BarcelonaTech Researchers send jolts of innovation into solar cell technology with ALD

Researchers at Polytechnic University of Catalonia sends jolts of innovation into solar cell technology with ALD

Researchers at Polytechnic University of Catalonia sends jolts of innovation into solar cell technology with ALD

University of Catalonia, Electronic Engineering Department

Universitat Politècnica de Catalunya / BarcelonaTech, Building for Electronic Engineering Department

The Micro and Nanotechnologies Research Group (MNT) at the Polytechnic University of Catalonia have a long-standing history of executing ALD in various technologies, with such publications dating as far back as 2013. Within the span of 4 months, two separate studies have just been published by the group on the feasibility of ALD techniques in solar cell production. Dr. Eloi Ros Costals and Dr. Gerard Masmitjà, established experts in electronic engineering, are the leading coauthors on both papers. 

Costals et al shows the way with ALD on how to boost industrial production of solar cells that have transition metal oxide films

Eloi Ros Costals et al has published a paper in Material Advances that reveals how atomic layer deposition (ALD) can be a more easily scalable alternative for developing solar cell selective contacts made of transition metal oxides (TMOs). The research team demonstrates that ALD is effective in depositing a thin film of vanadium oxide, in which the film acts as a hole-selective contact for the frontal transparent contact of n-type crystalline silicone solar cells. Also revealed by their work is the surface passivation properties of the V₂O₅ film, eliminating the need to separately add a passivating layer typically done by Plasma-enhanced chemical vapor deposition (PECVD).

 
   
Using ALD to make TMO films as selective contacts

Selective contacts are a standard functional feature of solar cells where either electrons or holes are collected upon junction with the crystalline silicon layer.  Currently the standard application technique requires  thermal evaporation, which does not fare well in large scale production. Costals and the MNT team aims to replace the standard technique for depositing TMOs onto silicon, to move toward a more attainable and scalable means of producing solar cells with TMO selective contacts.  

     
The results from their research are promising, as their experimental c-Si solar cell made with ALD-deposited vanadium oxide HTL contacts measured at an average of 18.6% efficiency.  As the V₂O₅-based contact contributes to only about 37% of the total series resistance, the researchers write that work can be done to improve resistance measurements in the other components of this solar device – such as the ITO layer and the silver grid.

Masmitjà at UPC shedding light on how ALD techniques can make IBC solar cells

With the groundwork for ALD application of V₂O₅ films established in their prior study, the MNT group was quick to emerge with a second publication in the Solar Energy Materials and Solar Cells Journal.  

In this research, Masmitjà and team set out to apply a V₂O₅ film as a hole selective contact in a different type of solar cell: n-type c-Si solar cells with an interdigitated back-contacted (IBC) architecture. Their goal was to pave the way for low thermal-budget, low cost, and highly scalable methods in IBC solar cell fabrication by employing ALD. They also aim to circumvent the use of a-Si:H interlayers by use of ALD technique, eliminating the need for hazardous procedures to develop a-Si:H interlayers while still meeting relevant standards of efficiency.     

The result of their work is the first known IBC solar cell with a structure fully made by ALD, yielding a measured solar efficiency of 18.6% with potential to reach 21.1%. The following pieces were constructed by ALD:     

• V₂O₅ film acting as the hole transport layer       
• TiO₂-based stack acting as the electron-sensitive contact (with Al₂O₃ stacked via ALD)       
• Al₂O₃ film acting as the surface passivation layer in non-contacted regions    

As IBC solar cells offer comparatively improved solar absorption and overall efficiency compared to other current solar cell systems, the MNT group aimed to meet the industry at the point at which scalable production of IBC solar cells are being prevented.  Their implementation of ALD technique may be the key unlocking the path to increasing industry applications of IBC solar cells.