Currently, a new generation of ultra-high-energy laser systems (ELI, HILASE) is in development that requires huge amounts of pump power. Their diode laser pump sources should be low cost ($/W) and operate with the highest power conversion efficiency E. One way to increase both output power and efficiency is to lower the operating temperature. We present latest results of detailed design investigations into 9xx nm, AlGaAs based broad-area devices, specifically targeting low temperature (200K) operation. We show experimentally that decreasing temperature reduces threshold current and increases internal efficiency. However, the series resistance RS increases, limiting the net benefit especially at high powers. To address this limitation, the impact of aluminum content in the diode laser AlGaAs waveguide has been studied using 100 μm wide devices mounted p-up on CuW. Near room temperature, structures with low Al-content in the waveguide have poor optical performance, due to high carrier leakage. However at temperatures around 200K, carrier leakage is shown to be strongly suppressed, eliminating the low-aluminum performance penalty of a higher threshold and lower slope efficiency. Simultaneously RS is strongly decreased for low Al-content structures. Overall, we show that optimized designs should enable single 100 μm broad-area lasers to operate at 200K with E = 72% at 20 W output power, corresponding to about 1.5 kW from a bar with 75% fill-factor.