π-Linkage effect of push-pull-structure organic small molecules for photovoltaic application

Much attention has been paid to the push-pull-structure organic small molecule (OSM) materials for photovoltaic (PV) application in the past decade, due to their facile reduction of energy band gap (E-g) and effective control of PV properties. pi-bridge plays an important role in the push-pull-structure OSMs since an appropriate pi-linkage is crucial for improving the PV performance of organic solar cells (OSCs). In this review, various pi-bridge groups (thiophene, alkene, alkyne, arene and heterocycle) and the pertinent pi-linkage effect will be systematically summarized. These results suggest that the in-depth study of the pi-linkage effect is essential to deeply understanding the relationship between the molecular structure and property, thus improving PV performance.