Efficient Solution‐Processed Bulk Heterojunction Solar Cells by Antiparallel Supramolecular Arrangement of Dipolar Donor–Acceptor Dyes

A series of dipolar donor–acceptor (D –A) chromophores with aminothiophene donor and different heterocyclic acceptor units is reported. By modulation of the acceptor strength, absorption bands over the whole visible spectrum are accessible as well as adjustment of the frontier molecular orbital levels. The performance of the chromophores in blends with fullerene acceptors in solution‐processed bulk heterojunction solar cells was studied and related to the molecular properties of the dyes. In particular, the effect of the large ground‐state dipole moments of these dyes was investigated by single crystal X‐ray analysis, which revealed antiparallel dimers, resulting in an annihilation of the dipole moments. This specific feature of supramolecular organization explains the excellent performance of merocyanine dyes in organic solar cells. With blends of HB366 :PC₇₁BM, the most efficient solar cell with a V_OC of 1.0 V, a J_SC of 10.2 mA cm⁻², and a power‐conversion efficiency of 4.5 % was achieved under standard AM1.5, 100 mW cm⁻² conditions. Under reduced lighting conditions, even higher efficiencies up to 5.1 % was obtained.