Nanoscale engineering: optimizing electron-hole kinetics of quantum dot solar cells

We report the substantial increase in power efficiency in InAs/GaAs quantum dot (QD) solar cells due to n-doping of the inter-dot space in p+--n+structures and investigate the physical mechanisms that provide this significant improvement. We have compared the GaAs reference cell to undoped, n-doped and p-doped QD solar cell structures and found that the short circuit current, JSC, of the undoped QD solar cell is comparable to that of the GaAs reference cell. On the other hand, while p-doping deteriorates the device performance, n-doping significantly increases JSCwithout degradation of the open circuit voltage, VOC. The photovoltaic device, n-doped to provide approximately six electrons per dot, demonstrates 60% increase in JSC, from 15.07 mA/cm2to 24.30 mA/cm2. Strong increase in the photoresponse and JSCof the IR portion of the solar spectrum has been observed for the n-doped structures. From the photoluminescence data, the electron capture noticeably dominates over hole capture leading to an accumulation of electrons in the dots. We have observed that QDs with built-in charge (Q-BIC) enhances harvesting of IR energy, suppresses the fast electron capture process, and stabilizes the open circuit voltage. All of these factors lead to a significant improvement of the cell efficiency.