NOVA-Cell - Non Vacuum deposition & metallisation of CIGS solar cells

NOVA-Cell will exploit the potential of chalcogenide-based thin film photovoltaics technology for the development and scale up of new processes for the production of low cost efficient solar cells compatible with mass production. Current state of the art thin film PV technology is dominated by cadmium-tellurim (CdTe), amorphous silica (a-Si) and copper-indium-gallium-selenide (CIGS) solar cells. The application and commercialisation of CdTe is limited due to the presence of toxic cadmium and the scarcity of high-cost tellurium. Amorphous silicon thin film is the most mature of thin film
technologies, suggesting that efficiency gains will be merely incremental. Commercially available CIGS cells are manufactured using physical vapor deposition (PVD) and screen printing of Ag pastes. PVD exhibits limited uniformity of deposition across large areas, requires expensive vacuum based capital equipment and exhibits process drift as the PVD targets are eroded. Conventional screen printing techniques limit the resolution of electrode printing, and silver pastes are typically 2-3 x the price of nano-Cu and subject to considerable price volatility due to the commodity trading of silver. NOVA-Cell's main objective is to explore and evaluate the technical feasibility of novel methods for the manufacture of CIGS thin film solar cells. The methods that will be addressed include the deposition of CIGS solar cells via a novel nonvacuum
technology (CASVD) with high-efficiency at low cost, and the deposition of nano copper metallic electrode structures using high-resolution printing technology (ESJET) to reduce cell cost/Watt by 10.6%, and to reduce shading losses (representing a 0.6% cell efficiency gain).

Our approach will be:
(1) to optimise the CIGS absorber material by controlling ratio of its components to obtain the desired chemical composition;
(2) to optimise the CIGS structural properties through control of the deposition rate and temperature;
(3) to conduct a robust design of experiments to optimise the intermediate selenisation step for increased absorbance of the solar cell, including the selenium pressure, the temperature and the selenisation time; (4) to conduct transmission line model deposition measurements to modify the contact and sheet resistance of the ESJET deposited Cu metalisation;
(5) to deposit Cu electrode structures onto CIGS;
(6) to conduct initial efficiency and accelerated lifetime measurements.

The work programme is detailed in Appendix B and is summarised below: WP1: Management [M1-M12, PVI], WP2:
Exploitation and Dissemination [M1-M12, PVI], WP3 CSAVD CIGS deposition [M2-M11, UCL], WP4: ESJET Cu metallisation study [M2-M11, PVI] WP5: Cell Testing and accelerated lifetime measurements [M6-M12, UCL].

The NOVA-Cell project will contribute to a significant breakthrough in the competitiveness of thin film PV technologies developed at small area lab scale by the optimisation of materials and also the transference towards industrial scale-up and
exploitation. The main objective of the NOVA-cell business project is to reduce the cost/Watt of CIGS solar cells by combining the application of non-vacuum CSAVD (to increase the CIGS deposition rate), with the use of novel high resolution ESJET printing of cost effective copper electrode structures.

Innovate UK funding will act as a catalyst, bringing the key knowledge holders together and enabling the consortium to effectively bridge the commercial 'Valley of Death' and bring the IP developed by the partners to the market as quickly as possible whilst reducing the financial risks. Innovate UK funding will allow us to exploit our intellectual capital relating to CSAVD deposition (developed by Choy, now at UCL) and high resolution ESJET printing (developed by PVI). Without this funding there is a real possibility that the commercial benefits resulting from the exploitation would be realised over much longer timescales and that non-UK technologies are developed first.

The technical feasibility of the project will demonstrate the viability of the proposed technology going forward and, further investment will be needed to bring the technology to the market. This will result in further spend within the partnership, and
within the UK in both technology areas (CSAVD and ESJET). This additional R&D spend extends far beyond the initial funds contained within this grant. Once the overall viability has been proven, the technology development and associated scale-up programmes should generate several million of additional R&D within the UK. Furthermore, several potential project ideas have already been generated by working on the proposal together and this is likely to lead to related research topics supported by both partners.

Need for a UK approach:
Achievement of the objectives requires for the development of a collaborative action at industry and university bilateral cooperative programs. The use of a UK approach allows to take profit of the strong background and competences available
at both groups, and exploiting their complementarities for the consolidation of a competitive PV industry.

The technical feasibility of the project will demonstrate the viability of the proposed technology going forward, and significantly, further investment will be needed to bring the technology to the market. This will result in further spend within the partnership and the UK in both technology areas (CSAVD and ESJET). This additional R&D spend extends far beyond the initial funds contained within this grant. Once the overall viability has been proven, the technology development and associated scale-up programmes should generate several million of additional R&D within the UK. Achievement of the objectives requires for the development of a collaborative action at industry and university bilateral cooperative programs. The use of a UK approach allows to take profit of the strong background and competences available at both groups, and exploiting their complementarities for the consolidation of a competitive PV industry.