OPTIMIZATION OF THE KOH TEXTURING PROCESS: BENCHMARKING ON MINORITY CARRIER LIFETIME AND ON N-PERT SOLAR CELL PERFORMANCE

摘要

We report on the progress of wet chemical process development for saw damage removal and silicon surface texturing in n-type passivated emitter with rear totally diffused (n-PERT) solar cells. A KOH based saw damage removal (SDR) and texturing process sequence has been developed which provides both, improved solar cell efficiency and reduction in cost of ownership. On the bases of our best electrical and optical performance we were able to define our optimized KOH based wet process (5 μm SDR + 4.5 μm texturing) in comparison with the reference KOH wet process (0 μm SDR + 9 μm texturing). The optimized texturing wet process provides a reflectance value of less than 10% with a process time of 8 min in 2% KOH solution. The emitter saturation current density (J_(oe)) using the optimized KOH process is extracted from a symmetric lifetime vehicle to be between 30-40 fA/cm~2 for BBr_3 emitter passivated with ALD-Al_2O_3. The Best Known Process (BKP) for SDR + TEX is determined to be, SDR: 5 μm (3.5 min) KOH 20%, 70C and TEX: 4.5 μm (8 min) KOH 2%, 80C. This BKP has been implemented in an n-type PERT with rear emitter and resulted in conversion cell efficiency of 20.6% (average cells) and 20.8% (best cell) as a fist attempt on large area (156×156 mm~2) CZ-Si based cells.