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Sustainable Mixed-ion Layered Perovskite Solar Cells

Periodic Reporting for period 1 - MPerS (Sustainable Mixed-ion Layered Perovskite Solar Cells)

Reporting period: 2015-04-01 to 2017-03-31

The state-of-the-art perovskite-based solar cells reported during the start of the project used halide perovskites, a toxic material. The main objective of the project was to develop Sustainable Mixed-ion Perovskite Solar Cells. Towards that end, we aimed to developed non-toxic Bi and Pd based materials and demonstrate potential applications in optoelectronic devices. We also aimed to find a mechanism for the rapid crystallization of perovskite materials which is central to the electronic properties of these materials. During the device fabrication stage, we found the need to develop ways to dope organic semiconductors which play important role in device performance.
Work Package 1 (WP1)
In WP1 we planned to develop new materials for solar cell and other optoelectronic applications. The materials that were developed are (i) Hexyldiammonium bismuth iodide (HDABiI5) (ii) Butyl diammonium bismuth iodide (BDABiI5) (iii) Ethyl diammonium bismuth iodide (EDABiI5) and (iv) Cesium Hexabromopalladate(IV), Cs2PdBr6. These materials were synthesized and characterized by single crystal X-ray diffraction, Uv_Vis and other methods.
Work package 2
In work package 2, we planned to develop devices based on materials developed in WP1. The devices based on the materials show potential applications in optoelectronic devices and e found to be stable under ambient condition. However, the device efficiencies are low and the reasons for the low performance were (a) incompatibility of commonly used hole transporting materials due to the mismatched energetics at the interfaces. (b) the presence of trap states that reduces the device performance
This prompted us to (i) understand the crystallization process that controls the electronic properties of these materials (ii) look for new hole transporting materials and ways to dope it.
Work package 3
In work package 3 we aimed to understand the mechanism for the crystallization of perovskite materials which is central to the thin film formation in these materials. From Infra-red spectroscopy, Static light scattering measurements and several other types of spectroscopic investigation we found that rapid crystallization in perovskites is due to the dissolution of colloids which can happen by a change in acidity of the solution, and due to a change in the solvent strength. The dissolved colloids increase the concentration of free ions in solution leading to supersaturation and the onset of crystallization.
Work package 4
In WP 4, we aimed to develop a new method to dope organic hole transporting material which is crucial for device fabrication. The method that we developed uses inexpensive chemicals and is compatible with both solution and vapor phase method of thin film preparation. With this doping method, we can now prepare perovskite solar cell with >20% power conversion efficiency
We developed new non-toxic materials and showed that they have potential applications in optoelectronic devices.
The fundamental study on crystallization of the perovskite materials shows the way to prepare these materials and single crystals with reproducible electronic properties.
The new method of doping organic semiconductors now opens up ways for inexpensive and flexible ways to make organic based optoelectronic devices
Mechanism for Perovskite Crystal formation