A new approach for preparation of ternary bulk-heterojunction using dual-feed ultrasonic spray for organic solar cells

Abstract Ternary bulk heterojunctions using a wide band gap polymer P3HT and a narrow band gap polymer PTB7 as donors and ICBA as acceptor have been fabricated using a novel dual-feed approach in an ultrasonic spray. The binary blend of two donor polymers in a BHJ formed by a conventional method in which the two donor polymers are mixed intimately in a common solvent may lead to unfavourable phase morphology due to unfavourable interaction between them and puts constraints on the composition of the polymer blend in the BHJ. The unfavourable interaction may cause severe molecular disorder leading to charge recombination trap site, and thereby decreases the device performance. In the new method proposed in this paper intimate mixing of two donor polymers is avoided, which removes the constraint on the fraction of second donor in the first. Moreover, it also results in better polymer ordering leading to significantly higher hole mobility compared to that achieved with conventional method. The steady state photoluminescence study depicts more efficient FRET in P3HT:PTB7 binary blend prepared with dual channel method as compared to that prepared with single channel mode. With this method, ternary BHJ can be prepared even with higher concentration of the third component to have maximum power absorption, without compromising its optoelectronic properties. Although the superior properties of BHJ formed with the new dual-feed method did not reflected in similar performance in device functioning, with better choice of the donors and acceptor and with more control on nanoscale morphology through selection of proper solvents the device performance may improve to acceptable level. This report opens a new way of BHJ preparation in ternary organic solar cell fabrication.