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Royal Academy of Engineering Research Fellow

BE(Hons) The University of Auckland
PhD University of Cambridge

Optoelectronic materials

My research focuses on creating semiconductors that tolerate defects, with applications in electronics requiring high performance to be achieved using low-cost manufacturing methods, such as photovoltaics, ultrahigh definition displays and solar-fuels production. My work strongly couples the basic science of understanding defect-tolerance to the engineering of device performance from new materials with advanced techniques and structures. I focus on developing scalable growth methods with the ultimate aim of implementing the new optoelectronic materials in industry.

Defect-tolerant semiconductors

Materials that are defect-tolerant are characterised by shallow defect levels in the band gap, high dielectric constants and low effective masses. This results in the defects being more benign, which relaxes constraints in how carefully the material needs to be synthesised. A recent example of a class of successful defect-tolerant materials is halide perovskites. While thin films have high defect densities of 1015–1016 cm-3, most defects are benign, and devices from these materials have increased in efficiency at a higher rate than traditional semiconductors. However, these perovskites contain lead, and there are concerns over the environmental impact of the widescale-deployment of perovskite optoelectronic devices. My research focuses on developing design rules for defect tolerance and applying these to identify, grow and develop new classes of lead-free materials, with particular focus on photovoltaics. One recent example is bismuth oxyiodide (BiOI).

Tandem Photovoltaics

Silicon solar cells constitute 94% of world production, but their deployment is constrained by the high cost of manufacturing. A solution to this is to stack a low-cost solar cell (ideally 1.7–1.9 eV) with a wider band gap on top in a tandem architecture. This can increase efficiencies without significantly increasing cost, resulting in lower levelised-cost-of-electricity, which can enable greater deployment. Previously, I developed an ITO/NiOx recombination contact, which coupled perovskite top-cells with industry-dominant p-type silicon bottom cells for the first time in a two-terminal architecture (IEEE J. Photovolt., 8, 1023–1028 (2018)). Working with a group in Stanford, we used this recombination contact in perovskite tandems with the more efficient silicon heterojunction cell, resulting in a certified 23.6% efficiency and 1000 h device stability (Nat. Energy, 2, 17009 (2017)). My research will focus on making tandems with lead-free defect-tolerant solar cells, as well as refining tandem architectures.

Printing Oxides by Atmospheric Pressure Chemical Vapour Deposition

Realising low-cost optoelectronics commercially requires high-throughput synthesis methods. We have developed an atmospheric pressure chemical vapour deposition (AP-CVD) reactor that grows oxides two orders of magnitude faster than industry-standard atomic layer deposition, but with similar quality. My research focuses on using this reactor to grow oxides with tailored energy levels to achieve high performance in optoelectronic devices, such as charge injectors for light emitting diodes and transparent conducting oxides for photovoltaics.​

 

Cross-sectional scanning electron microscopy image and performance of bismuth oxyiodide (BiOI) photovoltaics. The BiOI absorber is grown by chemical vapour transport and contacted with p-type NiOx and n-type ZnO to selectively extract holes and electron respectively after illumination from the substrate at the bottom. An external quantum efficiency (ratio of photons converted to electrons) of up to 80% is reached, the highest for any bismuth-based solar cell at the time of publication. Adv. Mater., 29, 1702176 (2017). 

 

  • R. L. Z. Hoye, L. Eyre, F. Wei, F. Brivio, A. Sadhanala, S. Sun, W. Li, K. H. L. Zhang, J. L. MacManus-Driscoll, P. D. Bristowe, R. H. Friend, A. K. Cheetham, and F. Deschler. "Fundamental Carrier Lifetime Exceeding 1 µs in Cs2AgBiBr6 Double Perovskite", Advanced Materials Interfaces, 5, 1800464 (2018). DOI: 10.1002/admi.201800464.
  • R. L. Z. Hoye, L. C. Lee, R. C. Kurchin, T. N. Huq, K. H. L. Zhang, M. Sponseller, L. Nienhaus, R. E. Brandt, J. Jean, J. A. Polizzotti, A. Kursumović, M. G. Bawendi, V. Bulović, V. Stevanović, T. Buonassisi, and J. L. MacManus-Driscoll. "Strongly Enhanced Photovoltaic Performance and Defect Physics of Air-Stable Bismuth Oxyiodide (BiOI)", Advanced Materials, 29, 1702176 (2017). DOI: 10.1002/adma.201702176. Highlighted in press release [https://www.cam.ac.uk/research/news/non-toxic-alternative-for-next-generation-solar-cells]
  • R. L. Z. Hoye, P. Schulz, L. T. Schelhas, A. M. Holder, K. H. Stone, J. D. Perkins, D. Vigil-Fowler, S. Siol, D. O. Scanlon, A. Zakutayev, A. Walsh, I. C. Smith, B. C. Melot, R. C. Kurchin, Y. Wang, J. Shi, F. C. Marques, J. J. Berry, W. Tumas, S. Lang, V. Stevanovic, M. F. Toney, and T. Buonassisi. "Perovskite-Inspired Photovoltaic Materials: Toward Best Practices in Materials Characterization and Calculations", Chemistry of Materials, 29, 1964–1988 (2017). DOI: 10.1021/acs.chemmater.6b03852. Highlighted in ACS special issue on lead-free perovskites and listed in sample of best research from Chemistry of Materials.
  • R. L. Z. Hoye, M. R. Chua, K. P. Musselman, G. Li, M.-L. Lai, Z.-K. Tan, N. C. Greenham, J. L. MacManus-Driscoll, R. H. Friend, and D. Credgington. "Enhanced Performance in Fluorene-Free Organometal Halide Perovskite Light-Emitting Diodes using Tunable, Low Electron Affinity Oxide Electron Injectors", Advanced Materials, 27(8), 1414–1419 (2015). DOI: 10.1002/adma.201405044.
  • R. L. Z. Hoye, B. Ehrler, M. L. Böhm, D. Muñoz-Rojas, R. M. Altamimi, A. Y. Alyamani, Y. Vaynzof, A. Sadhanala, G. Ercolano, N. C. Greenham, R. H. Friend, J. L. MacManus-Driscoll, and K. P. Musselman. "Improved Open - Circuit Voltage in ZnO - PbSe Quantum Dot Solar Cells by Understanding and Reducing Losses Arising from the ZnO Conduction Band Tail", Advanced Energy Materials, 4, 1301544 (2014). DOI: 10.1002/adma.201405044.