  The thermophotovoltaic cells which can convert the infrared radiation from
room-temperature surroundings into electricity are of significance due to their
potential applications in many fields. In this work, narrow bandgap
Bi2Te3/Sb2Te3 thin film thermophotovoltaic cells were fabricated, and the
formation mechanism of Bi2Te3/Sb2Te3 p-n heterojunctions was investigated.
During the formation of the heterojunctions at room temperature, both electrons
and holes diffuse in the same direction from n-type Bi2Te3 thin films to p-type
Sb2Te3 thin films rather than conventional bi-directional diffusion. Because
the strong intrinsic excitation generates a large number of intrinsic carriers
which weaken the built-in electric field of the heterojunctions, their I-V
curves become similar to straight lines. It is also demonstrated that
Bi2Te3/Sb2Te3 thermophotovoltaic cells can output electrical power under the
infrared radiation from a room-temperature heat source. This work proves that
it is possible to convert the infrared radiation from dark and room-temperature
surroundings into electricity through narrow bandgap thermophotovoltaic cells.
