Towards Sinter-free Printing of Photovoltaic Cell Interconnects
Lead Research Organisation:
Glyndwr University
Department Name: Science Research Centre
Abstract
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Organisations
Publications
Kartopu G
(2015)
Progression of metalorganic chemical vapour-deposited CdTe thin-film PV devices towards modules
in Progress in Photovoltaics: Research and Applications
| Description | Metallic films/components can be printed at low cost using a solution based ink via the inkjet process. However, these precursor film often requires a post-deposition 'curing' treatment (by a laser or annealing in an oven) to become useful as a conductor. The 'sinter-free inkjet project' aimed at avoiding the post-treatment by developing new metalorganic inks which can be inkjet-printed at relatively modest temperatures, i.e. without causing damage to the printer, and displaying high conductivity without additional treatment. Printing conducting components in a single step and using low cost methods can be attractive for optoelectronic devices, such as solar cells/modules. During the 30 months of this project, mainly metalorganic silver inks were formulated at Liverpool University and by the industrial partner SAFC Hitech. These were then tested across partner labs at Glyndwr University (GU) and The University of Nottingham. Work at GU assessed the inkjet printing behaviour of these inks on glass and cadmium telluride thin film solar cell surfaces. To obtain compact and sufficiently thick silver films with good conductivity, the substrates were heated to above 150 oC and several overlayers printed by multi-passing the injector. A further and surprising beneficial effect was that the new inks were 'non-selective' on the substrate type, as opposed to the conventional inks and could therefore be easily printed on all relevant solar device surfaces, providing a huge benefit for PV module design. In contrast, commercial (colloidal) inks required special substrate treatment (such as plasma cleaning, acid etch, etc.) for most substrate materials as well as sintering at 150 Celcius for at least one hour to attain good coverage and conductivity. Thus the new sinter-free process considerably reducing the thermal cycle and the processing time. Solar cell performances were found to be comparable when using the newly developed and conventional silver inks. As the final step towards sinter-free inkjet-printing of PV sub-cell interconnects (for PV modules), electrical resistance of sinter-free silver films deposited over 'P2 scribes' to assess the vital connection between the front and back contact of successive cells. This was assessed using novel test structures designed to mimic a portion of a thin film module. Good ohmic contacts, were obtained for all the test samples with the electrical resistance reducing proportionally with increasing film thickness, demonstrating excellent control of the electrical conductivity. In the future, it would be desirable to work on the ink formulation, to further reduce the required substrate temperature (towards 100 Celcius and below) and increase the metal load/concentration, as well as fully demonstrate large-scale optoelectronic devices, e.g. solar modules, with high performance in order for the sinter-free inkjet process to become more attractive for industrial uptake. |
| Exploitation Route | This project has opened up a new approach to printing conducting tracks onto electronic devices. The conformality of the coating over different surfaces could have benefit to a range of printed electronic devices from displays through to sensors. A further reduction in the printing temperature would expand this range of applications and, in the case of solar PV devices, enable novel device architectures for more integrated PV devices. More research will be required to fully unlock this enormous potential. |
| Sectors | Aerospace, Defence and Marine,Chemicals,Digital/Communication/Information Technologies (including Software),Electronics,Energy,Environment,Manufacturing, including Industrial Biotechology |
| URL | http://cser.org.uk/research/ |
| Description | During the course of this project, the main supplier of the organometallic inks, SAFC Hitech, withdrew from manufacturing at the Bromborough facility where a considerable amount of research had taken place over the years into organometallic precursors for compound semiconductor synthesis. Although this was disappointing the strength of the relationship with the Liverpool and Glyndwr partners has enabled key staff from SAFC Hitech to set-up a new organometallic supply business based in Saltney, Flintshire. This new business, Pegasus Chemicals, is now in a position to supply a range of organometallic precursors to both industry and academic researchers. This will also provide a route for commercialisation of the sinter-free precursors once they have become suitably developed. The knowledge gained in using inkjet printing for novel thin film PV module fabrication has directly benefited research funded under a European Regional Development Fund project (SPARC II), funded through the Welsh European funding Office (WEFO). An exciting development in PV technology is the powering of semi-autonomous sensors from building monitoring to soil monitoring in agriculture. One of the SPARC II partners at Bangor University required a small robust PV module for powering these sensors in a demonstrator project. The lead researcher on the "Sinter-free Printing of PV Interconnects" project, Dr Giray Kartopu, was able to supply a mini-module that enabled a successful demonstration and the results have now been incorporated into a paper that has been accepted for a lecture presentation at the 2020 IEEE World Forum on Internet of Things, to be held in New Orleans, Louisiana, USA April 5-9, 2020. The paper is titled, "Development of a Wireless Sensor Node for Building Information Management Systems". Other developments of the mini-module PV design are being investigated on SPARC II for solar PV modules on ultra-thin glass for space applications. The processes learned on the EPSRC project have been crucial to these further developments. |
| Sector | Aerospace, Defence and Marine,Chemicals,Digital/Communication/Information Technologies (including Software),Electronics,Energy,Manufacturing, including Industrial Biotechology |
| Impact Types | Economic |
| Title | Ink Jet printer (PixPro LP50) |
| Description | The PixPro LP50 was commissioned and modified on the Sinter Free research project to produce highly conducting metal contacts for thin film photovoltaic (PV) cells. The information learnt on the research project is now being applied to innovative designs of monolithic modules and in particular thin film PV modules on ultra-thin glass (UTG). The use of UTG is extremely challenging when fabricating monolithic modules that could be the basis for practical ultra-light-weight PV arrays. The information gained on the Sinter-free inkjet project has enabled a new avenue of research to minimize strain that will be included in a new research proposal to EPSRC on fundamental aspects of strain in functional devices on UTG. |
| Type Of Material | Improvements to research infrastructure |
| Year Produced | 2017 |
| Provided To Others? | Yes |
| Impact | Too early to assess impact but ongoing discussions with UTG glass manufacturers and research collaborators at University of Surrey on the strain proposal. |
| URL | http://www.cser.org.uk |