Effect of Additional Heat Treatment in Fabrication Line of n-PERT Bifacial Solar Cell to Improve the Surface Passivation

This work presents optimization of preannealing step at the end of the existing process line of Silicon solar cell device fabrication and compared it with regularly processed n-Passivated Emitter Rear Total (n-PERT) bifacial solar cell. For preannealing purpose, rapid thermal process (RTP) treatment of the device has been performed in the temperature range of 500–900 °C for 20 min duration in the existing process line. The electrical evaluations of the devices are performed via I–V measurements which are depicting variation in respective solar cell output parameters such as open circuit voltage, short circuit current and fill factor with annealing temperature. An optimized heat treatment of RTP at 700 °C suggests appreciable improvement of 0.31% in the device efficiency with improvement in other solar cell parameters such as short circuit current and open circuit voltage by 51.6 mA and 4.8 mV respectively. The measured cell parameters are analysed in detail with the variation of RTP temperature and suggest that additional heat treatment at the end of process line can results into device improvement with the increase of annealing temperature upto 700 °C, via reduction of bulk recombination in the base region without much affecting junction properties in the crystalline Si solar cell. However, high temperature (>700 °C) annealing in the device fabrication line is deteriorating device parameters as well as its efficiency which can be attributed to depletion of hydrogen in passivating layer and degradation of p–n junction properties.