Efficient and thermally stable polymer solar cells based on a 54π-electron fullerene acceptor

A 54 pi-electron fullerene acceptor, bis-thieno-o-quinodimethane-methano[60]fullerene (bis-TOQMF), featuring a compact -CH2- addend and two thieno-o-quinodimethane addends, has been developed. Bis-TOQMF possesses good solubility and a high LUMO level of -3.40 eV. Polymer solar cells based on bis-TOQMF/P3HT show not only high V-oc (0.94 V) but also good J(sc) (8.09 mA cm(-2)) and FF (58%). The highest PCE of 4.56% has been achieved for 54 pi-electron fullerene solar cells to date. On the contrary, a 54 pi-electron analogue of bis-TOQMF, tris-thieno-o-quinodimethane-C-60 (tris-TOQC), shows low performance. 1.02% PCE was obtained for tris-TOQC/P3HT solar cells, with high V-oc (0.96 V) but much lower J(sc) (2.85 mA cm(-2)) and FF (35%). Space charge limited current (SCLC) measurements indicate that the electron mobility of bis-TOQMF is 10 times higher than that of tris-TOQC. Bis-TOQMF/P3HT solar cells show higher thermal stability than PC61BM/P3HT solar cells.