Quantitative local efficiency loss analysis on cast-mono PERC solar cells using the DLIT ‘local I-V’ method

Dark lock-in thermography (DLIT) combined with the ’local I-V’ method is applied to derive spatial-resolved efficiency losses and potentials for cast-mono PERC solar cells during wafer and cell developing phase. For the DLIT image evaluation method, four DLIT images at -1 V, 0.510 V, 0.555 V and 0.615 V as well as a lumped series resistance image from photoluminescence are measured at a cast-mono PERC solar cell exemplarily. From these five images, the ‘local I-V’ method derives locally I-V curves which allow spatial-resolved efficiency, open-circuit voltage and fill factor images. Main losses visible in the efficiency image could be separated into: small angle grain boundaries of the cast-mono wafer, stripe like contamination due to belt transportation within a wet bench, increased contact resistance at rear contacts at two sides of the cell and highly recombination active rear pad areas. The overall efficiency drop due to these local losses is calculated to about 0.8%_abs.