Long-Range Charge and Energy Transfer at Heterojunctions for Photovoltaics Beyond the Shockley-Queisser Limit

Lead Research Organisation: University of Cambridge
Department Name: Physics

Abstract

The development of high-efficiency low-cost renewable energy sources is one of the most pressing research challenges today. Two promising technologies in this area are photovoltaics (PV) and Solar Fuel generation systems. PV work by absorbing sunlight to generate electrical charges that are then collected in an external circuit. Solar Fuel systems work by absorbing sunlight and then using the charges produced to drive redox chemistry to produce chemical fuels from readily available starting materials, for example splitting water to produce H2, which is a powerful fuel.

But the cost to efficiency ratio of both these technologies is too high currently. In order to drive the price of these technologies down to match fossil fuels, fundamental breakthroughs are required in the way these systems harness solar energy. This project seeks to tackle this challenge by building on recent insights into quantum mechanical processes in organic semiconductors to improve the efficiency both of current and future PV systems as well as put in place new design ruled for high-efficiency solar fuel generation systems.

At the heart of many kinds of PV and Solar Fuel systems are interfaces between organic and inorganic semiconductors. The role of these interfaces, known as heterojunctions, is to separate opposite charges, hole and electrons, from each other and prevent their recombination. We will use the latest breakthroughs in ultrafast laser spectroscopy to study these interfaces and develop novel structure that efficiently separate charges.

The biggest energy loss in PV is a process known as thermalization. This refers to the fact that the absorption of a high-energy photon generates one electron-hole pair just as the absorption of a low-energy photon does. The extra energy of high-energy photons above the bandgap is lost as heat. This problem affects all commercially deployed PV today and has long been considered a fundamental loss. Indeed it leads to what is known as the Shockley-Queisser limit on efficiency, which is 33% for an idea PV of bandgap 1.1eV. Here we will use a unique quantum mechanical process in organic semiconductors called Singlet Exciton Fission, to overcome this loss. Singlet Fission allows two electron-hole pairs to be generated in certain organic materials when a photon is absorbed. We will design new ways by which these electron-hole pairs can be harvested at the organic/inorganic interface, leading to improved efficiencies. The methods and structures we will develop using this process would be compatible both with current and future PV technologies, allowing them to over come the Shockley-Queisser limit on efficiency. This could dramatically improve the efficiency of PV and help bring about their wide scale deployment.

Planned Impact

The development of new high-efficiency photovoltaics (PV) and photocatalysis technologies is crucial to long term environmental sustainability, allowing for decarbonisation of the global economy. This will in future enable renewable energy to meet the price point of conventional fossil fuels, which is required for large-scale adoption of these technologies.

Key to this effort is the development of new technologies that can surpass existing paradigms of performance. This project seeks to establish such technologies by harnessing the quantum mechanical properties of organic semiconductors to create a new generation of organic/inorganic heterojunctions. The results are likely to find broad application in the areas of PV and photocatalysis, as well as opening new avenues in spintronics and quantum technologies.

The UK has no manufacturing base in PV today. On the other hand, the UK is a leading player in the organic and printed electronics area. This project could allow this strength to be capitalised on, via the production of solution processable thin organic down-converters that would be compatible with both current and future PV technologies, allowing the UK to gain a share of the PV market in the near to medium term. This technology could allow all single junction PV cells to better harness solar energy and approach the Shockley-Queisser limit. Moreover, the technology would be compatible with materials and manufacturing processes for current PV technologies, which could enable easy adoption. Thus the project is likely to be of wide interest to both the PV and printed electronics industries. Technologies resulting from the project will be taken forward via collaboration with industrial partners and engagement with the wider PV industry through forums such as the EPSRC Supergen SuperSolar Hub.

Publications

10 25 50
 
Description Research output generated in this project has lead to a collaboration with an industrial partner, Eight19 (a Cambridge UK based company) who develop flexible roll to roll processed solar cells. This collaboration is looking to develop a organic thin film 'Photon-Multiplier' technology to improve the efficiency of silicon solar cells. This collaborative research is also supported by an grant from Innovate UK and EPSRC (EP/N509929/1,SiFi - Singlet Fission photon multiplier film to increase photovoltaic efficiency). Based on our research and collaboration with Eigth19, they have been able to raise significant investment to further the commercialisation of this technology. We are also woking with Total SA, one the largest energy companies in the world and the second largest manufacturer of Si PV modues in the world, to further the commercialisation of our Photon Multiplier technology.
Sector Energy
Impact Types Economic

 
Description Energy Catalyst
Amount £58,664 (GBP)
Organisation Innovate UK 
Sector Public
Country United Kingdom
Start 11/2015 
End 09/2016
 
Description FIG - FLUX INCREASING GLASS TO ENHANCE PHOTOVOLTAIC EFFICIENCY
Amount £600,000 (GBP)
Funding ID 103757 
Organisation Innovate UK 
Sector Public
Country United Kingdom
Start 11/2017 
End 10/2019
 
Description PINSTRIPE - PHOTON INCREASE BY SPLITTING TO REALISE IMPROVED PHOTOVOLTAIC EFFICIENCY
Amount £232,000 (GBP)
Funding ID 132952 
Organisation Innovate UK 
Sector Public
Country United Kingdom
Start 11/2017 
End 10/2018
 
Description PhD Studentship - 2 - Hope Bretscher, Raj Pandy
Amount £200,000 (GBP)
Organisation Winton Programme for the Physics of Sustainability 
Sector Academic/University
Country United Kingdom
Start 10/2016 
End 03/2020
 
Description PhD Studentship - PV CDT
Amount £80,000 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 10/2017 
End 09/2021
 
Description Photon Management for Solar Energy Harvesting with Hybrid Excitonics - SolarX
Amount € 1,500,000 (EUR)
Funding ID 758826 
Organisation European Research Council (ERC) 
Sector Public
Country European Union (EU)
Start 04/2018 
End 03/2023
 
Description Rational design of manufacturing processes for next generation optoelectronically active nanocomposite films and coatings
Amount £1,000,000 (GBP)
Funding ID EP/P027741/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 04/2017 
End 03/2020
 
Description SiFi - SInglet FIssion photon multiplier film to increase photovoltaic efficiency
Amount £809,851 (GBP)
Funding ID EP/M024873/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 07/2015 
End 06/2018
 
Title Ultrafast Vibrionic Spectroscopy 
Description Tool to study ultrafast dynamics electron-phonon coupling and its effects on electronic processes 
Type Of Material Improvements to research infrastructure 
Year Produced 2015 
Provided To Others? Yes  
Impact Nature Physics 11, 352-357 (2015) doi:10.1038/nphys3241 
 
Title Research Data Supporting Order Enables Efficient Electron-hole Separation at an Organic Heterojunction with a Small Energy Loss 
Description Pump Push Probe Transient Absorption Images for PIPCP and PIPCP:PCBM Films. Images were acquired as described in the associated manuscript. Images were acquired as a function of Pump Probe delay time at a variety of Pump Push delays, Push energies, Push fluences, and Pump fluences. Also included are the Pump Probe and Push Probe images that are acquired simultaneously 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
 
Title Research data supporting "Vibronically coherent ultrafast triplet-pair formation and subsequent thermally activated dissociation control efficient endothermic singlet fission" 
Description This data corresponds to the data presented in the Journal Article, " Vibronically coherent ultrafast triplet-pair formation and subsequent thermally activated dissociation control efficient endothermic singlet fission" conducted in the Cavendish between years 2013-2016 by Stern and co-workers. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
 
Description Eight19 
Organisation Eight19
Country United Kingdom 
Sector Private 
PI Contribution Expertise in singlet fission and photon-multiplier technology, photophysics, devices physics, synthesis of inorganic semiconductor nanocrystals
Collaborator Contribution Expertise in thin film processing and coating technology, commercialisation, manufacturing and product development.
Impact 3 Innovate UK projects, 1 completed successfully (SiFi - SInglet FIssion photon multiplier film to increase photovoltaic efficiency) and 2 ongoing (FIG - Flux Increasing Glass to enhance photovoltaic efficiency) & (PINSTRIPE: Photon Increase by Splitting to Realise Improved Photovoltaic Efficiency"). My team's work and collaboration with Eight19 has helped them raise significant investment to pursue the commercialisation of the Singlet Fission Photon Multiplier technology developed in my lab as part of this grant. Eight19 have a team of 3 scientists embedded in my group. 5+ patent applications filed.
Start Year 2015
 
Description NSG Pilkington 
Organisation Pilkington Glass
Country United Kingdom 
Sector Private 
PI Contribution We have an ongoing Innovate UK grant with two industrial partners Eight19 and NSG Pilkington , PINSTRIPE - PHOTON INCREASE BY SPLITTING TO REALISE IMPROVED PHOTOVOLTAIC EFFICIENCY. This is a 2 year grant helping to commercialise out singlet fission technology to improve conventional Si solar cells. We bring detailed photophysics, optoelectronics and device fabrication knowledge to the project.
Collaborator Contribution NSG Pilkington bring knowledge of manufacture of solar grade glass, encapsulants, glass processing, deposition of films on glass, environmental leaching tests
Impact Ongoing 2 year (11/2017-10/2019) Innovate UK project, PINSTRIPE - PHOTON INCREASE BY SPLITTING TO REALISE IMPROVED PHOTOVOLTAIC EFFICIENCY
Start Year 2017
 
Description Oxford 
Organisation University of Oxford
Department Department of Chemistry
Country United Kingdom 
Sector Academic/University 
PI Contribution Organic semiconductor materials
Collaborator Contribution Ultrafast spectroscopy
Impact Nature Physics 11, 352-357 (2015) doi:10.1038/nphys3241
Start Year 2015
 
Description Total - Sunpower 
Organisation Total E & P
Country Unknown 
Sector Private 
PI Contribution Singlet fission photon multipler research
Collaborator Contribution Sunpower part of the Total group is the 2nd largest Si PV manufacturer in the world. They are providing us Si modules and solar glass samples to test our photon multipler film on
Impact Currently confidential
Start Year 2016
 
Title Composite Light Harvesting Material and Device 
Description Device to enhance the efficiency of solar cells. 
IP Reference WO2016009203 
Protection Patent application published
Year Protection Granted
Licensed Yes
Impact Parter company has raised investment to commercialise the technology