Optical study of carrier transport in InAs/GaAs quantum dots solar cell

Optical transitions and carrier transport in InAs/GaAs self-assembled quantum dots solar cells (QDSC) were investigated via temperature dependent photoluminescence (TDPL) spectroscopy, charge collection efficiency calculated from bias dependent spectral response, and low temperature photo-current measurements. Band structure simulations were used to calculate the tunneling rate and thermal escape rate of electrons in quantum dots under different bias conditions. It is found that, tunneling rate and thermal escape rate of electrons in the quantum dots increase along p-n direction. From TDPL, compared to test structures, ground state electron activation energy decrease 60 meV in QDSC. TDPL also indicates that electrons are the main carriers escaping from the QD confinement if temperature higher than 120K, while holes are the rate limiting carrier if temperature lower than 120K. Charge collection efficiency is greatly improved above the bulk GaAs absorption edge (870nm) under large reverse bias (-4.5V). Low temperature (20K) bias photocurrent shows that ground state carrier can be collected even at 0.7V forward bias. This indicates that hole tunneling may be dominant at low temperature, or electron experiences tunneling then thermal escape.