Ground- and excited-state characteristics in photovoltaic polymer N2200

As a classical polymer acceptor material, N2200 has received extensive attention and research in the field of polymer solar cells (PSCs). However, the intrinsic properties of ground- and excited-states in N2200, which are critical for the application of N2200 in PSCs, remain poorly understood. In this work, the ground- and excited-state properties of N2200 solution and film were studied by steady-state and time-resolved spectroscopies as well as time-dependent density functional theory (TD-DFT) calculations. The transition mechanism of absorption peaks of N2200 was evaluated through the natural transition orbitals (NTOs) and hole-electron population analysis by TD-DFT. Time-resolved photoluminescence (TRPL) study shows that the lifetimes of singlet excitons in N2200 chlorobenzene solution and film are similar to 90 ps and similar to 60 ps, respectively. Considering the absolute quantum yield of N2200 film, we deduce that the intrinsic lifetime of singlet exciton can be as long as similar to 20 ns. By comparing the TRPL and transient absorption (TA) kinetics, we find that the decay of singlet excitons in N2200 solution is dominated by a fast non-radiative decay process, and the component induced by intersystem crossing is less than 5%. Besides that, the annihilation radius, annihilation rate and diffusion length of singlet excitons in N2200 film were evaluated as 3.6 nm, 2.5 x 10(-9) cm(3) s(-1) and 4.5 nm, respectively. Our work provides comprehensive information on the excited states of N2200, which is helpful for the application of N2200 in all-PSCs.

Automated summary

The ground- and excited-state properties of N2200 solution and film were studied, along with the transition mechanism of absorption peaks. TRPL study showed similar lifetimes of singlet excitons in N2200 chlorobenzene solution and film, and it was deduced that the intrinsic lifetime of singlet exciton could be as long as about 20 ns. By comparing TRPL and TA kinetics, it was found that the decay of singlet excitons in N2200 solution is dominated by a fast non-radiative decay process.