Synthesis and Photovoltaic Properties of Formyl End-Capped Oligothiophenes

For the purpose of developing novel photovoltaic materials, 5,5″-biformyl-2,2′:5′,2″-terthiophene (OHC-3T-CHO) and 5,5″″-biformyl-2,2′:5′,2″:5″,2″′:5″′,2″″-q-uinquethiophene (OHC-5T-CHO) were synthesized. The photovoltaic properties of OHC-3T-CHO and OHC-5T-CHO were studied. We have fabricated two flexible organic photovoltaic devices using OHC-3T-CHO, OHC-5T-CHO, and 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA). The PET-ITO (indium tin oxides coated with polyethylene terephthalate)/OHC-3T-CHO/PTCDA/Al device has an open circuit voltage (V _oc ) of 1.12 V, and photoelectric conversion efficiency (PCE) of 1.00%, whereas the PET-ITO/OHC-5T-CHO/PTCDA/Al device has a V _oc of 1.78 V and PCE of 1.08%. Both devices have high V _oc (1.12 V and 1.78 V). It is possible that intermolecular hydrogen bonding between the –CHO group of OHC-nT-CHO and the carboxylic dianhydride of PTCDA enhanced the efficiency by promoting forward interfacial electron transfer.