GALLIUM NITRIDE (GAN) PROTECTED TANDEM PHOTOELECTRODES FOR HIGH EFFICIENCY, LOW COST, AND STABLE SOLAR WATER SPLITTING BUDGET PERIOD 1 (M1-M12): WE WILL DEMONSTRATE GAN-PROTECTED PEROVSKITE/SI TANDEM DEVICE AND GAN-PROTECTED GAINP/GAINAS TANDEM PHOTOELECTRODES. A WIDE RANGE OF SYNTHESIS TECHNIQUES, INCLUDING PECVD, MOCVD, SPIN-COATING, SPUTTERING, AND MBE WILL BE UTILIZED. DELIVERABLES: (¿) A REPORT ON THE DESIGN, SYNTHESIS, AND CHARACTERISTICS OF A GAN-PROTECTED PEROVSKITE/SI TANDEM DEVICE AND GAN-PROTECTED GAINP/GAINAS TANDEM PHOTOELECTRODE. (¿) WIRED GAN-PROTECTED PEROVSKITE/SI DOUBLE JUNCTION PHOTOELECTRODE WITH STH OF >10% AND STABILITY OF >100 H; (¿) WIRELESS GAN-PROTECTED PEROVSKITE/SI TANDEM DEVICE WITH PHOTOCURRENT DENSITY OF >12.5 MA/CM2, OCP OF >1.5 V, AND STABILITY OF >100 H; (¿) GAN-PROTECTED GAINP/GAINAS PHOTOELECTRODE WITH STH OF >10 % AND STABILITY OF > 100 H.