Published on 1 August 2019
Research
Low temperature deposition of Cu(In,Ga)Se2 solar cells on polymer substrates

At the IUPAC 2019 congress in Paris, Daniel Lincot, a researcher at the Photovoltaic Institute of Île-de-France (IPVF) on the Paris-Saclay campus, presented the work carried out in collaboration with the Institute Lavoisier of Versailles (ILV - CNRS/UVSQ) on the deposition of CIGS solar cells on polymers.

Composed of a stack of semiconductor materials, photovoltaic cells are able to absorb light energy (photons) and transform it into electrical energy by creating an electron current and a potential between the positive and negative terminals of the cell. The efficiency of this conversion varies depending on the type of solar cells used.

While crystalline silicon cells are the most common on the market, CIGS cells - a sandwich of thin layers, a few microns thick of copper - are among the most promising photovoltaic technologies. Their development began more than thirty years ago and focused mainly on the deposition of thin-film metals on a glass substrate. The conversion efficiencies obtained with this type of cell are among the highest of the thin-film cells (more than 20 %).

Glass has several advantages: it contains sodium ions which, due to their diffusion effect, mix with the other metals of the photovoltaic cell. This significantly increases the efficiency of the cell. In addition, it resists the high temperatures at which the materials are deposited (about 550 °C).

However, it also has some quite constraining disadvantages for larger scale applications: its weight (7.22 kg/m² for 3 mm thick sheets) and its rigidity, which limit the production of complex and flexible shapes.

In recent years, research efforts have focused on CIGS cells using more flexible and lighter substrates, which are also compatible with printing-type deposition techniques (roll to roll) and offer new application possibilities. Polymers, like polyimides, are one of the pursued tracks: once deposited on this support, the CIGS modules become much lighter (0.06 kg/m²) and deform at will.

The team at the Photovoltaic Institute of Île-de-France Paris-Saclay, worked in collaboration with researchers from the Institute Lavoisier of Versailles (ILV – CNRS/UVSQ) to manufacture new CIGS cells deposited on polymers for photovoltaic applications. They showed that, despite the problems related to the stability of polymers at high temperatures, the deposition of CIGS cells was possible, with efficiencies close to those deposited on glass (about 19 % conversion efficiency).

Today, polymers offer many and varied prospects. As CIGS cells’ optimization has mainly been carried out on glass, a complete revision of their architecture and the metal deposition process is to be expected to make these cells more efficient on the new substrates. The IPVF has joined forces with the ZSW research centre in Stuttgart to initiate the industrial development of the CIGS on polymer sector.

Publication :

M. Balestrieri et al., Improving VocWith Indium and Alkali Fluorides in Cu(In,Ga)Se2Solar Cells Deposited at Low Temperature on Polyimide. IEEE Journal of Photovoltaics, Vol.8, Issue 5, p. 1343 – 1348 (2018).