Dielectric constant (ε) is an important parameter affecting the power conversion efficiency of organic solar cells (OSC).Increasing e of bulk heterojunctions in general can benefit the performance of OSCs,as an increased ε will reduce the influence of Coulomb interaction between weakly bound electron-hole pairs on charge-transfer states or bimolecular recombination involving mobile carriers to reduce geminate and nongeminate losses.In this review,we overview the current understandings on dielectric constant and its impacts on exciton dissociation and voltage losses in OsCs and summarize recent efforts attempting to modify the dielectric properties of OSC materials through synthetic approaches.We further discuss the commonly adopted techniques for determining the parameter of ε with stressing the testing conditions that may affect the accuracy of results.At last,we suggest that novel experimental methods to improve the dielectric constant and resultant physical processes in OSCs will be appreciated,which helps enrich the existing strategy reservoir toward enhancement of photovoltaic efficiencies.