Passivated emitter rear side contact solar cells

Öztürk, Zeynep Nilüfer
The purpose of this research is to identify the production processes and working principles of passivated emitter and rear contact (PERC) solar cells and produce working PERC samples. PERC solar cells are extremely promising among next generation industrialized solar cells due to their high efficiencies and low costs. Backside of a PERC cell is coated with dielectric layer with micro holes that increases the recombination time thus increases the overall efficiency. Moreover, the top surface of the cell is textured with pyramids and bottom surface of the cell is polished which provides better light confinement as well as increases quantum efficiencies at longer wavelengths. Thus, PERC cells have crucial importance for the solar cell industry. PERC solar cell’s working principle is very close to standard photovoltaic solar cell working principle. However, PERC cells have some benefits due to its design difference. The most important difference of PERC cell design is local back surface field metal contacts and passivation layer. Backside of a PERC cell is coated with dielectric layer with laser opening holes for back surface metal contacts that decrease the recombination which is directly associated to the overall efficiency. If an electron is generated near the rear side of the conventional solar cell, it is recombined by back vi surface metallization layer and it doesn’t contribute to the overall cell current. However, the dielectric layer of PERC solar cells restrains the electron-aluminium metallization layer attraction. Hence, most of the electrons do reach the depletion region and contribute to the current. Back side metal coverage percentage is the most important parameter for PERC solar cells. With the Transmission Line Method (TLM) measurements, laser parameters were optimized. In this thesis work, EO Technics Super Mark GF pulsed (nanosecond) laser having 1064 nm wavelength, 200 ns pulsed width, 4.5 kW peak power for 30kHz and 30µm focal spot size was used. Laser parameters of having 100% power (27.5 Watt), 5493 mm/s velocity and 25% power (4.75 Watt), 586mm/sec velocity were chosen for the laser ablation. Back side metal coverage percentage is also aimed to be parametrized. Power 100% and velocity 5493 mm/s laser parameter resulted in better results according to other chosen laser parameter. Highest efficiency of 14.1 was obtained with 10% back surface metal coverage percentage parameter. Moreover, PERC cell production results exceeded the results of reference cell produced.