Following the TRMC Trail: Optimization of Photovoltaic Efficiency and Structure-Property Correlation of Thiophene Oligomers.
Semiconducting conjugated oligomers having same end group (N-ethylrhodanine) but different central core (thiophene: OT-T, bithiophene: OT-BT, thienothiophene: OT-TT) connected through thiophene pi-linker (alkylated terthiophene) were synthesized for solution processable bulk-heterojunction solar cells. The effect of the incorporation of an extra thiophene to the central thiophene unit either through C-C bond linkage to form bithiophene or by fusing two thiophenes together to form thienothiophene on the optoelectronic properties and photovoltaic performances of the oligomers were studied in detail. Flash photolysis time-resolved microwave conductivity (FP-TRMC) technique shows OT-TT has significantly higher photoconductivity than OT-T and OT-BT implying that the former can outperform the latter two derivatives by a wide margin under identical conditions in a bulk-heterojunction solar cell device. However, the initial photovoltaic devices fabricated from all three oligomers (with PC71BM as the acceptor) gave power conversion efficiencies (PCEs) of about 0.7%, which was counterintuitive to the TRMC observation. By using TRMC results as a guiding tool, solution engineering was carried out; no remarkable changes were seen in the PCE of OT-T and OT-BT. On the other hand, 5-fold enhancement in the device efficiency was achieved in OT-TT (PCE: 3.52%, VOC: 0.80 V, JSC: 8.74 mA cm(-2), FF: 0.50), which was in correlation with the TRMC results. The structure-property correlation and the fundamental reasons for the improvement in device performance upon solvent engineering were deduced through UV-vis absorption, atomic force microscopy, bright-field transmission electron microscopy, photoluminescence quenching analysis and two-dimensional grazing incidence X-ray diffraction studies.
Photosciences and Photonics Section, CSIR-National Institute for Interdisciplinary Science and Technology (NIIST) , Trivandrum 695019, Kerala India.|Academy of Scientific and Innovative Research (AcSIR) , New Delhi 110 001, India.
Tanwistha
T
Ghosh
Department of Applied Chemistry, Graduate School of Engineering, Osaka University , 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
Anesh
A
Gopal
Department of Applied Chemistry, Graduate School of Engineering, Osaka University , 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
Shinji
S
Nagasawa
Photosciences and Photonics Section, CSIR-National Institute for Interdisciplinary Science and Technology (NIIST) , Trivandrum 695019, Kerala India.
Nila
N
Mohan
Department of Applied Chemistry, Graduate School of Engineering, Osaka University , 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
Akinori
A
Saeki
Photosciences and Photonics Section, CSIR-National Institute for Interdisciplinary Science and Technology (NIIST) , Trivandrum 695019, Kerala India.|Academy of Scientific and Innovative Research (AcSIR) , New Delhi 110 001, India.
Chakkooth
C
Vijayakumar
Donor−acceptor systems; Photovoltaics; Structure−property correlation; Thiophene oligomers; Time-resolved microwave conductivity