Efficient photovoltaic performances and enhanced dielectric constants enabled by a fluorinated quinoxaline-based polymer with non-fullerene acceptors

Abstract

Non-fullerene acceptors (NFAs) are widely applied in polymer solar cells (PSCs) to solve the inherent drawbacks like unadjustable energy levels and limited absorptive region of fullerene-based acceptors. The suitable bandgaps with low-lying highest occupied molecular orbital (HOMO) energy levels of the donor materials are two preconditions to achieve highly efficient non-fullerene PSCs. A mono-fluorinated quinoxaline-based alternating polymer ( PBDTTFTQ-DO ) possesses deep HOMO energy level (−5.37 eV) and wide bandgap (1.80 eV), which ensure its potential application as donor material with low bandgap NFAs. To investigate its performances in PSCs with different NFAs, three structurally similar NFAs ( ITIC , ITIC-Th and ITIC-Th1 ) with tunable energy levels and adjustable absorption spectra were selected to match with PBDTTFTQ-DO . It was found that the performances of all three NFAs-based devices were improved to varying degrees after thermal annealing, especially for the PBDTTFTQ-DO : ITIC-Th -based device, a high power conversion efficiency of 7.81% was achieved due to the intensely enhanced film absorption and largely increased dielectric constant after thermal annealing treatment. These results illustrated that the promising performances of quinoxaline-based polymers in NF–PSCs, and what's more, the significant effects of suitable donor-acceptor combination and dielectric constants on the performances of NF–PSCs. • Quinoxaline-based polymer and non-fullerene acceptors were used in solar cells. • High PCE (7.81%) was achieved in polymer:ITIC-Th blend after thermal annealing. • Thermal annealing improved the absorption and dielectric constant of the films.