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 pi-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 (J(sc)). Thiophene group, whose has weak resonance energy than other pi-linkers, can improve the pi delocalization effect throughout whole molecule and generate large open-circuit voltage (V-oc). According to these results, TII 3 and TII 8 with the carbazole as D moiety and thiophene as pi-linker should be useful in development of a new SM-OPV device.