Application of small molecules based on a dithienogermole core in bulk heterojunction organic solar cells and perovskite solar cells

We report the synthesis and characterization of a dithienogermole (DTGe) based small molecule, named Ge-PO-2CN, as a donor material for bulk heterojunction (BHJ) organic solar cells (OSCs) and as a hole transport material (HTM) for dopant-free perovskite solar cells (PSCs). This molecule consists with a high planar and electron rich DTGe core as a central core unit and covalently linked with an electron rich phenoxazine group. Finally, it is end-capped with electron-deficient malononitrile group. This molecule was synthesized by a facile synthetic protocol, without using costly and complicated purification techniques. The Ge-PO-2CN compound has a suitable HOMO level with respect to the valence band of the perovskite absorber and the BHJ OSCs. The BHJ OSC device made with Ge-PO-2CN as the donor and PC71BM as an acceptor results in a power conversion efficiency (PCE) of 5.4%. Subsequently, the PSC with an active area of 1.02 cm2 constructed with dopant-free Ge-PO-2CN as an HTM achieved a PCE of up to 11.63%.