Cambridge-AMOLF Collaboration on Photonic and Optoelectronic Control of Thin-Film LEDs and Solar Cells

Lead Research Organisation: University of Cambridge
Department Name: Physics

Abstract

This Centre-to-Centre collaboration addresses a set of research opportunities that require the close integration of optoelectronic materials and device engineering with state-of-the-art light management for large area solar cells and LEDs. The collaboration brings the AMOLF LMPV group, recognised for its work in 'light management' for solar cells, to work closely with the Cambridge research programme on thin-film perovskite and organic solar cells and LEDs. The AMOLF activity is centred in the very strong 'national laboratory' framework of solar cell research in the Netherlands, and brings strengths that have not been systematically developed in the UK.

Thin-film diodes made with lead halide perovskites now support solar cells and LEDs with excellent electronic properties, but challenges with light in/outcoupling can limit performance. This is a particular challenge for perovskite LEDs for which light outcoupling is currently limited to 20%. By harnessing the special luminescent properties of perovskites, including photon recycling, with engineered optical structures, the outcoupling in the forward direction will be raised towards 100%.

One way to improve a solar cell beyond the single-junction limit is to harvest the high-energy part of the solar spectrum with an organic material capable of singlet fission, a process by which the energy from one high-energy photon is shared between two lower-energy triplet exciton states. Cambridge has pioneered the science of singlet fission and developed the concept of the Photon Multiplier. In this all-optical thin-film device, incident high-energy photons (<540nm) will be converted into two low-energy photons, each at around 1000 nm, which can then be absorbed by a silicon solar cell underneath. The challenge to be undertaken here is to develop suitable photonic designs that direct the emission of these IR photons towards the Si solar cell without introducing optical losses in the module.

Planned Impact

This collaborative project will lead to an improvement in the performance of thin-film LEDs and solar cells, achieved through integrated design of the electronic and optical operation. The potential for improved performance covers perovskite solar cells and perovskite LEDs. The LEDs are currently limited by poor light out-coupling, but there is the potential to raise their external quantum efficiencies above that of other thin film LED technologies. A further component of the project is the design and implementation of optimised optical coupling between a light-absorbing, 'photon multiplier' film above a silicon solar cell, so that infra-red photons generated in the film are directed to and absorbed in the silicon below. All these projects are grounded in basic science, but have very considerable industrial and commercial consequence:

Improvement in the efficiency of solar cells is now considered critical to reducing the cost of solar electricity, since the balance of systems costs now outweigh the costs of the solar cell itself. Our work on solar cells will provide significant efficiency enhancements, and hence will accelerate the deployment of photovoltaic systems with attendant economic and environmental benefits. The consortium is well-placed through our interactions with UK and European companies and national laboratories to ensure that these benefits are realised locally. Cambridge already has a strong IP position in the 'photon multiplier' area, which will be further enhanced through this project and will allow direct economic benefit in the UK via IP licensing. There is a real potential for UK manufacturing of the 'photon multiplier' films that can be supplied to global PV module manufacturers.

Perovskite LEDs were pioneered in Cambridge, and their rapid improvement in performance has lifted them to commercial significance. Further improvements in performance, including those delivered by this project, will accelerate their commercialisation. IP will build on the substantial base already established. In partnership with collaborators at the University of Oxford, Cambridge has founded a start-up company, Heliochrome, as a vehicle for IP in this area, and to address the initial challenges of commercialisation.
 
Description This project explores the electro-optical properties of thin-film solar cell and LED devices and in particular, the management of light absorption and/or extraction. To date, we have explored the importance of photon re-absorption processes (aka photon recycling) on the operation of lead halide perovskite semiconductors. We find that this process is particularly important for this class of semiconductors, and we have explored the role this plays in a range of thin film LED devices structures. We have also investigated a wide range of deposition and crystallisation conditions for the perovskites.
Exploitation Route too early
Sectors Electronics

Energy

 
Description House of Lords Committee - 2023
Geographic Reach National 
Policy Influence Type Participation in a guidance/advisory committee
 
Title Data Supporting: Tunable Multiband Halide Perovskite Tandem Photodetectors with Switchable Response 
Description Data supporting the publication entitled "Tunable Multiband Halide Perovskite Tandem Photodetectors with Switchable Response" This data set includes information on the modelling of the photodetector behaviour, calculating the impact of perovskite band gap and thickness. The dataset contains the data of the optimisation of narrowband detection performance, using EQE scans. The charactersation of photodetector performance, including noise and response speed. Finally, data on the demonstration of an encrypted comms. method is contained. All data was obtained as CSV files and processed in excel 
Type Of Material Database/Collection of data 
Year Produced 2023 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/346715
 
Title Data for: Relaxed current matching requirements in highly luminescent perovskite tandem solar cells and their fundamental efficiency limits 
Description Figure 1 contains data for the limiting efficiency of a Shockley-Queisser tandem solar cell, with and without luminescence coupling included in simulations. Figure 2 contains decay data from transient absorption spectroscopy and photoluminescence quantum efficiency measurements for the halide perovskite thin film FA0.7Cs0.3Pb(I0.7Br0.3)3. It also contains absorption coefficient and (real) refractive index for both FA0.7Cs0.3Pb(I0.7Br0.3)3 and FAPb0.5Sn0.5I3 thin films, as measured by a combination of ellipsometry, photothermal deflection spectroscopy and Ubach tail fitting. Figure 3 contans the absorbance of FAPb0.5Sn0.5I3 in an idealised tandem stack with FA0.7Cs0.3Pb(I0.7Br0.3)3, the limiting efficiency of this stack as a function of thickness without and with luminescence coupling included in simulations, and the difference in power generated throughout the year without and with luminescence coupling for a typical spectral year on the Canada/USA border from these modelled solar cells. Figure 4 contains the limiting efficiency of the all-perovskite tandem as a function of charge trapping rate (for optimised thicknesses) with luminescence coupling, and a ratio of this result to a second simulation including luminescnece coupling. Figure 5 explores an experimental all-perovskite tandem solar cell. It contains the photoluminescence emission (relative to that at open-circuit voltage) of the high-bandgap sub-cell as a function of applied voltage when illuminated by a 405nm laser, the microscopic photoluminescence from a cross section of the tandem when excited by a 636nm laser, the photolumiescence from a cross section of this region when only the high-bandgap sub-cell is excited, and the time resolve photoluminescence of this emission. 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/316458
 
Title Research data supporting "Computational Study of Dipole Radiation in Re-absorbing Perovskite Semiconductors for Optoelectronics" 
Description Excel file with tabs containing the data for each Figure in the paper: Figure 1: (c) Refractive index (N = n+j?) and internal radiation spectrum of FAPbI3 perovskite used in the simulation. (d) Relative amounts of dipole energy (at m = 10 and ? = 800 nm) which are outcoupled, re-absorbed by emitter (Aact), or re-absorbed by parasitic layers (Apara), as a function of relative radial propagation vector kr/ks. For kr > ks, the dipole is non-radiatively coupled with nearby parasitic absorbers (surface plasmon polariton (SPP) mode) or the emitter itself. (e) Fraction of photon propagation in various modes: outcoupling, re-absorption within escape cone, waveguide trapping, substrate trapping, and non-radiative parasitic dissipation (SPP), as a function of wavelength. The non-outcoupled radiative modes are split into Aact and Apara, depending on the final destination of photons. Figure 2: (b) Calculated direct outcoupling ratio of photons emitted in a perovskite LED, having a structure of glass (1 mm)/ ITO (150 nm)/ ZnO (30 nm)/ FAPbI3 perovskite (50 nm)/ TFB (40 nm)/ MoO3 (7 nm)/ Au (100 nm), for the calculations using various kr resolutions, represented by kr step over ks. c) Monochromatically (? = 800 nm) calculated direct outcoupling ratio of photons emitted in a perovskite film, having a structure of glass (incoherent)/ perovskite (50 nm), assuming a complex perovskite refractive index of Ns = 2.55 + j?s. Figure 4: Simulation results for FAPbI3-based perovskite LEDs. (a) Relative ratio of the photon propagation through various modes of outcoupling, re-absorption within escape cone, waveguide trapping, substrate trapping, and non-radiative parasitic dissipation (SPP), as a function of perovskite thickness. The non-outcoupled radiative modes are split into Aact and Apara, depending on the final destination of photons. (b) Depth (z)-profile of internal radiation which is finally outcoupled (i.e. relative contribution to EQEmax), for LEDs with 10 nm-thick (grey), 30 nm-thick (red), 120 nm-thick (green), and 200 nm-thick (blue) perovskites. (c) The relative internal angular dipole intensity in perovskites LED with different emissive layer thickness (top) and relative intensity of horizontal dipole (Dx) over vertical dipole (Dz) monochromatically calculated in a single film (Ns = 2.55+0.068j at 800 nm). (d) Calculated LEE (= EQE / ?inj ?rad) as a function of internal radiation efficiency (?rad). (dashed line: ray-optics limit of 1/2n2) e) EQEmax for the LED at a single wavelength of 800 nm with n = 2.55 and various ? values of the 200 nm-thick perovskite emissive layer. Figure 5: Variation of TFB optical spacer (between perovskite and MoO3/Au) thickness in a perovskite LED having a 50 nm-thick FAPbI3 as an emissive layer. a) Relative ratio of the photon propagation through various modes as a function of TFB thickness. b-c) Relative external emission as a function of angle in the air mode for various wavelengths, for b) 40 nm and c) 320 nm-thick TFB layers. Figure 6: Calculated mode fractions and EQEmax for perovskite LEDs varying (a) ZnO thickness and (c-d) luminescence spectrum, depicted in (b). Perovskite thickness is 50, 30, 200 nm, for a), c), d), respectively. 
Type Of Material Database/Collection of data 
Year Produced 2020 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/312804
 
Title Research data supporting 'Imaging Light-Induced Migration of Dislocations in Halide Perovskites with 3D Nanoscale Strain Mapping' 
Description Research data supporting "Imaging Light-Induced Migration of Dislocations in Halide Perovskites with 3D Nanoscale Strain Mapping". The .zip file contains all the data required to reproduce the main text and supporting figures. For more details see the read_me files located in the main folder and also subfolders. The primary data types are raw diffraction data (intensity counts per pixel) from Bragg coherent diffraction imaging scans performed at the I13-1 beamline of the Diamond Light Source Synchrotron in Didcot, UK. These data are in stacked .tif file format and are all organised according to the figure in which they are used. These tif stacks can then be reconstructed into real space objects ("reconstructions") using the MatLab code provided in the "reconstruction code" folder with instructions on how to use the code are contained in this folder's "read_me.txt" file. Data characterising the dislocations found in this work are generated though analysis of the dislocation-containing reconstructions according to the method outlined in the manuscript. This analysis was performed using Paraview software. The other data contained in this file are from photoluminescence microscopy measurements performed in Stranks group labs in Cambridge. Detailed equipment specifications and measurement methods are given in the linked manuscript. Hyperspectral mapping data is in .h5 format which can be opened using python and we recommend using the HyperSpy package linked in the relevant "read_me.txt" files. Time-resolved photoluminescence data are provided in .csv format for ease of plotting. 
Type Of Material Database/Collection of data 
Year Produced 2023 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/358048
 
Title Research data supporting 'Investigation of singlet fission-halide perovskite interfaces'. 
Description Experimental data of change of tetracene and halide perovskite photoluminescence with applied magnetic field, a spectrum of a bilayer and time resolved photoluminescence when exiting and measuring at different wavelengths. Modelling results of: i) The change in the density functional theory (DFT)-level bandgap with number of repeating tetracene units in different directions and associated inputs and outputs from DFT codes. ii) Input and output of calculations DFT and post-DFT calculations of singlet and triplet states in bulk tetracene. iii) The change in the DFT-level bandgap of CsPbI3 with number of repeating units, for both CsI and PbI2 terminations. Associated input and outputs from DFT calculations. iv) Projected density of states for a tetracene molecule on the surface of a halide perovskite (with different orientations). Associated input and outputs from DFT calculations. v) Projected density of states for tetracene/halide perovskite bilayers (with different orientations of tetracene and surface terminations of the halide perovskite). Associated input and outputs from DFT calculations. vi) The difference in DFT and post-DFT energy levels calculated for toy models of tetracene on halide perovskite (both CsI and PbI2 surface terminations). Associated input and outputs from DFT and post-DFT calculations. 
Type Of Material Database/Collection of data 
Year Produced 2022 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/336768
 
Title Research data supporting: "Quantifying photon recycling in solar cells and light emitting diodes: absorption and emission are always key" 
Description Figure 1 plots the number of photon recycling events per initial excitation versus photoluminescence quantum efficiency and escape probability, calculated from equation 6 given in manuscript. Figures 2 and 3 model photon recycling in methylammonium lead iodide solar cells. Figure 2 shows the number of photon recycling at maximum power point events versus; thickness (with no charge trapping); charge trapping rate (for a 500nm film); and as a fucntion of front transmission and back reflection coefficients (for a 500nm film). The inset in Figure 2a shows corresponding information to 2a, but at open circuit. Figure 3 shows number of photon recycling events versus efficiency, both as a function of charge trapping rate for a 500nm film, for a film which interacts with a 2*pi hemisphere and 2.5 degrees solid angle about the sun in a) and c) respectively. b) shows the current-voltage curves for some situations described in a) (for no charge trapping, 500nm film). Figure 4 models photon recycling in caesium lead bromide light emittiong diodes. Figure 4: a shows the number of photon recycling events versus thickness (with no charge trapping); b shows the number of photon recycling events versus voltage for different charge trapping rates (for a 100nm film); c the number of photon recycling events versus front transmission and back reflection coefficients (for a 100nm thick film and no charge trapping). Figure 4d presents normalised photoluminescence for three absorption models considered; and e and f the number of photon recycling events versus emitted light (luminous emittance or luminance respectively) both as a function of voltage, for three different emittance models considered, for emission into a 2*pi hemisphere (e) or 2.5 degree solid angle (f), both for a 100nm thin film. 
Type Of Material Database/Collection of data 
Year Produced 2020 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/307708
 
Description Cambridge AMOLF Centre-to-Centre collaboration 
Organisation FOM Institute AMOLF
Country Netherlands 
Sector Public 
PI Contribution This is an EPSRC Centre-to-Centre grant that enables a collaborative programme between Cambridge and AMOLF in the field of photonics of thin film PV and LED devices
Collaborator Contribution Post-doctoral researchers supported by this grant are working in both institutions
Impact Grimaldi et al. "Microstructuring of 2D perovskites via ion-exchange fabrication", Appl. Phys. Lett. 119, 223102 (2021); https://doi.org/10.1063/5.0065070 McGovern et al. "Reduced Barrier for Ion Migration in Mixed-Halide Perovskites" ACS Appl. Energy Mater. 2021, 4, 12, 13431-13437 https://doi.org/10.1021/acsaem.1c03095
Start Year 2019
 
Description Cambridge Festival 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Engaging general public in making solar cells from berries, and general solar cell, lighting and detector research
Year(s) Of Engagement Activity 2022,2023
URL https://www.ceb.cam.ac.uk/news/camfest#:~:text=our%20YouTube%20channel.-,2023,style%20of%20tradition...