WWithin the first reporting period, the main focus was set on the training activities. Besides these activities, each doctoral candidate has started with their individual research projects.
Work package 1: Stability of devices
The objective of WP 1 is an in-depth analysis of the ageing parameters on the lifetime of complete OPV devices including high-throughput screening, accelerated ageing tests and detailed device characterization. This allow a fast identification of suitable materials combinations and determination of the major degradation triggers. Materials and architectures are clustered according to their degradation trends, in order to select the most stable materials.
Activities were directed towards (accelerated) stability tests under controlled indoor as well as outdoor conditions with devices based on a set of high performing OPV materials, e.g. PM6/Y6, L8-BO/D18, and others. The initial test series already gave a first insight into the differences in stability of the materials, together with additional trends regarding the influence of film thickness and process parameters on the stability. These data are currently analyzed and will be used as input for further stability tests and input for the other scientific work packages.
Work package 2: Stability of materials, morphology and interfaces
WP2 focuses on the intrinsic stability of organic semiconductors and degradation pathways of materials, interfaces and absorber layer morphology. These are investigated by systematic studies at the nanoscale in order to understand degradation caused by the interactions of all components in a solar cell and to unveil hidden degradation triggers. This is combined with theoretical modelling and chemical space sampling to identify stable and weak structural components in OPV absorber materials.
Structural changes: Here, selected materials systems are studied under controlled ageing conditions, i.e. under dark conditions as well as under illumination in inert and ambient atmosphere. Changes in the absorption and emission spectrum give information on the bleaching of the conjugated system. These investigations are supported with resonant Raman spectroscopy showing structural changes of the chemical backbone.
Morphological changes: The nanophase morphology of the donor and acceptor in the active layer is of crucial importance for the efficiency. Thus, the thermal stability of the morphology was investigated using wide and small angle X-ray scattering methods on samples after different stages of thermal annealing.
Work package 3: Strategies toward next generation OPV
WP 3 is based on the results of the other WPs and will implement the findings in order to get highly efficient and stable solar cells. Additionally, the effect of antioxidants (e.g. additives known to inhibit degradation of organic (polymeric) materials) on the stability will be elaborated.
In this context, first test series with antioxidants have been carried out and yielded promising results.
Work package 4: Simulation, big-data analysis & machine learning
WP4 will implement big data mining, machine learning and simulations to analyze data generated via high throughput experiments in order to identify stable materials and to develop predictive models for next generation OPV devices.
Thus, work focused on the implementation of data management and processing guidelines, in order to make the project data usable. Furthermore, first machine learning models as well as simulation tools have been elaborated.
