Improved photovoltaic performance of D-A-D-type small molecules with isoindigo and pyrene units by inserting different π-conjugated bridge

Two novel D-π-A-π-D-type small molecules (SMs) of IID(Ac-Py)2 and IID(Th-Py)2 were synthesized and characterized. Significantly improved photophysical and photovoltaic performances were observed for both SMs containing extended π-bridge in comparison with those for their parent D-A-D type molecule of IID(Py)2. A maximum power conversion efficiency (PCE) of 1.88% was obtained in the IID(Th-Py)2/PC71BM-based solar cells. Particularly, the IID(Th-Py)2/PC61BM-based device exhibited a Voc value up to 1.01 V, which is among the highest values in literature for solution processed SMs OSCs without any post processing.