>200 CM2 TYPE-3 PEC WATER SPLITTING PROTOTYPE USING BANDGAP-TUNABLE PEROVSKITE TANDEM AND MOLECULAR-SCALE DESIGNER COATINGS THIS RESEARCH ADDRESSES A TECHNOLOGY BARRIER TOWARDS ACHIEVING A FULLY-INTEGRATED LARGE-SCALE, HIGHLY EFFICIENT, AND STABLE PHOTOELECTROCHEMICAL (PEC) TYPE-3 WATER-SPLITTING DEVICE THAT COLLECTS SOLAR H2 AT >200 CM2 LIGHT CAPTURE AREA. WE PROPOSE TO DEVELOP ADVANCED MANUFACTURING PROCESSES TO INTEGRATE MULTIPLE LARGE-AREA TANDEM PEROVSKITE CELLS INTO A TYPE-3 PEC WATER SPLITTING PROTOTYPE SYSTEM, SIMULTANEOUSLY ACHIEVING HIGH EFFICIENCY (SOLAR-TO-H2 EFFICIENCY OF 20%), HIGH PURITY (>99.999VOL%) H2 PRODUCTION, LONG-TERM STABILITY (>1,000 HOURS OR >2-WEEK DIURNAL OPERATION), AND 0.12 GRAM H2 PER HOUR THROUGHPUT. THE FIRST OBJECTIVE IS TO DEVELOP ULTRA-NARROW BAND GAP PB-SN PEROVSKITE SYSTEM (I.E., EG < 1.1 EV) VIA DOPING AND ALLOYING AND TO OPTIMIZE THE THIN-FILM PROCESSING FOR ACHIEVING HIGH OPTOELECTRONIC PROPERTIES. THE GOAL IS TO FINE-TUNE THE SPECTRUM SPLITTING AND CURRENT MATCHING OF THE ASSEMBLED PEROVSKITE TANDEM CELLS, PROVIDING SUFFICIENT PHOTOVOLTAGE FOR THE WATER-SPLITTING CATALYSIS ARRANGED LOCALLY TO THE TANDEM PHOTOABSORBERS WITHOUT COMPROMISING PHOTOCURRENTS. THE SECOND OBJECTIVE IS TO ESTABLISH A STREAMLINED COATING, CATALYST, AND DEVICE INTEGRATION MANUFACTURING PROCEDURE FOR COST-EFFECTIVE H2 COLLECTION OVER A LARGE AREA. WE WILL TILE (3-INCH)2 TANDEM PEROVSKITES INTO A 2×2 ARRANGEMENT FOR A FULLY INTEGRATED TYPE-3 SOLAR WATER-SPLITTING PEC DEVICE. WE WILL COLLABORATE WITH EMN NODE EXPERTS AT LBNL, LLNL, AND NREL TO DEMONSTRATE ON-SUN OPERATION WITH HIGH EFFICIENCY AND DIURNAL STABILITY, AND TO UNDERSTAND MECHANISMS OF PERFORMANCE DEGRADATION WHICH INFORM THE PROCESS IMPROVEMENT FOR PEROVSKITE ABSORBERS, COATINGS, AND CATALYST INTEGRATION.