Thin-film solar thermoelectric generators show much promise in effective use of solar energy as a power supply for microscale devices. In this paper, we fabricated a flexible thin-film solar thermoelectric generator on the polyimide substrate using simple mask-assisted deposition process. The p-type Bi0.5Sb1.5Te3 and n-type Bi2Te2.7Se0.3 thermoelectric films with special hierarchical nanostructure were prepared, resulting in substantial improvement in the electrical conductivity. The solar thermoelectric generator with the hierarchical Bi-Te thin films is able to generate 220 mV of the output voltage and 80 mu W of the maximum power for a temperature difference of 100 K. We also analyzed the optimized design for the solar thermoelectric generator. By employing a package for the thermoelectric legs and a perforated structure, the heat flow was restricted along the thermoelectric legs and a larger temperature difference was achieved. A fast electrical response to the on-off simulated solar light irradiation was also observed, indicating light sensing feature of the fabricated thin-film solar thermoelectric generator. Our results revealed that a remarkably enhanced output power has been achieved in the flexible thin-film solar thermoelectric generator due to the introduction of the improved thermoelectric films and the optimized thermal design. (C) 2015 Elsevier Ltd. All rights reserved.