Interfaces, Stability and Energy Efficiency: Photochemical Characterisation of Perovskites for Printable Photovoltaics

The clean generation of energy is the most important scientific and technological challenge that faces humankind in the 21st century. Concerns about climate change, energy independence, and depletion of non-renewable reserves, are pushing governments around the world to develop and implement alternative-energy policies and technologies. The development of low-cost, large area, stable photovoltaics is an absolute must to meet humankinds' current, growing, energy need. The current photovoltaic (PV) market, is dominated by crystalline silicon modules (> 85 % of the present PV market). Despite the recent substantial reductions in the manufacturing cost of mainstream silicon PV, there exists clear opportunities for PV technologies that promise either significant higher power energy conversion efficiencies (PCE) or significantly lower processing costs (both in financial and embodied energy terms). Perovskite-based solar cells, offer prospects on both fronts. Perovskite based solar cells are a relatively young technology, first reported in 2009, and have metaphorically opened the door to an exciting, new, highly efficient solid-state photovoltaic technology which could compete with silicon and thin film technologies that require vacuum deposition and/or expensive non-trivial processing. However, stability and lifetime issues must be understood and overcome to progress the field.

Here we aim to look at the photochemistry and stability of printable perovskite photovoltaics with the aim to develop an understanding of materials that are suitable to manufacture at a large scale. This project will focus on developing a detailed understanding of the fundamental processes that govern the photoluminescence (PL) properties of perovskite materials. PL of perovskite thin-films is not as straightforward as initially thought highlighting the sometimes-surprising nature of these materials, here we attempt to unravel the PL data and discuss what this can tell us about these materials. We will study a series of perovskites via fluorescence microscopy (FM) coupled with an optical fibre spectrometer. This allows precise control of the measurement environment (temperature and atmosphere control) and provides information on the bulk and local photoluminescence (PL) and allows us to map the surface of the films and monitor the evolution of photoluminescence with time exposed to various controlled environments. Perovskite materials tend to be sensitive to air/moisture, light and oxygen. Molecular oxygen can be particularly problematic as photo-generated electrons at a semiconductor surface reduce oxygen to radical species and holes which are extremely reactive towards and can result in rapid degradation of devices. We aim to correlate the PL, and the changes in PL with time, with the overall PV device efficiency and stability. This is a rapid and straight forward screening method that does not need the manufacture of a complete device to evaluate and optimise the perovskite properties. This will provide much needed understanding of the stability of these devices and deliver a clear route for the optimisation and improvement of device stability.
Time resolved PL provides vital information on the charge carrier kinetics and extraction (in the presence of charge selective contacts) which is a key indicator of performance. The aim is to achieve a global understanding of the charge carrier lifetime and extraction, achieved through a rigorous control of all the components of the absorber-charge selective contact interface, and an evaluation of the kinetics of charge transfer processes occurring through such interfaces. Charge contacts can then be designed/tailored to maximise conductivity, while minimising back electron transfer and recombination and thus improving device performance.

The primary purpose of the proposed research is to uncover new knowledge of a fundamental nature, contributing to the scientific advancement of perovskite based solar cells. This research will help characterise and evaluate perovskite materials and other components of perovskite solar cells (charge selective layers) with the aim of informing routes for improvement of these devices and identifying best candidates for scale-up. This project could have a drastic effect on developing stable perovskite devices hastening the commercialisation of this technology. Which significant knowledge on this topic the group could cement the place of SU as world-leaders in hybrid perovskite devices.

This project is expected to generate mid- to long term industrial and economic impact for the R+D and energy sectors in the UK. The project will contribute to the understanding and scaling of printable solar cells which will potentially contribute to the future UK energy supply mix. Stable, low cost, high efficiency solar cells could potentially transform the UK economy, accelerating the current uptake of photovoltaics for both domestic and industrial use.

The aims of this proposal are very well aligned to those of the SPECIFIC IKC (SU). The ultimate purpose is to nucleate and accelerate the creation of a new industry in disruptive coating technologies resulting in economic growth. We see this project as an enabler to widen our collaborative network, add our world-class knowledge and facilities to a superlative consortium which can help achieve the goal of SPECIFIC which is to develop a £1bn industry centred on Buildings as Powerstations'.

Positive environmental impact associated with the increased use of photovoltaics in the UK will have significant environmental and societal advantages. It will significantly contribute to a reduction in CO2 emissions, helping to circumvent the impending complication of global warming and climate change.

This project will reinforce collaboration within the he UK (SU-ICL), Europe (SU-Coimbra) and globally (SU-UKZN). The project team individually, and in collaboration, regularly generate IP and publish well-cited papers in high impact journals. The project will generate international quality 4* research publications. The expertise and equipment applications developed during the project will lead to future research projects involving internal and external collaboration.

This project will aim to deliver:
1) Acceleration of the development of perovskite technologies through enhanced understanding of charge transport processes and degradation mechanisms.
2) The dissemination of these results across the scientific and technological communities through:
a) >4 REF 4* papers in high impact international journals, which will be made open access
b) >2 High profile international and national presentations at international and national conferences on subjects ranging from materials chemistry, solar energy manufacturing and technology
c) inform teaching within the CoE SU. The PI currently teaching "Photochemistry of Functional Materials" to doctorates students in the college, the project results will be discussed impacting positively on education and training of the students and increasing the link to, and information on, cutting edge research.

The PI has a significant track record on community engagement through both national and international invited public lectures, the running of hands-on and demonstration workshops, and larger scale outreach events globally. The results of this research project will be disseminated via these opportunities as well as through science media and social media channels. Results, images and breakthroughs will be shared on the SPECIFIC-IKC website and posted on a designated YouTube channel.