Aggregation Optimization by Molecular Engineering of D18-Based Terpolymer for Highly Efficient Indoor Organic Solar Cells

Indoor organic solar cells (IOSCs), which harvest ambient light for electricity generation, are a highly promising power source for emerging technologies such as the rapidly growing number of low-power electronics and the Internet of Things. The aggregation and phase separation of polymer donors are critical for charge transport and trap-assisted recombination properties of their active blends with electron acceptors that determine the efficiency of IOSCs. In this work, we synthesized a series of terpolymers (D18BTSTX) with different molar ratios by partially replacing the D18 backbone with a rigid and polarizable π-bridge unit. D18BTST0.4 terpolymer improves morphological features in the photoactive layer and suppresses charge recombination loss while maintaining a wide bandgap to match the indoor solar spectrum. As a result, D18BTST0.4:FCC-Cl achieves excellent indoor efficiency of 22.41% with a Jsc of 226.19 μA cm–2 and a Voc of 0.98 V under a 2700 K LED at 2000 lx, benefiting from the solid-state packing and phase separation in blend films compared to the D18:FCC-Cl model devices (iPCE 18.02%). Our work reveals an interesting rational material design for finely tuned electrochemical and morphological characteristics to overcome the current limitations of D18-based IOSCs.