An asymmetric small molecule based on thieno[2,3-f]benzofuran for efficient organic solar cells

• An asymmetric small molecule R3T-TBFO was designed and synthesized.
• R3T-TBFO film showed a wide absorption range from 300 nm to 763 nm, with a low optical bandgap of 1.63 eV.
• The device with TA + SVA treatment presented a better balanced hole- and electron-mobility.
• The TA + SVA based device exhibited a PCE of 6.32%, with a high FF of 0.72.

A new asymmetric small molecule, named R3T-TBFO, with 4,8-bis(2-ethylhexyloxy)-substituted thieno[2,3-f]benzofuran (TBF) as central donor block, has been synthesized and used as donor material in organic solar cells (OSCs). With thermal annealing (TA) and solvent vapor annealing (SVA) treatment, the blend of R3T-TBFO/PC71BM shows a higher hole mobility of 1.37 × 10−4 cm2 V−1 s−1 and a more balanced charge mobilities. Using a structure of ITO/PEDOT:PSS/R3T-TBFO:PC71BM/ZrAcac/Al, the device with TA treatment delivered a moderate power conversion efficiency (PCE) of 5.63%, while device after TA + SVA treatment showed a preferable PCE of 6.32% with a high fill factor (FF) of 0.72.

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