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-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.