The mechanisms of triboelectrification (or contact-electrification) have been debated for many years, with possible mechanisms including electron transfer, ion transfer or the material's species transfer. Recent studies in 2018 using Kelvin probe microscopy and triboelectric nanogenerators revealed that electron transfer is the dominant mechanism for triboelectrification between solid and solid. The work function model can be used to explain electron transfer between a metal and a dielectric. The surface states model can be used to explain electron transfer between two dielectrics. For a general case, since triboelectrification occurs for any material, a generic model has been proposed by Wang, in which the electron transfer is caused by a strong electron cloud overlap between two atoms for the lowered interatomic potential barrier by shortening the bonding length. Based on the model, the effects of temperature and photo excitation on the triboelectrification were investigated. Such model can be further extended to the cases of liquid-solid, liquid-liquid and even gas-liquid.