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

Lead Research Organisation: Swansea University
Department Name: School of Engineering

Abstract

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.

Planned Impact

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 collaboratio 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.
 
Title Award "Research as Art" 
Description "I see a green future This is a photograph of a thin perovskite layer magnified 10 times using an optical microscope. Perovskite materials are good candidates for inexpensive solar panels although their lifetime still requires improvement. Initially this sample did not present any remarkable features, however, following several weeks in storage striking details began to emerge. This image most likely arose from the presence of impurities in the perovskite layer or from degradation of the material over time. The resulting structure resembles an eye with a vivid green crystalline iris surrounding an ebony pupil" by: Emmanuel V. Péan - College of Engineering, SPECIFIC In collaboration with: Catherine S. De Castro (SPECIFIC), James McGettrick (SPECIFIC), Tamara McFarlane (SPECIFIC) 
Type Of Art Image 
Year Produced 2018 
Impact Higher visibility of the group's research 
URL https://www.swansea.ac.uk/research-as-art/2018---winners-and-runners-up/
 
Title Back Cover for Issue 1 of Chem. Commun. 
Description Showcasing research from the group of Dr Matthew Lloyd Davies, Applied Photochemistry Group (@Photochem_SU), SPECIFIC IKC, Materials Research Department, Swansea University, Wales, UK. The work was carried out in collaboration with Dr Peter Holliman, Swansea University. Improving the light harvesting and colour range of methylammonium lead tri-bromide (MAPbBr3) perovskite solar cells through co-sensitisation with organic dyes Through the introduction of organic dyes into mesoporous MAPbBr3 perovskite devices, we have highlighted the availability of 'space' within the device, which, when occupied by a dye can contribute to colourful and higher performing devices. 
Type Of Art Artwork 
Year Produced 2019 
Impact Higher publication and group visibility 
URL https://pubs.rsc.org/en/content/articlepdf/2019/cc/c9cc90005e?page=search
 
Description The photoluminescence (PL) properties of perovskite thin-films can provide great insight into the ability of the perovskite in a photovoltaic device. Intense PL, in the absence of contact layers, is indicative of a low trap-density and uniform and potentially well-performing device while low PL indicates a high degree of trap states and poor performance in a photovoltaic device. The problem, however, is that the photoluminescence behaviour of perovskite thin-films is unstable and extremely sensitive to the environment, even more sensitive that first realised. To this end, we have made a number of key findings regarding the photoluminescence properties:
- We have a paper currently in preparation that will advise the field on the environmental factors that affect the photoluminescence in both manufacture of thin-films and in the measurement. This will hopefully lead to more reliable data in the literature and help the field advance more rapidly.

- We have also recently published that perovskite thin-films can also be degrading at the same time as exhibiting a phenomenon known as photo-brightening (this is increasing PL with time under illumination associated with the passivation of defect states). This is thought of in the field as a positive behaviour as passivation of these states, and increasing PL, is associated with a better photovoltaic device, however the knowledge that this photo-brightening can mask the degradation is concerning and needs to be addressed.

- With an accurate protocol in place we can now rapidly screen the PL of perovskite thin-films that have been processed via different conditions to indicate the relative stability of these materials.

- We have investigated the stability of carbon-contact perovskite solar cells to reactive oxygen species. These devices utilise ammonium valeric acid iodide as an additive and have shown excellent stability and our research will shed light on the origin of this stability. This work is in preparation for publication.

- We have demonstrated improved performance of methylammonium lead tri-bromide perovskite devices through the use of organic dyes. We prove that there is charge injection from both the dyes and perovskite through external quantum efficiency measurements and we also believe there is an improvement in the perovskite uniformity through interaction with the dye solvent. We believe that these results highlight that there is 'space' within mesoporous perovskite devices to control and improve the device, whether this be colour tuning, improved stability, improved light harvesting efficiency or indeed all three.
Exploitation Route For the academic community, an accurate a reliable method for measuring the PL properties of perovskite thin-films, as well as identifying the factors affecting the PL properties is likely to help guide the field to more accurate, meaningful and reliable data which will accelerate our understanding of perovskite materials. We are currently developing similar protocol for the measuring of time-resolved PL of perovskite thin films.
Our developments on the co-sensitisation of perovskites with organic dyes, we believe, opens an interesting door for perovskite technology where larger band-gap perovskites can be used in combination with dyes to achieve colour control of devices. This is also a potential route for improving the performance and/or stability of devices. This new approach we believe will gain traction in the academic field but hopefully hasten developments in approaches to the manufacture of perovskite devices. The future emergence of perovskite technology onto the market will potentially have an enormous effect on job creation and generation of innovative, green energy technology that will aid our push to a low-carbon economy.
Sectors Energy,Environment,Manufacturing, including Industrial Biotechology

 
Description It is still at an early stage to demonstrate significant economic and societal impact due to the award of this grant. However, it has enhanced the reputation of the Applied Photochemistry Group in Swansea helping in securing funding through an EPSRC Fellowship for Dr Davies which has created 2 post-doctoral positions at SU as well as PhD position. This award was also supported through the provision of a PhD student. A mix of departmental and collaborator funding has allowed the group to purchase an Edinburgh Inst. time-resolved single photon counting set-up and a new fluorometer. This is, in part, due to the developed reputation of the group in carrying out accurate photochemical analysis. The named researcher on this award, Dr Catherine De Castro, has developed her reputation under this award demonstrated by being promoted as well as becoming a member of the Royal Society of Chemistry and elected member of the Royal Society of Chemistry Photophysics and Photochemistry Group. The findings from this award have also been included in a number of public outreach events showcasing the importance of the next generation of photovoltaics in helping to solve some of the problems facing humankind.
First Year Of Impact 2018
Sector Creative Economy,Energy,Environment
Impact Types Economic

 
Description Characterisation and developed understanding of printable photovoltaic materials was directly taught to EngD students in the module "Photochemistry of Functional Materials"
Geographic Reach Local/Municipal/Regional 
Policy Influence Type Influenced training of practitioners or researchers
 
Description ACceleration of Circular Economy for Printable Photovoltaics Through Eco-Design (ACCEPTED)
Amount £547,407 (GBP)
Funding ID EP/S001336/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 06/2018 
End 06/2021
 
Description International Conference on Solar Power at IIT Delhi 2019 (ICPHPV - 19) workshop - Early Career Researcher funding
Amount £1,340 (GBP)
Organisation London South Bank University 
Sector Academic/University
Country United Kingdom
Start 02/2019 
End 02/2019
 
Description Scientific Meetings Grant - The Royal Society of Chemistry
Amount £1,000 (GBP)
Organisation Royal Society of Chemistry 
Sector Learned Society
Country United Kingdom
Start 09/2018 
End 09/2018
 
Description Swansea University Capital Equipment for ECRs
Amount £100,000 (GBP)
Funding ID EP/S017925/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 11/2018 
End 05/2020
 
Description Blog from the Royal Society of Chemistry Photochemistry Group Early Career Members Meeting 2018 on the SPECIFIC webpage 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact The idea behind writing a blog regarding the conference organized by one of the member of the SPECIFIC team was to reach other audiences, especially within the industry where the Royal Society of Chemistry Photophysics and Photochemistry group would like to be more involved with.
Year(s) Of Engagement Activity 2018
URL http://specific.eu.com/rsc-photochemistry-group-early-career-members-meeting/
 
Description Chief organizer of the Royal Society of Chemistry Photochemistry Group Early Career Members Meeting 2018 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact The Royal Society of Chemistry Photochemistry Group Early Career Members Meeting has been set to bring together students, researchers, academics and industrialists from across the United Kingdom and Ireland to showcase the recent developments in the areas of photochemistry and photophysics of molecular, supramolecular structures and materials with applications across a wide range of fields from photovoltaics to healthcare. This meeting was held at Trinity College Dublin in 2011, Queen's University Belfast in 2013, Newcastle University in 2015, University of Birmingham in 2017 and Swansea University in 2018.
From this year's edition, several collaborations were born, new members joined the group and the visibility of the group increased.
Year(s) Of Engagement Activity 2011,2013,2015,2017,2018
URL http://www.rsc.org/events/detail/33561/rsc-photochemistry-group-early-career-members-meeting
 
Description Conference report from the Royal Society of Chemistry Photochemistry Group Early Career Members Meeting 2018 for RSC Photophysics and Photochemistry Group 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact This conference report has not been made available yet.
Year(s) Of Engagement Activity 2019
 
Description Contribution for the blog on the International Conference on Solar Power at IIT Delhi 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact Contribution on the International Conference on Solar Power at IIT Delhi blog
Year(s) Of Engagement Activity 2019
URL http://www.sunrisenetwork.org/news/international-conference-on-solar-power-at-iit-delhi/
 
Description Selected for Participation International Conference on Solar Power at IIT Delhi workshop 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact The workshop included topics such as: "The art of Scientific Publication", securing funding, etc.
Year(s) Of Engagement Activity 2019
 
Description Webpage for advertising the RSC Photochemistry Group Early Career Members Meeting 2018 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Media (as a channel to the public)
Results and Impact A webpage was set within the university website to advertise the event, this was in both English and Welsh.
Year(s) Of Engagement Activity 2018
URL https://www.swansea.ac.uk/engineering/research/photochemistry-group-meeting/