DEMONSTRATION OF A ROBUST, COMPACT PHOTOELECTROCHEMICAL (PEC) HYDROGEN GENERATOR WE WILL UTILIZE HIGH-EFFICIENCY, DUAL-JUNCTION ORGANO-HALIDE PEROVSKITE/SI PV ARCHITECTURES TO DEMONSTRATE HIGHLY INTEGRATED, COMPACT, EFFICIENT, AND ROBUST PHOTOELECTROCHEMICAL H2 GENERATORS. UTILIZING SIZE-MATCHED GEOMETRIC AREAS FOR LIGHT ABSORBERS, ELECTROCATALYSTS, AND MEMBRANES, IN THE FIRST BUDGET PERIOD WE WILL DEMONSTRATE PEC WATER SPLITTING DEVICES OF =0.25 CM2 WITH STH EFFICIENCY =15% FOR 0.5 H UNDER AM1.5 ILLUMINATION. IN THE SECOND BUDGET PERIOD WE WILL IMPROVE THE PERFORMANCE AND DURABILITY OF THESE SIZE-MATCHED =0.25 CM2 PEC WATER-SPLITTING DEVICES WITH STH EFFICIENCY =15% FOR 100 H UNDER AM1.5 ILLUMINATION. IN THE THIRD BUDGET PERIOD WE WILL IMPROVE THE PERFORMANCE AND DURABILITY OF THESE SIZE-MATCHED =0.25 CM2 PEC WATER-SPLITTING DEVICES TO ACHIEVE INITIAL STH EFFICIENCY =25% WITH DURABLE STH EFFICIENCY OVER 15% FOR 1000 H UNDER AM1.5. ADDITIONALLY, IN THE THIRD BUDGET PERIOD WE WILL DEMONSTRATE 0.1 G/H H2 GENERATION FOR TWO WEEKS UNDER DIURNAL CYCLING, REQUIRING SIGNIFICANT INCREASE IN THE DEVICE AREA TO OVER 100 CM2.