Identification of the Limiting Factors for High-Temperature GaAs, GaInP, and AlGaInP Solar Cells from Device and Carrier Lifetime Analysis

We analyze the temperature-dependent dark saturation current density and open-circuit voltage (V_OC) for GaAs, GaInP, and AlGaInP solar cells from 25 to 400 °C. As expected, the intrinsic carrier concentration, n_i, dominates the temperature dependence of the dark currents. However, at 400 °C, we measure V_OC that is ∼50 mV higher for the GaAs solar cell and ∼60-110 mV lower for the GaInP and AlGaInP solar cells compared to what would be expected from commonly used solar cell models that consider only the n_i² temperature dependence. To better understand these deviations, we measure the carrier lifetimes of p-type GaAs, GaInP, and AlGaInP double heterostructures (DHs) from 25 to 400 °C using time-resolved photoluminescence. Temperature-dependent minority carrier lifetimes are analyzed to determine the relative contributions of the radiative recombination, interface recombination, Shockley-Read-Hall recombination, and thermionic emission processes. We find that radiative recombination dominates for the GaAs DHs with the effective lifetime approximately doubling as the temperature is increased from 25 °C to 400 °C. In contrast, we find that thermionic emission dominates for the GaInP and AlGaInP DHs at elevated temperatures, leading to a 3-4× reduction in the effective lifetime and ∼40× increase in the surface recombination velocity as the temperature is increased from 25 °C to 400 °C. These observations suggest that optimization of the minority carrier confinement layers for the GaInP and AlGaInP solar cells could help to improve V_OC and solar cell efficiency at elevated temperatures. We demonstrate V_OC improvement at 200-400 °C in GaInP solar cells fabricated with modified AlGaInP window and back surface field layers.