Novel Third Components with (Thio)barbituric Acid as the End Groups Improving the Efficiency of Ternary Solar Cells

Efficient soluble PTCBI-type non-fullerene acceptor materials for organic solar cells

Single perylene diimide (PDI) used as a non-fullerene acceptor (NFA) in organic solar cells (OSCs) is enticing because of its low cost and excellent stability. To improve the photovoltaic performance, it is vital to narrow the bandgap and regulate the stacking behavior. To address this challenge, we synthesize soluble perylenetetracarboxylic bisbenzimidazole (PTCBI) molecules with a bulky side chain at the bay region, by replacing the widely used "swallow tail" type alkyl chains at the imide position of PDI molecules with a planar benzimidazole structure. Compared with PDI molecules, PTCBI molecules exhibit red-shifted UV-vis absorption spectra with larger extinction coefficient, and one magnitude higher electron mobility. Finally, OSCs based on one soluble PTCBI-type NFA, namely MAS-7, exhibit a champion power conversion efficiency (PCE) of 4.34%, which is significantly higher than that of the corresponding PDI-based OSCs and is the highest PCE of PTCBI-based OSCs reported. These results highlight the potential of soluble PTCBI derivatives as NFAs in OSCs.

Chlorinated Narrow Bandgap Polymer Suppresses Non-Radiative Recombination Energy Loss Enabling Perylene Diimides-Based Organic Solar Cells Exceeding 10% Efficiency

The scarcity of narrow bandgap donor polymers matched with perylene diimides (PDI)-based nonfullerene acceptors (NFAs) hinders improvement of the power conversion efficiency (PCE) value of organic solar cells (OSCs). Here, it is reported that a narrow bandgap donor polymer PDX, the chlorinated derivative of the famous polymer donor PTB7-Th, blended with PDI-based NFA boosts the PCE value exceeding 10%. The electroluminescent quantum efficiency of PDX-based OSCs is two orders of magnitude higher than that of PTB7-Th-based OSCs;therefore, the nonradiative energy loss is 0.103 eV lower. This is the highest PCE value for OSCs with the lowest energy loss using the blend of PTB7-Th derivatives and PDI-based NFAs as the active layer. Besides, PDX-based devices showed larger phase separation, faster charge mobilities, higher exciton dissociation probability, suppressed charge recombination, elevated charge transfer state, and decreased energetic disorder compared with the PTB7-Th-based OSCs. All these factors contribute to the simultaneously improved short circuit current density, open circuit voltage, and fill factor, thus significantly improving PCE. These results prove that chlorinated conjugated side thienyl groups can efficiently suppress the non-radiative energy loss and highlight the importance of fine-modifying or developing novel narrow bandgap polymers to further elevate the PCE value of PDI-based OSCs.