Comparison of Different Rear Contacting Approaches for Industrial PERC Solar Cells on mc-Si Wafer

Abstract

Ecole Polytechnique Federale de Lausanne, 1015 Lausanne – Switzerland ABSTRACT: The technology transfer of highly efficient solar cell concepts (i.e. passivated emitter and rear cell PERC) to industry can help reduce their production cost. This work appraises three different industrial approaches for the technology transfer and a conventional processing with a fair comparison. A significant improvement compared to conventional processing was obtained. All advanced approaches lead to an increase in open circuit voltage and short circuit current. This testifies to the benefits of improved passivation of the rear surface and a bettered light trapping. The optimal processing window for the advanced approaches has lower fill factor than the conventional processing. However, the reduction does not result in lower conversion potential. Finally, the PERC type devices deliver a significant increase of more than 0.4 % absolute in conversion efficiency. The structure which proved best was based on laser fired contacts (LFC). A maximum efficiency of 17.0 % has been achieved on 1.8 Ωcm multi-crystalline silicon. Keywords: PERC, inkjet, laser ablation, multi-crystalline silicon. 1. INTRODUCTION In recent published studies [1], a roadmap towards lower production cost was delineated. It features higher production volumes, higher efficiency silicon solar cells with respect to conventional present technology and lower silicon wafer thickness. This work addresses the two latter challenges by proposing optimized process sequences. Furthermore, these sequences are applied to multi-crystalline silicon (mc-Si), which has a lower intrinsic production cost. The increased ratio of surface to volume draws the attention to surface passivation. The work will detail different options to locally contact the base through the passivation on the back surface. The adaption of conventional screen printing techniques highlights the value of the here investigated technology transfers for the industry. Different local contacting techniques were already presented in [2-4]. However, differences, especially in back surface passivation and starting material, hindered their direct comparison. This work aims to test each advantageous for the light trapping [7] and for an enhanced passivation potential [8].