Identification of the limiting factors for high-temperature GaAs, GaInP, and AIGalnP solar cells from device and carrier lifetime analysis

摘要

We analyze the temperature-dependent dark saturation current density and open-circuit voltage (V_(OC)) for GaAs, GalnP, and AIGalnP solar cells from 25 to 400 ℃. As expected, the intrinsic carrier concentration, n_i„ dominates the temperature dependence of the dark currents. However, at 400 ℃, we measure V_(OC) that is ~50 mV higher for the GaAs solar cell and ~60-110 mV lower for the GalnP and AIGalnP solar cells compared to what would be expected from commonly used solar cell models that consider only the n_i ~2 temperature dependence. To better understand these deviations, we measure the carrier lifetimes of p-type GaAs, GalnP, and AIGalnP double heterostruc-tures (DHs) from 25 to 400 ℃ 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 ℃ to 400 ℃. In contrast, we find that thermionic emission dominates for the GalnP and AIGalnP 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 ℃ to 400 ℃. These observations suggest that optimization of the minority carrier confinement layers for the GalnP and AIGalnP solar cells could help to improve V_(OC) and solar cell efficiency at elevated temperatures. We demonstrate V_(OC) improvement at 200-400 ℃ in GalnP solar cells fabricated with modified AIGalnP window and back surface field layers.