In this study, the Cs adsorption behavior on n-type 3C-SiC (0001)-(2 x 1) and -(3 x 2) reconstructed surfaces are investigated via first-principles calculations. The potentiality of 3C-SiC as the anode material of solar cell based on photon-enhanced thermionic emission (PETE) is discussed. Various doping configurations are considered for the determination of an optimum n-type doping structure. Cs-covered (3 x 2) surface exhibits stronger stability compared with (2 x 1) surface. The charge transfer caused by Cs adsorption produces a [Cs+-SiC] dipole moment directing from Cs adatom to reconstructed surface, resulting in an effective declination of work function. Specifically, 0.5 ML Cs coverage surface provides an ultralow work function with 0.9 eV, demonstrating its potential application in PETE devices. Combining with a photoemission model, the maximum conversion efficiency can attain 30% utilizing SiC as an anode. Moreover, the Mulliken charge analysis provides the details of surface charge transfer and implies the inner mechanism of work function alteration. This study provides guiding significance for the synthesis of SiC material with low work function and an effective theoretical method for the design of high-performance anode materials in application of PETE devices. The adsorption mechanism of Cs on n-type doped 3C-SiC(0001)-(2 x 1) and -(3 x 2) reconstructed surfaces and its application as the anode material of solar cell are systematically investigated. For one Cs adatom adsorption, Cs-covered (3 x 2) surfaces present stronger stability compared with (2 x 1) surfaces. Cs-decorated (3 x 2) surface with 0.5 ML coverage exhibits an ultralow work function as low as 0.9 eV. Based on the photoemission model, the maximum conversion efficiency of PETE devices with SiC anode can reach 30%.