Engineering of Nanoscale Barriers for Enhanced Energy Conversion in Quantum Dot Solar Cells

Nanostructured materials provide various mechanisms of photovoltaic conversion broadband solar spectrum in a single-junction solar cell. Quantum Dot Solar Cells (QDSC) are a promising candidate to exceed the fundamental Shockley-Queisser limit on photovoltaic conversion efficiency due to the unique carrier dynamics. Two-Step Photon Absorption (TSPA) is the core of multistep processes in QDs. One of the challenges in QDSC is the additional recombination centers introduced along with the implementation of quantum dots. Nanoscale potential barriers and nanoscale band engineering are effective ways to suppress photoelectron capture into QDs. Selective doping creates a built-in charge (BIC) in the QDs and forms potential barriers around the QDs. QDs enable photovoltaic conversion of below-bandgap photons via intermediate localized states. The above-bandgap photon extraction of electrons from QDs via Coulomb interaction induced by hot electrons is enhanced.;In this work, to study the effects of nanoscale potential profile and nanoscale band engineering, Gallium Arsenide (GaAs) solar cell devices with various Indium Arsenide (InAs) QD media and selective doping were fabricated. QD media and wetting layer (WL) provide substantial enhancement in infrared (IR) conversion. In devices with 40 QD layers the short circuit current density reached 29.2 mA/cm2. All QD devices achieved conversion efficiency of 18-19% under 1-Sun AM1.5G solar spectrum. Conversion efficiency of 21.6% was obtained in the range of 40-90 suns. The two-diode model revealed that Shockley-Read Hall (S-R-H) recombination losses are significantly reduced in devices with doped QDs.