Presented at the 37th EU PVSEC, September 2020 - online SILVER- AND INDIUM-FREE SILICON HETEROJUNCTION SOLAR CELL Agata Lachowicz, Gabriel Christmann, Antoine Descoeudres, Sylvain Nicolay, Christophe Ballif CSEM PV-center, Neuchâtel, Switzerland Email: agata.lachowicz@csem.ch ABSTRACT: Currently about 2000 tons of silver are consumed for 100 GW PV production per year and this are 10% of the entire world annual silver supply. Annual production volumes in the terawatt range are postulated by renowned experts already for 2030 and replacement of expensive and rare elements becomes imperative to sustain PV production on such a large scale. Replacement of silver has already been demonstrated and several process options for copper plating on heterojunction cells exist. With our plating sequense, comprising a PVD seed layer and hotmelt inkjet patterning and compatible with chemically resistant thin conductive oxides such as ITO or IWO, high efficiency of 24.7% has been achieved on industrial heterojunction cell precursors and excellent module reliability confirmed in extended ageing tests. This process has been modified for cells having an aluminum zinc oxide layer. In the first cell experiment the efficiency was 0.6% lower than the screen printed reference, because of lower Jsc. This is caused by remaining minor attact on the AZO during processing and optimization of the etch-back solution is ongoing. Keywords: heterojunction, copper plating, aluminum zinc oxide 1 INTRODUCTION Photovoltaics is a fast-growing market. The global cumulated PV installations have increased tenfold, from 40 GW in 2010 to 400 GW in 2017 and the Compound Annual Growth Rate for PV production was 36.8% in the last years [1]. By the end of 2018, the cumulated global PV installations have reached 0.5 TW. The predictions for annual PV production in 2030 differ from 300 GW (IEA), through 700 GW (Breyer “Electricity”) to 1400 GW (“Broad electrification”) [2] [3]. Renowned experts from research, academic and industry envision total PV installations of around 10 TW already by 2030 [4]. To reach this goal the annual growth rate must be at 30 % (calculated with linear growth). The annual production would be 0.6 TW in 2025 and 2.3 TW in 2030, respectively (Figure 1). Even with a smaller annual growth rate of 20% the annual production would still reach 0.9 TW in 2030 (Figure 2). P. Verlinden postulates an annual PV production of 2 TW from 2030 on in order to reach the climate goals [5]. Currently 2000 tons of silver are consumed for solar cell production, assuming 100 mg paste lay-down, 5 Wp per cell and 100 GW annual production. In 2019 already 10% of the entire world silver supply were consumed for the PV sector, for production slightly above 100 GW. [6] Considering only the smaller annual growth scenario (20%) and a strongly reduced silver consumption per cell (50 mg), the silver demand for PV would still amount to at least 10 000 tons in 2030. The silver price has increased by more than 60% in the last months [7] and the replacement of silver becomes necessary for the industry. For PV production on terawatt scale also the replacement of rare elements like indium will be required to avoid material supply issues. With our process sequence for electroplated copper metallization high efficiency has been demonstrated on industrial heterojunction cells and excellent module stability confirmed in extended aging tests. The initial process compatible with ITO has been modified for cells with an aluminum zinc oxide (AZO) electrode and we present the first results of silver- and indium-free heterojunction solar cells. Figure 1: Annual production and cumulated installed PV, calculated with 30% growth rate Figure 2: Annual production and cumulated installed PV, calculated with 20% growth rate 0.00 2.00 4.00 6.00 8.00 10.00 12.002018201920202021202220232024202520262027202820292030 Annual growth rate 20% cumulated installed PV [TW] annual PV production (installations) [TW] 0.00 2.0