This paper reports Seebeck effects driven by both surface polarization difference and entropy difference by using photoinduced intramolecular charge-transfer states in n-type and p-type conjugated polymers, namely IIDT and IIDDT, respectively, based on vertical conductor/polymer/conductor thin-film devices. We obtain large Seebeck coefficients of -898 μV/K from n-type IIDT and 1300 μV/K from p-type IIDDT when the charge-transfer states are generated by a white light illumination of 100 mW/cm², compared with the values of 380 μV/K and 470 μV/K in dark conditions, respectively. Simultaneously, the electrical conductivities are increased from almost insulating states in dark condition to conducting states under photoexcitation in both n-type IIDT and p-type IIDDT based devices. The large Seebeck effects can be attributed to the following two mechanisms. Firstly, the intramolecular charge-transfer states exhibit strong electron-phonon coupling, which leads to a polarization difference between high and low temperature surfaces. This polarization difference provides an additional driving force to diffuse the charge carriers for the development of Seebeck effects under a temperature gradient. Secondly, the intramolecular charge-transfer states generate majority electrons or holes in the n-type IIDT or p-type IIDDT, ready to be diffused between high and low temperature surfaces for development of the Seebeck effects. Based on surface polarization difference together with entropy difference the intramolecular charge-transfer states can largely enhance the Seebeck effects in the n-type IIDT and p-type IIDDT devices. Furthermore, we find that the Seebeck effects can shift between polarization and entropy regimes when the electrical conductivities are changed by photoexcitation. Therefore, using intramolecular charge-transfer states presents an approach to develop thermoelectric effects in organic materials based on vertical conductor/polymer/conductor thin-film devices.