conversion efficiency of 3.2% is achieved for devices with 50 : 50% by weight compositional ratio of polymer and TP. Efficient photoinduced electron and hole transfer between PBDTTT-CT and TP, covering the entire visible range for efficient non-fullerene BHJ solar cells.