2, Sandia National Laboratories, Albuquerque, New Mexico, United States
We investigate the thermal stability of InGaN solar cells under thermal stress at elevated temperatures from 400°C to 500°C. High Resolution X-Ray Diffraction (HRXRD) analysis reveals that material quality of InGaN/GaN did not degrade after thermal stress. The external quantum efficiency (EQE) characteristics of solar cells were well-maintained at all temperatures, which demonstrates thermally robust nature of InGaN materials. Analysis of current density–voltage (J–V) curves indicates that the degradation of conversion efficiency of the solar cell is mainly caused by the decrease in open-circuit voltage (Voc), while short-circuit current (Jsc) and fill factor (FF) remain almost constant. The decrease of Voc after thermal stress is attributed to the compromised metal contacts. Transmission line method (TLM) results further confirmed that p-type contacts became Schottky-like after thermal stress. The Arrhenius model was employed to estimate the failure lifetime of InGaN solar cells under different temperatures. These results suggest that while InGaN solar cells have high thermal stability, the degradation in metal contact could be the major limiting factor for these devices under high temperature operation.