Flexible organic photovoltaic devices based on oligothiophene derivatives

For the purpose of developing flexible organic photovoltaic devices, we have fabricated two flexible devices using 5-formyl-2,2′:5′,2″:5″,2‴-quaterthiophene (4T-CHO), 5-formyl-2,2′:5′, 2″:5″,2‴:5‴,2⁗-quinquethiophene (5T-CHO) and 3,4,9,10-perylenetertracarboxylic dianhydride (PTCDA). The PET-ITO/4T-CHO/PTCDA/Al device has an open circuit voltage (Voc) of 1.56 V, photoelectric conversion efficiency of 0.77%. The PET-ITO/5T-CHO/PTCDA/Al device has a Voc of 1.70 V, photoelectric conversion efficiency of 0.84%. The two flexible devices have high Voc (1.56 and 1.70 V). It is possible that intermolecular hydrogen bonding between –CHO group of nT-CHO and carboxylic dianhydride of PTCDA contributes to enhancing the efficiency by promoting interfacial electron transfer and eliminating the subconducting band trap sites.