First down converter multilayers integration in an industrial Si solar cell process

International audienceDown converter SiN x :Yb 3+ /SiN x :Tb 3+ multilayers are deposited by reactive magnetron cosputtering with the objective of optimizing the interaction distance betweenTb 3+ and Yb 3+ ions to favor a better light management in Si solar cells. Those Si‐based multilayers are developed to be compatible with the Si photovoltaic technology. The deposition parameters are optimized to enhance the emission of the Yb 3+ ions in the IR region. The emission efficiency of such multilayer structure is compared with a mixed RE SiN x :Tb 3+ ‐Yb 3+ layer evidencing a gain resulting from a better management of the Tb 3+ and Yb 3+ ions distance. At the end, we integrate the growth of such a multilayer in an industrial Si solar cell process and demonstrate the existence of a frequency conversion effect that is promising for the future increase of the Si solar cell efficiency. KEYWORDS down converter, rare earth ions, Si solar cell efficiency, SiN x , Tb‐Yb 1 | INTRODUCTION The limitation of global average temperature increase to 2°C agreed by the international community at the COP21 Paris's meeting strengthens the need of developing carbon free sustainable energies. To reach this goal, the use of sustainable energy sources, particularly solar energy, has to be optimized while their running cost has to be decreased. In this context, continuous improvements have been done on silicon solar cell that is actually the most used nowadays solar power generation. Thus, a typical conversion efficiency of about 20% is industrially validated and more recently a value as high as over 26% 1 has been achieved in lab. Thus, increasing its efficiency while keeping a low cost process is one of the goals of the silicon‐photovoltaic (Si‐PV) industry to continuously decrease the cost of the power generation and thus increase its competitiveness. The limited efficiency of Si‐PV comes principally from thermal-ization of photogenerated minority carriers. 2 Hence, the energy excess of these photogenerated excitons with respect to the Si solar cell (Si‐SC) bandgap energy is released into the matrix. As a result, besides a limited energy conversion, such a process may increase the cell temperature and therefore reduce the efficiency of the cell. For example, an increase of 1°C above 25°C leads to a decrease of the SC efficiency by around 0.65% 3-5 and results in its faster aging. Several ways to improve the SC efficiency 6 are thus investigated such as tandem cells, 7,8 surface textur-ing, 9,10 antireflective layer, 11-13 or frequency conversion layer. 2,14-20 In that respect, down conversion (DC) answers the thermalization issue by converting high energy photons to a greater number of lower energy pho-tons with energies close to the Si‐SC gap. Many systems using a couple of rare earth (RE) ions, such as Pr 3+ ‐Yb 3+ , 21-23 Tb 3+ ‐Yb 3+ , 24-27 and Ce 3+ ‐ Yb 3+ , 28,29 have been studied for the DC approach. The major drawbacks of those different developed systems are the use of a non–Si‐compatible process due to the nature of the host matrix and/or the low absorption cross section of the RE ions that limits their excitability in the solar spectrum range. 15,30 To overcome this problem, a Si‐PV compatible host matrix containing sensitizers has been developed in our group taking into account that such a host matrix should have good antireflective properties to be used as antireflection coating (ARC). 3