Apparatus and methods of generating electricity include using an optically and thermally responsive material comprising single-walled Carbon nanotubes and Copper sulfide nanoparticles. This material acts as a thermoelectric generator lacking rectifying effects. In some forms, the generator may generate electricity from a light source alone, a heat source alone, or a source of both light and heat. Some forms exhibit enhanced optical and thermal switching characteristics, light absorption, photocurrent and thermocurrent generation under light illumination or/and thermal radiation, providing a new route to obtain thermoelectricity without any cooling or heat-sink component. Moreover, measurements showed thin films of SWNT CuS NPs had significantly increased light absorption (up to 80%) compared to untreated SWNT thin films.