After 18 month of collaborative works, the main results achieved in the ROTROT project are detailed below:
New materials have been developed.
Active materials: Among the materials proposed by Merck, the first promising polymer has been identified and was tested by FAU, DTU and CEA. PCEs above 7% have already been achieved in single cell. Merck has invested large amount of work in order to propose a low band gap polymer whose absorbance spectra is complementary to the first selected polymer. While waiting for further optimisations, the consortium has extended its field of study to commercially available LBG materials in order to fulfil the ROTROT objectives.
Hole transporting layer: A strong interaction with HERAEUS and the labs in charge of the realisation of OPV cells has been established in the project. Various formulations compatible with the R2R process have been proposed. At this time, formulations have already been identified depending on the interface concerned.
Adhesives: The best candidates have been selected among the products developed by DELO on the basis of peeling tests. Currently, characterizations of these adhesives combined with commercial high barrier films are in progress as determined in the requirements of ROTROT.
Top electrode: The development of a challenging Aluminium ink is in progress at VTT. Currently, works are oriented toward formulation tests in the view of a deposition on top of inverted solar cells.
Based on simulations performed at FAU, we should be able to create an OPV tandem cell with a PCE above 11% with the active material already developed by Merck in ROTROT. The low band gap polymer used in this simulation presents a good complement to the Merck materials, but it cannot be disclosed for the moment. Further tandem cells realized at the lab scale by FAU and CEA have achieved PCEs above 6%. The best tandem cells have achieved 6.6%. First tandem cells and modules have been realised by FAU on a sheet-to-sheet coater. Cells and modules with a PCE above 4% were realised.The R2R process flow is now defined. DTU is now able to coat all the layers that compose the tandem cell, including the new polymer developed by Merck (see following pictures).An important work has also been realised to demonstrate the capability of simultaneously coating two layers used in tandem solar cells by use of a double slot-die coating head. The process has proven to be extremely delicate but DTU has successfully performed the coating of two distinct layers by use of a double slot-die coating head.
These first results are very encouraging for the promotion of OPV technology for energy production. Moreover, we demonstrate the feasibility of R2R processing for the fabrication of tandem OPV modules that will have a major impact on reducing the costs of this technology.