Understanding the effects of the chemical structures of donor polymers on the photovoltaic properties of their corresponding organic photovoltaic (OPV) devices under various light-intensity conditions is important for improving the performance of these devices. We synthesized a series of copolymers based on poly[(2,6-(4,8-bis(5-(2-thioethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione))] (PBDB-TS) and studied the effects of chlorine substitution of its thiophene-substituted benzodithiophene (BDT-Th) unit on its photovoltaic properties. Chlorination of the polymer resulted in a bulk heterojunction (BHJ) morphology optimized for efficient charge transport with suppressed leakage current and an increased open-circuit voltage of the OPV device; this optimization led to a remarkable enhancement of the OPV device's power conversion efficiency (PCE) not only under the condition of 1 sun illumination but also under a low light intensity mimicking indoor light; the PCE increased from 8.7% for PBDB-TS to ∼13% for the chlorinated polymers, PBDB-TS-3Cl, and PBDB-TS-4Cl under the 1 sun illumination condition and from 5.3% for PBDB-TS to 21.7% for PBDB-TS-4Cl under 500 lx fluorescence illuminance. Interestingly, although the OPV PCEs under 1 sun illumination were independent of the position of chlorine substitution onto the polymer, PBDB-TS-4Cl exhibited better performance under simulated indoor light than its derivative PBDB-TS-3Cl. Our results demonstrate that efficient light absorption and charge-carrier generation play key roles in achieving high OPV efficiency under low-light-intensity conditions.
Bibliographical noteFunding Information:
This research was financially supported by the National Research Foundation of Korea (NRF) funded by the Korea Government (MSIP) (2018R1A2A1A05078734), the Korea Evaluation Institute of Industrial Technology (KEIT) and the Ministry of Trade, Industry & Energy (MOTIE, Korea) (No. 20173010013000), the Basic Research in Science & Engineering Program of the National Research Foundation of Korea (NRF-2019R1A2C2088022), and the KIST Institutional Program (2E30150). This research was also spported by Technology Development Program to Solve Climate Changes through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (2019M1A2A2072412).
© 2020 American Chemical Society.
- bulk heterojunction
- chlorine substitution
- indoor light
- organic photovoltaic
ASJC Scopus subject areas
- Materials Science(all)