In this work, a novel solar thermoelectric generator (TEG) design is proposed to enhance its output power and conversion efficiency. It combines segmented thermoelectric materials and asymmetrical legs with variable cross-sectional area along the leg length. A three-dimensional multiphysics thermoelectric model is employed to examine the performance of the new design. The optimal leg length ratio of two segmented materials (P1 and P2 materials) and the optimal cross-sectional area ratio of cold end to hot end are determined. In comparison with using P1 and P2 materials, the results show that the segmented design increases the output power by 14.9% and 16.6%, respectively, when the leg length ratio is optimized. When the asymmetrical legs are introduced to the segmented design, the output power can be additionally increased by 4.21%, as compared with the optimal segmented design. Moreover, a simple analytical model is proposed to predict the optimal leg length ratio of two thermoelectric materials for the present new design. The proposed model can be reduced to the existing models when the leg cross-sectional area ratio of cold end to hot end is equal to 1. Thus, the model can be considered as a generalized model, which can evaluate the optimal leg length ratio for the segmented design with any leg shape. Based on the model, the optimal leg length ratio should make the interface temperature between the two materials equal to the temperature of intersection point of their ZT (figure of merit) curves. Theoretically, this conclusion can be extended to any leg shape with a constant or variable cross-sectional area. The present simulations verify the theoretical prediction of the optimal leg length ratio.