Periodic Reporting for period 3 - p-TYPE (Transparent p-type semiconductors for efficient solar energy capture, conversion and storage.)
Periodo di rendicontazione: 2020-01-01 al 2021-06-30
n-Type transparent conducting oxides are present in many devices but their p-type counterparts are not largely commercialized as they exhibit much lower conductivities. The core part of the project focuses on making libraries of mixed metal oxides and selecting those which are promising p-type semiconductors. Our high-throughput synthesis and screening system will enable us to accelerate the discovery and optimisation processes. Promising materials are assembled in tandem DSCs and tested. Our objectives are: A) Improve the efficiency of p-type dye sensitized solar cells and water-splitting cells by incorporating new p-type semiconductors which, for the first time, combine good transparency and high conductivity. B) Drive innovative engineering for the fabrication of high-efficiency low-cost tandem devices incorporating new photocathodes as a means of converting the majority of solar radiation striking the Earth. C) Underpin our research with state-of-the-art techniques for solar cell characterization to connect the fundamental research carried out at the molecular level and the events that take place in the device as a whole.
We have optimised a formulation which allows us to print arrays of compounds on conductive glass, for screening according to their transparency, conductivity and sensitization by a dye. We have also developed and validated a method to screen the arrays new materials with combinations of dyes. From our simple diagnostic tests, we are able to identify the materials fulfilling most or all of the optoelectronic criteria for efficient tandem cells. We characterise and classify interesting materials according to their chemical and electronic structure, both at the surface and the bulk, their morphology and optoelectronic properties. Specifically, we have shown that XPS can be used to probe the energy alignment of the electronic orbitals of the dye with the states in the semiconductor, which determines the performance of the device. We then use these results to understand how the structure and properties of the materials affects the dynamics of charge-separation at the dye-semiconductor interface, under operational conditions. The results of new materials, initially based on NixMyOz and CuxMyOz, are compared to our benchmark materials, NiO and CuCrO2. As well as dyes, we have tested inorganic absorbers (quantum dots), which have tuneable band-gaps, large absorption coefficients, can transfer charge rapidly to a second semiconductor, but are faster to synthesise than dyes.
We have presented results at several major national and international conferences. We have also carried out public engagement activities to showcase our research at the Science Museum London and the Great North Museum (Hancock) Newcastle. We are also working on technology transfer and hosted an intern from an international company, who we trained to make flexible solar cells.
To quickly screen the materials, we have taken a technique used widely in medicinal chemistry and pioneered its application towards materials discovery and solar cell device assembly and characterisation for the first time. This provides a rapid and non-destructive method to scan combinations of materials/processing techniques/module configurations to accelerate the development of thin-film photovoltaic (PV) technology.
We have also shown how XPS using hard and soft X-rays from a synchrotron source can be used to probe the energy alignment of dyes with the valence band of semiconductors. Previously this was used for looking at the alignment of the energy of the states in the dye with those in n-type semiconductors, which was a simpler process. This new approach is providing us with more information about the interface between the molecules and the material which cannot be achieved with such accuracy by any other technique.
Our research in tandem quantum-dot sensitized solar cells has advanced the efficiency beyond what has been achieved with dyes and has demonstrated the potential for flexible devices. It has also provided a route to address the mass-transport limitations in our solar cells. We still have some concerns over the sustainability of some of the materials used, and future work will address this. There is much optimisation still left to do, but we anticipate that we can exceed 15% efficiency during the period of the grant.