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CMP
Credit: Jack Hobhouse

Robert Oliver (he/him)

Graduate Student

Research theme

  • Photovoltaics and nanoscience

Sub department

  • Condensed Matter Physics

Research groups

  • Photovoltaic and optoelectronic device group
  • Terahertz photonics
robert.oliver@physics.ox.ac.uk
Telephone: 01865 (2)82329
Robert Hooke Building, room G30
  • About
  • Publications

Thermally stable passivation toward high efficiency inverted perovskite solar cells

ACS Energy Letters American Chemical Society 5:11 (2020) 3336-3343

Authors:

Robert DJ Oliver, Yen-Hung Lin, Alexander J Horn, Chelsea Q Xia, Jonathan H Warby, Michael B Johnston, Alexandra J Ramadan, Henry J Snaith

Abstract:

Although metal halide perovskite photovoltaics have shown an unprecedented rise in power conversion efficiency (PCE), they remain far from their theoretical PCE limit. Among the highest efficiencies to date are delivered when polycrystalline films are enhanced via “molecular passivation”, but this can introduce new instabilities, in particular under severe accelerated aging conditions (e.g., at 85 °C in the dark or under full spectrum simulated sunlight). Here, we utilize a benzylammonium bromide passivation treatment to improve device performance, achieving the champion stabilized power output (SPO) of 19.5 % in a p-i-n device architecture. We correlate the improved device performance with a significant increase in charge carrier diffusion lengths, mobilities, and lifetimes. Furthermore, treated devices maintain an increased performance during 120 h combined stressing under simulated full spectrum sunlight at 85 °C, indicating that enhancement from this passivation treatment is sustained under harsh accelerated aging conditions. This is a crucial step toward real-world operation-relevant passivation treatments.
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Revealing the origin of voltage loss in mixed-halide perovskite solar cells

Energy and Environmental Science Royal Society of Chemistry 13 (2019) 258-267

Authors:

Suhas Mahesh, JM Ball, RDJ Oliver, DP McMeekin, P Nayak, MB Johnston, H Snaith

Abstract:

The tunable bandgap of metal-halide perovskites has opened up the possibility of tandem solar cells with over 30% efficiency. Iodide-Bromide (I-Br) mixed-halide perovskites are crucial to achieve the optimum bandgap for such tandems. However, when the Br content is increased to widen the bandgap, cells fail to deliver the expected increase in open-circuit voltage (VOC). This loss in VOC has been attributed to photo-induced halide segregation. Here, we combine Fourier Transform Photocurrent Spectroscopy (FTPS) with detailed balance calculations to quantify the voltage loss expected from the halide segregation, providing a means to quantify the VOC losses arising from the formation of low bandgap iodide-rich phases during halide segregation. Our results indicate that, contrary to popular belief, halide segregation is not the dominant VOC loss mechanism in Br-rich wide bandgap cells. Rather, the loss is dominated by the relatively low initial radiative efficiency of the cells, which arises from both imperfections within the absorber layer, and at the perovskite/charge extraction layer heterojunctions. We thus identify that focussing on maximising the initial radiative efficiency of the mixed-halide films and devices is more important than attempting to suppress halide segeregation. Our results suggest that a VOC of up to 1.33 V is within reach for a 1.77 eV bandgap perovskite, even if halide segregation cannot be supressed
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A piperidinium salt stabilizes efficient metal-halide perovskite solar cells

Science American Association for the Advancement of Science 369:6499 (2020) 96-102

Authors:

Yen-Hung Lin, Nobuya Sakai, Peimei Da, Jiaying Wu, Harry Sansom, Alexandra Ramadan, Suhas Mahesh, Junliang Liu, Robert Oliver, Jongchul Lim, Lee Aspitarte, Kshama Sharma, Pk Madhu, Anna Morales‐Vilches, Pabitra Nayak, Sai Bai, Feng Gao, Christopher Grovenor, Michael Johnston, John Labram, James Durrant, James Ball, Bernard Wenger, Bernd Stannowski, Henry Snaith

Abstract:

Longevity has been a long-standing concern for hybrid perovskite photovoltaics. We demonstrate high-resilience positive-intrinsic-negative perovskite solar cells by incorporating a piperidiniumbased ionic-compound into the formamidinium-cesium lead-trihalide perovskite absorber. With the band gap tuned to be well suited for perovskite-on-silicon tandem cells, this piperidinium additive enhances the open-circuit voltage and cell efficiency. This additive also retards compositional segregation into impurity phases and pinhole formation in the perovskite absorber layer during aggressive aging. Under full-spectrum simulated sunlight in ambient atmosphere, our Confidential unencapsulated and encapsulated cells retain 80% and 95% of their peak and “post-burn-in” efficiencies for 1010 and 1200 hours at 60 and 85 degree Celsius, respectively. Our analysis reveals detailed degradation routes that contribute to the failure of aged cells.
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Visualizing Macroscopic Inhomogeneities in Perovskite Solar Cells

ACS Energy Letters American Chemical Society (ACS) (2022) 2311-2322

Authors:

Akash Dasgupta, Suhas Mahesh, Pietro Caprioglio, Yen-Hung Lin, Karl-Augustin Zaininger, Robert DJ Oliver, Philippe Holzhey, Suer Zhou, Melissa M McCarthy, Joel A Smith, Maximilian Frenzel, M Greyson Christoforo, James M Ball, Bernard Wenger, Henry J Snaith
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Scalable processing for realizing 21.7%-efficient all-perovskite tandem solar modules.

Science (New York, N.Y.) 376:6594 (2022) 762-767

Authors:

Ke Xiao, Yen-Hung Lin, Mei Zhang, Robert DJ Oliver, Xi Wang, Zhou Liu, Xin Luo, Jia Li, Donny Lai, Haowen Luo, Renxing Lin, Jun Xu, Yi Hou, Henry J Snaith, Hairen Tan

Abstract:

Challenges in fabricating all-perovskite tandem solar cells as modules rather than as single-junction configurations include growing high-quality wide-bandgap perovskites and mitigating irreversible degradation caused by halide and metal interdiffusion at the interconnecting contacts. We demonstrate efficient all-perovskite tandem solar modules using scalable fabrication techniques. By systematically tuning the cesium ratio of a methylammonium-free 1.8-electron volt mixed-halide perovskite, we improve the homogeneity of crystallization for blade-coated films over large areas. An electrically conductive conformal "diffusion barrier" is introduced between interconnecting subcells to improve the power conversion efficiency (PCE) and stability of all-perovskite tandem solar modules. Our tandem modules achieve a certified PCE of 21.7% with an aperture area of 20 square centimeters and retain 75% of their initial efficiency after 500 hours of continuous operation under simulated 1-sun illumination.
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