Ultrafast charge transfer and suppressed non-radiative energy loss enabled by trifluoromethyl-substituted low-cost polymer donors for efficient organic solar cells

The exorbitant price of photoactive materials is a huge challenge for the industrialization of organic solar cells (OSCs). To address this, two simple-structure PTQ derivative polymer donors PTQ14 and PTQ15 with trifluoromethyl (CF3) substituent are designed and synthesized. Both polymers show low-cost advantage with estimated cost-per-kilogram of about 35.00x10(3) $ kg(-1), which is only one-fifth to one-sixth of reported high-performance polymer donors. The introduction of CF3 group significantly shifts down the energy levels of the two polymer donors and induces tighter and more long-range ordered molecular self-assembly of pi-pi packing of PTQ15. Remarkedly, the PTQ15-based ternary OSCs achieves ultrafast and efficient charge transfer within 1.40 ps, which is significantly faster than its counterparts (14.54 and 10.17 ps). Meanwhile, this device exhibits reduced voltage loss of 0.506 V due to suppressed non-radiative loss of only 0.190 eV. As a result, an impressive efficiency of 19.96% is achieved, which is the highest value of OSCs based on low-cost organic photovoltaic materials, and a record efficiency of 19.37% for open-air processed OSCs is also obtained. More importantly, this device shows high cost-effectiveness for industrialization with low minimum sustainable price of only 0.36 $ W-p(-1), which is the lowest value for organic photovoltaics so far.