Cascaded Energy and Charge Transfer Synergistically Prompting 18.7% Efficiency of Layered Organic Solar Cells with 1.48 eV Bandgap

Series of layer-by-layer organic solar cells (LOSCs) are constructed by sequentially spin-coating donor layer and acceptor layers. A champion power conversion efficiency (PCE) of 18.79% is achieved from the LOSCs with PBQx-TCl/ITIC/PY-DT as active layers, which should be one of the top values among the OSCs with optical bandgap over 1.48 eV. The middle bandgap material ITIC has a complementary photon harvesting range with PBQx-TCl and PY-DT, leading to the enhanced photon harvesting of active layers. Meanwhile, ITIC can play a vital role in energy and charge transfer relay to increase exciton utilization and charge transport, which can be confirmed from the varied FFs of normal or inverted LOSCs with ITIC/PY-DT or PY-DT/ITIC as acceptor layers. Over 7% PCE improvement of LOSCs can be achieved by employing ITIC as the middle layer to form cascaded energy and charge transfer in the active layers. This work may provide an efficient strategy for improving the performance of LOSCs.