Gradient-Doped Colloidal Quantum Dot Solids Enable Thermophotovoltaic Harvesting of Waste Heat

Electromagnetic radiation emitted from hot objects represents a sizable source of energy, one that in most applications is not harvested efficiently. Even for a blackbody at 800 degrees C, the radiation intensity peaks near 2.7 mu m wavelength, and this requires a semiconductor absorber having a band gap in the short-wavelength infrared and beyond to enable thermophotovoltaic (TPV) heat recovery. Here we report the first solution-processed TPV device to harvest efficiently 800 degrees C heat. The active layer consists of colloidal quantum dots (CQDs), infrared-absorbing nanoparticles synthesized using a scalable solution-based method, having 0.75 eV band gap. We construct rectifying junction devices based on controllably p- and n-doped CQD solids that benefit from a gradient in electron affinity that extends over the devices' thickness. The gradient doped architecture relies on engineered charge carrier drift and overcomes the existing limitations of small band gap CQD solids. The devices provide 2.7% efficiency in the conversion of optical power from above-band gap photons from a blackbody source at 800 +/- 20 degrees C into electrical power. The cells were thermally stable up to 140 degrees C, increasing the promise of CQD solids for TPV applications.