The quest for understanding the operation of polymer solar cells has made it possible for the development of conjugated polymers. This has led to the fabrication of devices with over 10% power conversion efficiency. Longevity stability problems, common for typical polymer solar cells where the cathode is susceptible to water and oxygen degradation, has been curtailed through device structure inversion. Above all, low band gap polymers including PCDTBT have exhibited potential photochemical stability in laboratory and real world operational conditions, posting 7-15 years useful life.
However, production of large-scale polymer solar cells using slot-die coating, inkjet printing, rotary screen-printing, and spray coating methods in the laboratory is less practical considering the high cost of purchase and repeatable operation of the equipment needed. Therefore, most researchers rely on the spin-coating method, which only produces polymer solar cell devices of up to 1cm2, and is unsuitable for large-scale production in view of poor material utilization and issues with scaling up. The use of spin coating also creates discrepancies in industrial and research laboratory results owing to significant non-identical effects in the deposition process on device performance.
To address this, researchers led by Professor S. Ravi P. Silva at the University of Surrey described in their work, the adaptation of an entry level paint applicator to function as a functional slot-die coater. This allowed for the attachment of various coating heads for flexible coating. They described the design of slot-die head and its supporting elements. The slot-die coater was then used to produce polymer solar cell modules with over 3% power conversion efficiency determined over 35cm2 photoactive area. Their work is published in Solar Energy Materials & Solar Cells.
The authors fabricated polymer solar cell devices with a structure of glass -ITO/ZnO/PCDTBT: PC70BM/MoO3/Al. The electron transport layer solution was then slot-die coated onto the glass indium tin-coated glass substrates. The coating process of the PCDTBT: PC70BM layer was carefully undertaken at ambient conditions on top of the zinc oxide layers.
For modules fabrication, the viscosity of the active layer and subsequently the resulting layer thickness was changed by altering the processing temperature and applying three varying donor acceptor concentrations. The authors made two modules from the first two concentrations and one module from the latter.
The modified sheet-to-sheet slot-die coater was used to produce polymer solar cell modules with an active area above 35cm2 and over 3% power conversion efficiency. Optimization of the processing parameters led to homogeneous layers that were characterized by light beam induced current, micro Raman mapping, and micro photoluminescence of the modules. The authors also investigated the behavior of the module at various annealing temperatures as well as its stability during operation, and provide supplementary information on the fabrication of the modified slot die head.
The outcomes of their study provide a route for fabrication of large-scale slot-die coated modules with viable polymer solar cells. This infers that large-scale polymer solar cells can be made with simple coating equipment, therefore, avoiding the high cost of purchase and operation.
The reported work was completed partly in collaboration with European partners through a European Union 7th Framework Programme (FP7) project entitled Smartonics, and partly in collaboration with the United Kingdom’s national measurement institute, The National Physical Laboratory (NPL). The collaboration with NPL has recently been further supported by a grant from the European Union Horizon 2020 Framework Programme to which will create an effective Open Innovation Environment (OIE) for printed electronics, entitled CORNET, combining world-class expert academic, research and industrial entities from 6 countries, as part of a national metrology effort to standardize printable electronics in an organic electronics market which is predicted to grow to $48B in 2019 (IDTechEx).
Prof Silva indicated that: “Consortia such as the FP7 Smartonics programme have contributed much in setting up a framework to establish printable electronics within the European Union. We hope research such as this, and the recently funded CORNET project, will help firmly establish plastic electronics within the UK and Europe, and provide a resource for researchers worldwide.”
Images produced by Dr Dimitar Kutsarov (ATI, University of Surrey)
Dimitar I. Kutsarov, Edward New, Francesco Bausi, Alina Zoladek-Lemanczyk, Fernando, A. Castro, S. Ravi P. Silva. Fabrication of air-stable, large-area, PCDTBT:PC70BM polymer solar cell modules using a custom built slot-die coater. Solar Energy Materials & Solar Cells, volume 161 (2017), pages 388–396.Go To Solar Energy Materials & Solar Cells