Numerical simulation of the impact of design parameters on the performance of back-contact back-junction solar cell

Abstract

This work presents a study based on electro-optical numerical simulations of the impact of geometrical and doping parameters on main figures of merit of crystalline silicon back-contact back-junction solar cells. State-of-the-art physical models in combination with two-dimensional simulations performed by a TCAD tool have been adopted to carry out an extensive and detailed analysis of the influence of many fabrication parameters on performance. The studied design parameters are the doping level in front surface field (FSF), back surface field (BSF) and emitter, and the main geometrical parameters. A doping level value that allows the maximization of the efficiency for the three regions can be clearly identified. In particular, for BSF and emitter, an efficiency degradation is observed for relatively lower doping values and is ascribed to the higher contact recombination while for higher doping values the Auger recombination plays a significant role in reducing the ultimate efficiency. In FSF region the recombination due to defects at the front interface is the main limiting mechanisms for efficiency. On the basis of our analysis, a marked sensitivity of the efficiency to the gap and pitch size is caused by the series resistance increase. The efficiency exhibits a maximum value for an emitter coverage fraction (R) of 85 %. However, in the case of lower emitter coverage, Auger, Shockley–Read–Hall (SRH): in bulk and at interfaces are detrimental for the cell conversion efficiency

High‐Efficiency Interdigitated Back Contact Silicon Solar Cells with Front Floating Emitter

“…For the back side of the FFE‐IBC solar cells, Figure a shows that the Eff is monotonically decreasing with the increase in gap width, keeping constant the pitch of 1200 μm and 1/2 width ratio of BSF to emitter in the simulation. We know that the variation of resistivity trade‐off in the rear region from longer gap could degrade the value of FF of the solar cells . In addition, due to the lack of effective field effect passivation (i.e., preventing the high density carrier from reaching the noncollection interface), undiffused gap would usually result in heavily carrier recombination .…”

“…The J 0 increases from 9.5 to 22.0 nA cm −2 versus junction densities increase from 5 to 40 cm −1 for the S gap of 50 cm s −1 , indicating that the pitch cannot be too small. Many previous theoretical studies have shown that the cell efficiency increases with the decrease in pitch because the p–n junction on the surface is not considered …”

“…Although the IBC solar cells can yield more photogenerated carriers as a result of the elimination for optical shading loss, the carriers have various losses before being collected by the electrodes, such as Shockley–Read–Hall (SRH) loss, Auger recombination, interface recombination, and non‐ohm‐contact recombination loss. The continuous reduction of carrier recombination losses has always been a subject for scientific research institutions and enterprises .…”

Simulation Results: Optimization of Contact Ratio for Interdigitated Back-Contact Solar Cells

“…The current transfer length is defined as a distance over which the current transfers from a metal contact to a diffused region. There are various articles in the literature [19][20][21][22], which simulated the IBC solar cells at different dimensions of emitter and BSF but they did not optimize the dimensions of contact with respect to emitter and BSF, and contact size was chosen irrespective of the dimensions of emitter and BSF. However, there are very few articles in the literature, which simulated the impact of contact size on contact resistance [23], sheet resistance [24], saturation current density [25], and leakage current density [26].…”

“…For modeling, we used a software tool called Quokka, which is able to simulate silicon solar cell devices in 1D/2D/3D [27]. The back surface of IBC solar cell looks like ZEBRA crossing which is symmetric around one emitter and BSF [28] that is why the simulation of unit cell, which consists of half emitter and BSF, resembles the behavior of a complete IBC structure [15,16,20,24]. In this work, we are simulating the unit cell of IBC structure in three dimension.…”