THE OBJECTIVES OF THIS PROJECT ARE: (1) FABRICATE MONOLITHIC BIFACIAL HALIDE PEROVSKITE-CADMIUM SELENIDE TELLURIDE (CST) TANDEM SOLAR CELLS WITH EQUIVALENT POWER CONVERSION EFFICIENCIES (PCES) OVER 22% MEASURED UNDER THE STANDARD BIFACIAL ILLUMINATION CONDITIONS; (2) DEMONSTRATE TANDEM DEVICES WITH T90 LIFETIMES (RETAINING 90% OF THEIR INITIAL PERFORMANCE) OF MORE THAN 1,000 HOURS UNDER CONTINUOUS BIFACIAL ILLUMINATION; (3) ADVANCE THE CURRENT UNDERSTANDING OF THE UNIQUE WORKING MECHANISM OF BIFACIAL THIN-FILM TANDEM SOLAR CELLS; (4) ENGAGE WITH STAKEHOLDERS TO EVALUATE THE POTENTIAL FUTURE MANUFACTURING OF THIS NEW TECHNOLOGY. FIRST, WE WILL FABRICATE BIFACIAL SINGLE-JUNCTION PEROVSKITE AND CST CELLS SEPARATELY AND IDENTIFY THE OPTIMAL BANDGAP COMBINATIONS FOR BIFACIAL PEROVSKITE-CST TANDEM CELLS. SECOND, WE WILL DEVELOP MONOLITHIC BIFACIAL PEROVSKITE-CST TANDEM CELL INTEGRATION TECHNIQUES AND OPTIMIZE THE ABSORBER LAYERS, THEIR INTERFACES, AND THE INTERCONNECTING LAYERS TO IMPROVE THE EFFICIENCY AND STABILITY OF THE BIFACIAL TANDEM DEVICES. FURTHERMORE, WE WILL EVALUATE THE RELIABILITY OF THE BIFACIAL TANDEM CELLS AND DEVELOP STRATEGIES TO ENSURE THEIR STABLE OPERATION. LASTLY, WE WILL ENGAGE INDUSTRIAL AND ACADEMIC STAKEHOLDERS AND CONDUCT A TECHNOECONOMIC ANALYSIS TO EVALUATE THE FEASIBILITY OF THIS BIFACIAL TANDEM TECHNOLOGY.