Linkage effects of linear D–π–A–π–D type diketopyrrolopyrrole-triphenylamine based solution-processable organic small molecule photovoltaic materials

Four novel D- pi -A- pi -D-type small molecules (SMs) were synthesized and their pi -linkage effects were investigated. Among them, SM2 with vinylene as the pi -linkage exhibited better molecular coplanarity, reaching a relatively higher power conversion efficiency (PCE) of 3.76%. SM3 and SM4 with acetylene and acrylonitrile as pi -linkages exhibited relatively higher open-circuit voltages (V sub(OC)) of 0.93 V and 0.90 V, respectively, owing to their deep-lying HOMO levels. These results gave an important guide for developing new materials in solution-processed small molecule solar cells.