Controlled Crystallization of the Methylammonium Halide Layer in Thin-Film Perovskite Solar Cells

• Applicant: Dr. Christian Weinberger
• Subject Area: Solid State and Surface Chemistry, Material Synthesis ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: from 2016 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 322532324

To boost the performance of perovskite solar cells, especially the growth of the crystalline perovskite phase needs to be improved, as stated above. This is the objective of this project proposal.1. Scaffold designTo date most of the porous scaffold layers that are used for the fabrication of structured films for photovoltaic energy conversion are based on interconnected, granular particles, which limits the control of the porosity of the generated film. The size of the inter-particular voids (pores) in particle-based films is generally quite small and exhibits a broad distribution. To increase the pore size it is necessary to use larger particles, which at the same time decreases the efficiency. Therefore, ordered mesoporous scaffolds (synthesized by the sol-gel method or by nanocasting, details are stated in the work plan) bear the advantage of larger pores at constant wall thickness. A larger pore size will allow for larger (yet still confined) perovskite crystals with fewer grain boundaries where charge recombination can occur. Therefore the project aims at a pore size between 5 nm and 100 nm. The advantage of such a nanoporous scaffold lies in the narrow distribution of pore sizes, which is advantageous to particle-based films. 2. Influence of the crystallization and crystallite size of the perovskite-containing layer on the performance of the deviceThe deposition of a uniform perovskite-containing layer is one of the key challenges in the preparation of efficient and reproducible PSCs. A nanoporous scaffold layer (as stated above) facilitates better control of the crystallization process.3. Charge transport and recombination in perovskite solar cellsClarifying the charge transport and recombination in perovskite solar cells is of paramount importance in developing efficient devices, i.e. by tuning the perovskite crystal size (see Objective 2.1) or by developing and implementing novel charge-selective contacts. This adjustment of the energy levels (band structure) of the structured films increases the performance of the perovskite solar cells, aiming to minimize the recombination at the contacts and to extract charges. Therefore, it is necessary to clarify the drift length and charge carrier mobility within the device. These parameters can be determined by charge carrier extraction by linearly increasing voltage (CELIV measurements.

• DFG Programme: Research Fellowships
• International Connection: Finland
• Hosts: Dr. Jan-Henrik Smått; Professor Dr. Ronald Österbacka