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 - Insights into the nature of charge and energy transfer at organic-inorganic and organic-organic heterojunctions
- new experimental methods to study the above
Exploitation Route Formation of a new spin-out company, Cambridge Photon Technology : https://www.cambridgephoton.com/
Several new lines of research have been opened by our work and are being pursued by a large number of groups around the world
Sectors Energy

 
Description Formation of a new spin-out company, Cambridge Photon Technology : https://www.cambridgephoton.com/ The company has raised >£1M in funding and employs 8 people at present.
Sector Energy,Manufacturing, including Industrial Biotechology
Impact Types Societal

Economic

 
Description House of Lords Committee - 2023
Geographic Reach National 
Policy Influence Type Participation in a guidance/advisory committee
 
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 09/2016 
End 03/2020
 
Description PhD Studentship - PV CDT
Amount £80,000 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 09/2017 
End 09/2021
 
Description PhD Studentships - 4 in total - Limeng Ni, Ture Hinrichsen, Jesse Allardice, Arya Thampi
Amount £500,000 (GBP)
Organisation Cambridge Commonwealth Trust 
Sector Academic/University
Country United Kingdom
Start 09/2015 
End 03/2019
 
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 Belgium
Start 03/2018 
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 Public
Country United Kingdom
Start 03/2017 
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 Public
Country United Kingdom
Start 06/2015 
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 Data supporting "A Molecular Movie of Ultrafast Singlet Fission " 
Description This data set contains all data underlying the figures in the main text and supporting information. The information on how the data was acquired and processed is detailed in the open access manuscript + SI which has been deposited in this repository ("A Molecular Movie of Singlet Fission") and is also available open-access via the publisher Nature Communications under the same title. Main Figures: Figure 1 - Transient absorption data on DP-Mes and transient cuts Figure 2 - Fourier transform power map of the data in Figure 1 as well as complementary Raman spectra for comparison Figure 3 - Comparison of directly generated and 'transferred' vibrational coherence spectrum Figure 4 - Theoretical modelling of the collective vibrational coherences separated according to symmetry groups. The data was converted into a quasi-resonance Raman spectrum and compared to the data in Figure 3. Figure 5 - Extracted structural parameters (bond length and dihedral angle) as function of time as well as the correlation of the displacement coherences for tuning and coupling modes are shown. SI Figures: Figure S6 - contains the Fourier amplitude spectrum of the tuning modes retrieved from theory (not resonance Raman) Figure S7 - provides the maximum displacement amplitudes as a function of frequency for the B1 coupling modes Figure S8 - displays the S1 decay dynamics from theory as a function of modifying the coupling modes as well as the extraced exponential decay dynamics. Figure S9 - contains the transient absorption spectrum of DP-Mes (a) compared to TIPS-pentacene (b) as well as a comparison of the direct and transferred coherence properties of DP-Mes (c) and TIPS-pentacene (d). The transferred spectrum of TIPS is compared to the transferred and direct spectrum of DP-Mes in e Figure S10 - Full time evolution from theory of the S1 and 1TT population dynamics (a), central dimer bond length (b) and dihedral angle (c) Figure S11 - Temperature Dependence of transient absorption measurements in DP-Mes at 295 K (a) and 5 K (b). The dynamics for S1 (c) and 1TT (d) as a function of temperature are also give.n Video: The video is a smoothed representation of the time-dependent structure extracted from theory. all structures are saved after each other in the conventional xyz file format. These are best opened with a molecular editor such as Avogadro or VMD. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/296198
 
Title Data supporting "Direct Observation of Ultrafast Singlet Exciton Fission in Three Dimensions" 
Description This data set contains all data underlying the figures in the main text and supporting information. The information on how the data was acquired and processed is detailed in the open access manuscript + SI which has been deposited in this repository and is also available open-access via the publisher Nature Communications under the title "Direct Observation of Ultrafast Singlet Exciton Fission in Three Dimensions". All the extracted data can also be generated from the experimental data by running the model described in the Main text. Main Figures: Fig 1 - b) Transient transmission and complex refractive index slices of pentacene, c) z-stack dependent transient transmission images of pentacene on two spectral bands radially averaged, d) image of the sample of pentacene on hBN. Fig 2,3 and 4 - Underlying datasets of transient transmission images (DTT) on glass and on hBN are provided in two folders 'onGlass' and 'onhBN'. In each the DTTs.npy file is meant to be opened using the python numpy library and the numpy.load command, yielding a 3 dimensional array, where the first axis is time and the second and third axis index X and Y position. The time.txt file give the pump probe delay corresponding to the first axis index. Each pixel (X and Y) corresponds to 55.5 nm in real space. The glass dataset is radially averaged to provide Fig 2/3/4 a and the radial slices in Fig 2/3/4 b (the full images are plotted above it). Upon fitting the radial averaged to the model described in the main text with appropriate bounds yields Fig 2/3/4 d-g. 
Type Of Material Database/Collection of data 
Year Produced 2022 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/341252
 
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: Ultrafast melting and recovery of collective order in the excitonic insulator Ta2NiSe5 
Description This data includes that which is shown in the main text figures 1-4 of the associated publication. We have used pump-probe measurements to investigate the ordered phase in excitonic insulator candidate, Ta2NiSe5. The measurements are performed with a single pump, and two pump configuration (also sometimes called pump-push-probe). While all the data shown is taken in reflection, we did similar measurements also in a transmission configuration. 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/316859
 
Title Research data supporting "Directed Energy Transfer from Monolayer WS2 to Near Infrared Emitting PbS-CdS Quantum Dots" 
Description Optical characterisation data of 2D/QD heterostructure. i.e. steady state photoluminescence, absorption data of monolayer WS2, PbS-CdS quantum dots and WS2/PbS-CdS heterostructure; Time resolved PL of WS2, PbS-CdS and WS2/PbS-CdS heterostructure. Each data set is entitled with figure name in article i.e Main_Fig1c-e_SI_Fig3 contains raw data and figures for Figure 1c-e in main article and figure 3 in Supplementary information (SI) Main_Fig2_b-e_SI_Fig1-2 contains raw data and figures for Figure 2b-e in main article and figures 1-2 in Supplementary information (SI) Main_Fig_2a_RHS contains raw data for Figure 2a in main article Main_Fis_2a_RHS_processed contains figure for Figure 2a in main article Main_Fig3_Main_Fig5 contains raw data and figures for Figure 3 and 5 in the main article Main_Fig4 contains raw data and figures for Figure 4 in the main article 
Type Of Material Database/Collection of data 
Year Produced 2020 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/311242
 
Title Research data supporting "Engineering Molecular Ligand Shells on Quantum Dots for Quantitative Harvesting of Triplet Excitons Generated by Singlet Fission" 
Description This dataset consists of graphical and tabular data in an Origin file format. The file includes UV-Vis absorption, PLQE, kinetic modelling, transient PL and absorption, steady-state PL and excitation spectra and magnetic field dependent PL measurement data and analysis. Further information about the data collection methods and analysis is available via the journal JACS, at 10.1021/jacs.9b06584. The Origin file "Analysis.opju" contains the data for all plots presented in the paper and SI titled "Engineering Molecular Ligand Shells on Quantum Dots for Quantitative Harvesting of Triplet Excitons Generated by Singlet Fission", along with additional data surrounding the analysis of the presented data. The file is separated into folders sorted by experiment. Figures used in the paper are prefixed with either "Main Fig" or "SI" followed by a brief description of the figure. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
 
Title Research data supporting "Nanoscale Chemical Heterogeneity Dominates the Optoelectronic Response of Alloyed Perovskite Solar Cells" 
Description This repository contains the data required to reproduce the figures from the associated manuscript. This data includes hyperspectral optical imaging cubes, nano X-ray fluorescence and diffraction maps and transient absorption microscopy data. 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/329908
 
Title Research data supporting "Real-Time Observation of Exciton-Phonon Coupling Dynamics in Self-Assembled Hybrid Perovskite Quantum Wells" 
Description Absorption, PL, PDS, TA and FFT data 
Type Of Material Database/Collection of data 
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  
 
Title Research data supporting ''Imaging the coherent propagation of collective modes in the excitonic insulator Ta2NiSe5 at room temperature'' 
Description Using a widefield pump-probe microscope (with ~10 nm spatial precision and ~10 fs time resolution) we probe the temperature and fluence dependent dynamics of the collective modes in excitonic insulator candidate Ta2NiSe5. We pump with a broadband pulse centered around 500 nm and probe ~800 nm using a bandpass filter. 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/329004
 
Title Research data supporting Giant photoluminescence enhancement in MoSe2 monolayers treated with oleic acid ligands 
Description Main_Fig1b-d_SI_Fig8: Photoluminescence scatter data, Meidan PL spectra absolute, Median PL spectra scaled to compare FWHM; and Raman spectra Main_Fig2a-d_Fig3a-f: PL intensity series spectra, PL intensity series, relative PLQE series and; PL species characterization Main_Fig4a-b_SI_Fig5a-b_SI_Fig6: Time resolved PL spectra, Time resolved PL fluence series and; all Time resolved PL spectra from series Main_Fig5a: Transistor transfer characteristics Main_Fig5b: Transistor threshold voltage Main_Fig5c: Transistor sub-threshold swing Main_Fig5d: Transistor on/off ratio SI_Fig1: PL spectra of WS2 monolayers washed with toluene SI_Fig3-4_All_data: PL spectra from intensity series fitted with Gaussians SI_Fig7: Oleic Acid treated tungsten diselenide spectra 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/324063
 
Title Research data supporting Understanding the Photoluminescence Quenching of Liquid Exfoliated WS2 Monolayers 
Description The dataset comprises Origin files that contain the data underlying the figures in the manuscript. The data can be easily traced from the respective spectra in the same Origin file. Origin file "fig 2" contains both the raw data, normalized data, fitting data and absorption and photoluminescence spectra used in Figure 2. The absorption spectra are fitted to the second derivative of two Lorenzians after smoothing the spectrum with the Lowess method. Book 4 in the Origin file "fig 2" is a summary of the parameters and equations used in the fitting process. The x-axis is the wavelength (nm) and y-axis is the count. Different samples are all labelled in the first row for both raw and normalized absorption and photoluminescence data. Origin file "fig 3 a,b" contains both the raw data, normalized data, pump-probe spectra and kinetics used in Figure 3. The x-axis (col(a)) is the wavelength (nm) for pump-probe spectra, and equation "col(a)-315" is used to define the time 0 in the manuscript. The different time is labelled in the first row. The x-axis is the time (fs) for kinetics. The names for x and y axis for data in figure 4 are labelled in the first row. 
Type Of Material Database/Collection of data 
Year Produced 2022 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/344330
 
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 United Kingdom 
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 A photovoltaic device comprising a light harvesting device and a photovoltaic cell; wherein the light harvesting device comprises an organic semiconductor photoactive layer capable of multiple exciton generation with a luminescent material dispersed therein; wherein the bandgap of the luminescent material is selected such that the triplet excitons, formed as a result from the multiple exciton generation in the organic semiconductor, can be transferred from the organic semiconductor into the luminescent material non-radiatively via Dexter Energy Transfer; a photovoltaic cell disposed in an emissive light path of the luminescent material and having a first photoactive layer, wherein the bandgap of the luminescent material matches or is higher than the bandgap of the first photoactive layer. 
IP Reference WO2016009203 
Protection Patent application published
Year Protection Granted 2016
Licensed Yes
Impact Parter company has raised investment to commercialise the technology
 
Company Name Cambridge Photon Technology 
Description Cambridge Photon Technology designs and manufactures its Photon Multiplier Film, which is nanotechnology that enables solar photovoltaic cells to capture energy more efficiently. 
Year Established 2019 
Impact RSC Emerging Technologies Prize Deep Tech Pioneers Award- Hello Tomorrow Global Challenge Cambridge Photon Technology have been named one of six national finalists in the 2019 Shell Springboard competition.
Website https://www.cambridgephoton.com/