Unusual hot carrier effect and improved carrier extraction observed in asymmetric dilute-nitride quantum-engineered solar cells through photoluminescence (PL) and external quantum efficiency (EQE) measurements

For the full realization of the practical potential of III-V multi-junction devices that incorporate a dilute nitride 1-1.25 eV sub-cell (<40% 1 sun, and <50% at 500X and above), our group, over the past years, have focused on dilute nitride-based devices where the degraded minority carrier diffusion length has a minimal impact on the device performance. We have shown that the incorporation of resonantly coupled GaAsN/GaAs multi-uantum wells in the intrinsic region of p-i-n GaAs cells allows both a significant sub-GaAs-bandgap photon harvesting while maintaining a high open circuit voltage with Woc. Here, in order to gain a better understanding of photo-generated carrier escape and recombination mechanisms in these devices and further optimize the performance, we examine the optical and electrical properties of such devices including with periodic MQWs using various characterization techniques such as: photoluminescence (PL), modulated photo-reflectance (PR), photo-current (PC) as well as current-voltage (IV) measurements under dark or illuminated conditions. The temperature dependent PL analysis enables us to modulate and freezes the carrier thermalization phenomena having extracted activation energies reveal interesting details about carrier escape, intra-cells coupling, and recombination sequences. Extracted electronic temperature of the carriers (about 900K at 300K lattice temperature) from PL measurement reveal more interesting phenomenon on carrier escape and recombination mechanism in both periodic and RTT MQWs solar cell.