PERMASOL Perovskite Materials for Efficient Solar Cells

Projektverlauf

The projects progresses along two main parallel tracks.  The first track is the ab-initio, band structure simulations of the new perovskite absorbers, based on strontium, bismuth, germanium, copper, antimony and other inorganic cations with a stable +2 oxidation state.  These perovksites have not only a 3D structure, defined by the formula ABX3, but can also adopt lower dimensionalities (2D or quasi 0D).  Further they can be hybrid (with A being an organc cation) or all-inorganic (with A being an inorganic cation like Cs+).  In parallel with the ab-initio investigations, the experimental synthesis/deposition of the perovskite materials took place, using solution-based and vacuum-based techniques.  The absorbers were characterized in terms of processability, layer morphology, crystal structural and optical properties (like absorbance and bandgap).  A direct comparison between theory and experiment was thus possible, allowing the adjustment of the experiments in order to test and, in many cases verify, the theoretical predictions.  SImultaneously, other material components (such as planar and 3D scaffold electrodes) have been developed in order to enable the fabrication of complete solar cells using the most promising perovskite absorbers.  Time resolved characterization methods were employed to gather information about the carrier dynamics in materials and devices.      

Meilensteine

1. Participation in international conferences/peer-reviewed publications
2. Identification of at least one new perovskite with appropriate semiconductor properties for PV application
3. Successful synthesis of at least one perovskite with: energy bap 1-2 eV, high absorption coefficient, carrier diffusion length more than 100 nm and stability better than 500 h in inert gas
4. Determination of the exciton and free carrier contributions in the new perovskites
5. Solar cells based on the new perovskites with power conversion efficiency of >7% and stability of at least 500 h under controlled atmosphere and/or encapsulated

Ergebnisse

The result highlights of the project up to now, can be summarized as follows:

• A large number of Pb-free perovskites, based on bismuth (Bi), antimony (Sb), copper (Cu), germanium (Ge) and tin (Sn) were ab-initio calculated and several compounds identified with appropriate bandgap for solar cell applications.
• The experimental realization of solar cells based on Bi, Sb, Ge, and Sn (using both solution- and vacuum-based techniques) yielded significant power conversion efficiencies, which in certain cases surpass the state-of-the-art in the literature. 
• Processing routes were developed that significantly enhance the efficiency and stability of Sn-perovskites, through purification, appropriate compound composition and passivation approaches. A maximum efficiency of 5.6% was obtained, stable over several days in inert atmosphere.   
• High structural stability of 2D perovskites in ambient conditions was demonstrated, as well as modification of their structural anisotropy through the use of a 3D electrodes, in order to enable their use in devices of perpendicular architecture, such as solar cells.

Peer-reviewed publications:

[1]          S.F. Hoefler, G. Trimmel, T. Rath, Progress on lead-free metal halide perovskites for photovoltaic applications: a review, Monatshefte Für Chem. – Chem. Mon. 148 (2017) 795–826. doi:10.1007/s00706-017-1933-9.

[2]          I. Kopacic, B. Friesenbichler, S.F. Hoefler, B. Kunert, H. Plank, T. Rath, G. Trimmel, Enhanced Performance of Germanium Halide Perovskite Solar Cells through Compositional Engineering, ACS Appl. Energy Mater. (2018). doi:10.1021/acsaem.8b00007.

[3]          D. Ebner, M. Bauch, T. Dimopoulos, High performance and low cost transparent electrodes based on ultrathin Cu layer, Opt. Express. 25 (2017) A240. doi:10.1364/OE.25.00A240.

[4]          A. Koliogiorgos, S. Baskoutas, I. Galanakis, Electronic and gap properties of lead-free perfect and mixed hybrid halide perovskites: An ab-initio study, Comput. Mater. Sci. 138 (2017) 92–98. doi:10.1016/j.commatsci.2017.06.026.

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