OBSERVATION OF PHOTON RECYCLING IN STRAIN-BALANCED QUANTUM WELL SOLAR CELLS

摘要

Suppression of dark currents in distributed Bragg reflector (DBR) strain-balanced quantum well solar cells (SB-QWSC) due to photon recycling (PR) can lead to increased device efficiency at high concentrator levels. At high bias or concentration the primary recombination mechanism in SB-QWSCs is radiative recombination in the quantum wells, which can be re-absorbed in the device significantly reducing the ideality n=1 dark current component. PR can be achieved by placing a distributed Bragg reflector (DBR) at the rear surface of the solar cellsuch that photons emitted from the device through radiative recombination may be trapped in the device leading tophoton re-absorption. In this paper we will present results, for the first time, showing the effects of PR in theelectroluminescence (EL) spectra of SB-QWSCs. Furthermore, improved modeling results comparing the radiativeideality n=1 dark currents from SB-QWSC devices grown on DBR structures with varying numbers and depths ofquantum wells are presented. Comparison is made with control cells lacking a DBR. These results convincinglydemonstrate the PR effect and we make predictions for efficiency enhancement in optimised SB-QWSC devices.