Spectroscopic analysis of InAs quantum dot solar cells

The operation of solar cells incorporating multiple repeat units of InAs quantum dot structures, as well as those with and without d-doping of 4 and 8 electrons per quantum dot, were studied. Room temperature measurements of these samples revealed high quality devices, but insignificant differences between d-doped samples and undoped samples. An IR-pumped quantum efficiency measurement was performed at 6 K to probe the extraction of quantum confined carriers through a two-photon process while shutting off phonon-assisted extraction. No two-photon signal rose above the noise, but additional sub-bandgap illuminated IV curves revealed current generation in the quantum dot devices, suggesting the dominant carrier removal mechanism is through tunneling. Finally, dark-diode data was taken and fit to determine ideality factor as a function of temperature. Control devices had an overall larger ideality, while QD devices exhibited variations as a function of temperature, which were attributed to kinetic barriers in the first QD layers, as well as possible Auger recombination at very low temperature.