IN-SITU HYDROGEN MICROSTRUCTURAL CHARACTERIZATION OF SI HETEROJUNCTION PASSIVATION: ADDRESSING VOC DEGRADATION AND MITIGATION PATHWAYS THE OVERALL OBJECTIVE OF THE PROJECT IS TO DEVELOP AN IN-SITU CHARACTERIZATION METHOD TO DECIPHER AND QUANTIFY HYDROGEN MICROSTRUCTURAL CHANGES OF HYDROGENATED AMORPHOUS SILICON (A-SI:H)-PASSIVATED CRYSTALLINE SI SURFACE DURING EXPOSURE TO LIGHT AND HEAT UNDER DIFFERENT AMBIENT CONDITIONS. RECORD OPEN CIRCUIT VOLTAGE (VOC) IN SI HETEROJUNCTION (SHJ) SOLAR CELL IS ATTRIBUTED TO THE EXCELLENT SURFACE PASSIVATION OFFERED BY THE INTRINSIC A-SI:H LAYERS. HOWEVER, SUCH SHJ CELLS HAVE EXHIBITED A UNIQUE VOC-DRIVEN PERFORMANCE LOSS TRIGGERED BY COMBINATIONS OF LIGHT, TEMPERATURE, AND VOLTAGE. THESE LOSSES ARE INTERNAL TO THE CELL, RELATED TO THE ELECTRONIC AND STRUCTURAL INSTABILITY OF H-RICH A-SI:H LAYERS AND/OR INTERFACES. THIS PROJECT IN ONE BUDGET PERIOD WILL DEVELOP A FOURIER TRANSFORM INFRARED (FTIR) VIBRATIONAL SPECTROSCOPY BASED QUANTITATIVE ANALYSIS OF HYDROGEN CONCENTRATION AND BONDING STRUCTURES IN THE A-SI:H FILM/INTERFACES, MEASURED IN-SITU DURING LIGHT AND TEMPERATURE STRESSES. THESE IN-SITU MEASURED PARAMETERS WILL BE CORRELATED TO THE EX-SITU MEASURED MINORITY CARRIER LIFETIME (¿EFF), IMPLIED VOC (IVOC) AND CELL VOC UNDER SIMILAR ACCELERATED LIFETIME TESTING (ALT) CONDITIONS. THE FINAL GOALS OF THIS PROJECT ARE TO PROVIDE CRITICAL UNDERSTANDING OF VOC-DRIVEN SHJ CELL PERFORMANCE LOSS MECHANISM AND ESTABLISH A CAUSAL RELATION TO GUIDE DEVELOPMENT OF MITIGATION PATHWAYS.