Small Molecular Donors for Organic Solar Cells Obtained by Simple and Clean Synthesis

A small donor–acceptor molecule is synthesized in a two‐step procedure involving reaction of N , N ‐diphenylhydrazine on 2,5‐diformylthiophene and Knoevenagel condensation. Results of UV/Vis absorption spectroscopy and cyclic voltammetry show that replacement of the phenyl ring bridge of a reference compound 2 by an azo group produces a slight red‐shift of λ max , an enhancement of the molecular absorption coefficient, and a decrease of the energy level of the frontier orbitals. A preliminary evaluation of the potentialities of compound 1 as donor material in a basic bilayer planar heterojunction cell of 28 mm 2 active area using C 60 as acceptor gave a short‐circuit current density of 6.32 mA cm −2 and a power conversion efficiency of 2.07 %.