High-efficiency InAs/GaAs quantum dot intermediate band solar cell achieved through current constraint engineering

In this work, a novel device concept for improving the efficiency and field operation of conventional InAs/GaAs quantum dot (QD) based intermediate band solar cell (IBSC) with the feature of current constraint (CC-QD-IBSC) was proposed and evaluated from both theoretical simulations and experimental demonstrations. The advantages of the proposed device concept including increasing efficiency, obtaining higher suitability for operation under concentrated photovoltaic (CPV) condition and more robust efficiency stability against intermediate band fluctuation were rigorously identified using the detailed balance theorem by comparing with conventional InAs/GaAs QD-IBSC. Furthermore, a hybrid molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) shuttle growth of the proposed CC-QD-IBSC were adopted in this work for better preserving QD induced intermediate band feature and overcoming practical growth difficulties. By introducing a InGaP top cell for constraining the current of InAs/GaAs QD-IBSC, the short circuit current density of CC-QD-IBSC decreased to 13.0mA/cm2 under 1 sun illumination, a near 50 % reduction compared to the conventional InAs/GaAs QD-IBSC. On the contrary, by well adjusting the regrowth interface between MBE and MOCVD, we managed to reach the highest conversion efficiency of 22.8 % measured at an UL certified laboratory under light concentration ratio of 93 suns for the proposed CC-QD-IBSC with well-functioning QD and IB feature. It is our belief that our results pave the road for developing techniques geared towards higher efficiency and more practical field applications.