Novel thienoisoindigo-based dyes for near-infrared organic photovoltaics - A combination of theoretical and experimental study

A series of thienoisoindigo (TII)-based dyes (TII 1–4) using different electron-donating moieties (D) and π-linkers were synthesized. The experimental results show that the maximum absorption band of TII 1–4 was located at 611–749 nm. Moreover, their absorption onset was extended to 741–901 nm that covers the near infrared (NIR) region. The bulk-heterojunction solar cell device fabricated by using TII 3/PC61BM as the active layer exhibited a power conversion efficiency (PCE) of 0.82%, showing the potential of TII-based dyes for NIR organic photovoltaics (OPVs). In order to study the structural effect of dyes on the PCE of solar cells, we further designed four TII-based dyes (TII 5–8) and the photophysical and photovoltaic properties for TII 1–8 were investigated through theoretical calculations. Calculated results demonstrate that carbazole group, whose has strong electron-donating ability than D moieties in this study, leads to generate long lifetime of the first excited state and whose generate large short-circuit current (Jsc). Thiophene group, whose has weak resonance energy than other π-linkers, can improve the π delocalization effect throughout whole molecule and generate large open-circuit voltage (Voc). According to these results, TII 3 and TII 8 with the carbazole as D moiety and thiophene as π-linker should be useful in development of a new SM-OPV device.