Industrial PERC+ solar cell efficiency projection towards 24%

article
2020
authors
Dullweber, T. and Stöhr, M. and Kruse, C. and Haase, F. and Beier, B. and Jäger, P. and Mertens, V. and Peibst, R. and Brendel, R.
journal
Photovoltaics International

abstract

Monofacial passivated emitter and rear cells (PERC) and bifacial PERC+ solar cells have become the mainstream solar cell technologies in today’s PV industry, with conversion efficiencies of around 22.5% being demonstrated in mass production. Ten years ago, the PV market was dominated by monofacial Al-BSF solar cells, with conversion efficiencies around 18%, while the first industrial prototype PERC cells reached 19% efficiency. This paper reviews the key technology improvements which have enabled a continuous 0.5% b /year increase in efficiency of industrial PERC and PERC+ cells. Most importantly, all saturation current density contributions of PERC cells have been steadily reduced, thereby enabling a noteworthy increase in Voc from 620mV in 2010 to 685mV today. A breakdown of all J0 contributions of current industrial PERC+ cells is presented on the basis of actual measurements at ISFH, and a projection is provided of the improvements in J0 of industrial PERC+ cells which are feasible within the next two years, supported by published research results. These J0 values are used as input parameters for Quokka simulations of PERC+ solar cells, according to which an increase in efficiency towards 23.8% within the next two years is predicted. A main limitation of these future PERC+ cells will be the specific saturation current density J0 Ag = 1,400fA/cm2 of the screenprinted Ag front contact. When carrier-selective poly-Si on oxide (POLO) fingers are used below the screen-printed Ag contacts, the Quokka simulations predict a further efficiency increase to 24.1% for these so-called PERC+POLO solar cells. The simulation results are in good agreement with published efficiencies of the first R&D-type PERC+POLO cells. However, the challenge remains of how to cost-effectively manufacture local poly-Si fingers. The local plasma-enhanced chemical vapour deposition (PECVD) of poly-Si fingers through a shadow mask is proposed as a possible manufacturing solution.