(Invited) Electrodeposition for Large Scale Photovoltaic Deployment : A Prospective Trial
Authors: Lincot Daniel , Chassaing Elisabeth , Duchatelet Aurelien , Grand Pierre Philippe 
Published: February 2020

Photovoltaics is entering a new age. With more than 300 GW of cumulative capacity by the end of 2016, while it was almost zero ten years ago, which represents about 1.5% of the world electricity production, photovoltaics is becoming a key component in the energy transition. The situation is even more evident when considering the contribution of photovoltaics country by country, reaching about 8% in Germany, Italy, Greece. it is also emerging very rapidly in USA, China, India, Chile for instance. It is anticipated that the level of 500 GW will be reached by 2020 and the symbolic one of one TW in the next decade. The reason is that photovoltaics is becoming economically competitive with the traditional energy sector with negociated prices as low as 3 cents per kWh in some regions. However to go futher in this direction will need an disruptive evolution of all the production chain to lower the costs, increase the efficiency and increase the throughput. Up to now the photovoltaic industrial sector is mostly based on wafer based silicon technology and on vaccuum based thin film solar cells of cadmium telluride or copper indium gallium diselenide (CIGS). Electrodeposition is almost absent in this industrial lanscape, excepted for the emerging copper plating technology for the contact in silicon solar cells, and the other experiences for implementing the electrodeposition in thin film technologies failed. Our vision is that in the new context there will be a unique opportunity to demonstrate that electrodeposition can be implemented as a disruptive technology for larger scale PV depoyment.

We will recall the results obtained for the electrodeposition of CIGS solar cells from the laboratory to the industrial pilot line in Nexcis ( a spin off of our laboratory). Using a two stage approach from the electrodeposition of metallic precursors followed by thermal selenization, a record cell efficiency of 17.3 % was reached, and modules with full size (120 x60 cm2) at 14% efficiency in 2015, which was equivalent to the state of the art for CIGS modules prepared by vaccuum methods. Unfortunately for economic reasons, as many CIGS companies at that time, the company was stopped in 2015. However the unique features of the CIGS electrodeposition technology for large area and high throughput and robustness was successfully demonstrated. This research line has been maintained in our laboratory and is presently reactivated taking the lessons of the Nexcis experience. We will discuss a new process for the electrodeposition of CIGS absorbers, via an intermediate step consisting in single bath electrodeposition of mixed oxide hydroxyde copper indium gallium layers followed by thermal hydrogen reduction to form the metallic layer before selenization. The deposition of transparent conductive oxide layers by photoelectrodeposition has been successfully developped too and may become a new standard to replace more costly sputtering methods [2-4. We will also present applications and devices which specifically take benefit from a unique advantage electrodeposition approach, that is localized deposition on structured substrates. Two examples will be given: one for the electrodeposition for photovoltaic semitransparent windows and the second one for the deposition of microcells and microlines for a new concept of PV modules working under concentration. In that case we will also discuss of the mechanisms of electrodeposition of multicomponent CIGS films in conditions of microelectrode array configurations, and the challenges for upscaling.

We will conclude with some prospective views at longer term as for instance for using electrodeposition in the next generation of PV modules with higher efficiencies (>30%) based on tandem devives, in that case electrodeposition of thin film solar cells could be combined with classical silicon bottom cells.

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