Long-term Thermal Stability of High-Efficiency Polymer Solar Cells Based on Photocrosslinkable Donor-Acceptor Conjugated Polymers

Recently, the long-term stability of organic photovoltaic (OPV) devices has been recognized as an important area of research. Here, we report the first study on the thermal stability of OPV devices based on a donor-acceptor p-type copolymer. We have synthesized a photocrosslinkable version of a thieno[3,4-c]pyrrole-4,6-dione (TPD)-based polymer by incorporating TPD monomers with a bromide-functionalized side chain. By synthetically tuning the amount of Br-units in the polymer and by employing UV-light-mediated photocrosslinking, we were able to fabricate OPV devices with stable power conversion efficiencies (PCE) as high as 4.7% after 72 hours of thermal annealing at 150°C. In contrast, without complete photocrosslinking, the polymer device performances deteriorated upon annealing, showing no thermal stability. This study demonstrates the highest device PCE reported for OPV systems subjected to long-term thermal annealing at high temperatures.