Synthesis of a selenium and germanium containing random copolymer as an acceptor for all-polymer solar cells

For the need of electron-transporting and electron-affinity materials, n-type polymers (as acceptor) have gained a lot of attention recently. We have synthesized a selenium and germanium containing copolymer as the acceptor for all-polymer solar cells (all-PSCs). The copolymer has larger p-orbital selenium and germanium atoms for more electron transition from pi to pi* to enlarge light harvest of polymer. To prepare the copolymer, a monomer containing d-orbital atom, selenium, was first synthesized from low-cost starting materials. A random copolymer was prepared from the monomer with a commercial germanium containing monomer via palladium catalyzed Stille coupling reaction. Taking the side-chain effect into account, we incorporated dodecyloxy group to increase the solubility of the polymer and also increase the coplanarity by oxygen–sulfur (S–O) interaction. Despite the low short-circuit current density (Jsc) value, the random copolymer with 3d-orbital electrons has the potential to be the candidate for n-type material. In comparison, we also fabricated P3HT/PffBT4T-2OD all-PSCs, acquiring PCE of about 0.5% without any additive. POLYM. ENG. SCI., 58:387–394, 2018.