Imperial College London


Faculty of EngineeringDepartment of Chemical Engineering

Facility Manager - Automated High-throughput Materials Synt







ACEX 210AACE ExtensionSouth Kensington Campus





Publication Type

7 results found

Jagt RA, Huq TN, Börsig KM, Sauven D, Lee LC, MacManus-Driscoll JL, Hoye RLZet al., 2020, Controlling the preferred orientation of layered BiOI solar absorbers, Journal of Materials Chemistry C, Vol: 15 jun 2020, Pages: 10791-10797, ISSN: 2050-7526

Bismuth oxyiodide (BiOI) has gained attention for photovoltaics, photocatalysis and photodetectors owing to its composition of non-toxic elements, tolerance to point defects, and highly-suitable optical properties. But like many other bismuth-based compounds, BiOI is a layered material with anisotropic transport properties, making control over the preferred orientation critical for achieving optimal device performance. In this work, we develop new insights into the growth mechanism of BiOI synthesized by chemical vapor deposition (CVD) and show how the preferred orientation can be controlled. By adjusting the precursor and substrate temperatures to tune whether or not we are in a nucleation- or growth-controlled regime, we reproducibly vary the ratio of the (001) and (110) orientations by over two orders of magnitude. As a result, we achieve highly c-axis oriented films, which leads to less shunting than a/b-axis oriented films, resulting in improved open-circuit voltages from a median value of 0.7 V (a/b-axis oriented) to 0.9 V (c-axis oriented) in BiOI solar cells. More broadly, the described mechanisms can be used to control the preferred orientation in other low-dimensional materials, which will be important for achieving improved performance across a wide variety of devices.

Journal article

Huq T, Lee L, Eyre L, Li W, Jagt R, Kim C, Fearn S, Pecunia V, Deschler F, MacManus-Driscoll J, Hoye Ret al., 2020, Electronic structure and optoelectronic properties of bismuth Ooxyiodide robust against percent-level iodine-, oxygen- and bismuth-related surface defects, Advanced Functional Materials, Vol: 30, Pages: 1-11, ISSN: 1616-301X

In the search for nontoxic alternatives to lead‐halide perovskites, bismuth oxyiodide (BiOI) has emerged as a promising contender. BiOI is air‐stable for over three months, demonstrates promising early‐stage photovoltaic performance and, importantly, is predicted from calculations to tolerate vacancy and antisite defects. Here, whether BiOI tolerates point defects is experimentally investigated. BiOI thin films are annealed at a low temperature of 100 °C under vacuum (25 Pa absolute pressure). There is a relative reduction in the surface atomic fraction of iodine by over 40%, reduction in the surface bismuth fraction by over 5%, and an increase in the surface oxygen fraction by over 45%. Unexpectedly, the Bi 4f7/2 core level position, Fermi level position, and valence band density of states of BiOI are not significantly changed. Further, the charge‐carrier lifetime, photoluminescence intensity, and the performance of the vacuum‐annealed BiOI films in solar cells remain unchanged. The results show BiOI to be electronically and optoelectronically robust to percent‐level changes in surface composition. However, from photoinduced current transient spectroscopy measurements, it is found that the as‐grown BiOI films have deep traps located ≈0.3 and 0.6 eV from the band edge. These traps limit the charge‐carrier lifetimes of BiOI, and future improvements in the performance of BiOI photovoltaics will need to focus on identifying their origin. Nevertheless, these deep traps are three to four orders of magnitude less concentrated than the surface point defects induced through vacuum annealing. The charge‐carrier lifetimes of the BiOI films are also orders of magnitude longer than if these surface defects were recombination active. This work therefore shows BiOI to be robust against processing conditions that lead to percent‐level iodine‐, bismuth‐, and oxygen‐related surface defects. This will simplify and reduce the cost of fabricating BiOI‐based electronic devices

Journal article

Moloney J, Tesh O, Singh M, Roberts JW, Jarman JC, Lee LC, Huq TN, Brister J, Karboyan S, Kuball M, Chalker PR, Oliver RA, Massabuau FC-Pet al., 2019, Atomic layer deposited α-Ga<sub>2</sub>O<sub>3</sub> solar-blind photodetectors, JOURNAL OF PHYSICS D-APPLIED PHYSICS, Vol: 52, ISSN: 0022-3727

Journal article

Zhao B, Lee LC, Yang L, Pearson AJ, Lu H, She X-J, Cui L, Zhang KHL, Hoye RLZ, Karani A, Xu P, Sadhanala A, Greenham NC, Friend RH, MacManus-Driscoll JL, Di Det al., 2018, In situ atmospheric deposition of ultrasmooth Nickel Oxide for efficient perovskite solar cells, ACS Applied Materials & Interfaces, Vol: 10, Pages: 41849-41854, ISSN: 1944-8244

Organic–inorganic perovskite solar cells have attracted significant attention due to their remarkable performance. The use of alternative metal-oxide charge-transport layers is a strategy to improving device reliability for large-scale fabrication and long-term applications. Here, we report solution-processed perovskite solar cells employing nickel oxide hole-extraction layers produced in situ using an atmospheric pressure spatial atomic-layer deposition system, which is compatible with high-throughput processing of electronic devices from solution. Our sub-nanometer smooth (average roughness of ≤0.6 nm) oxide films enable the efficient collection of holes and the formation of perovskite absorbers with high electronic quality. Initial solar-cell experiments show a power-conversion efficiency of 17.1%, near-unity ideality factors, and a fill factor of >80% with negligible hysteresis. Transient measurements reveal that a key contributor to this performance is the reduced luminescence quenching trap density in the perovskite/nickel oxide structure.

Journal article

Lee LC, Huq TN, MacManus-Driscoll JL, Hoye RLZet al., 2018, Research Update: Bismuth-based perovskite-inspired photovoltaic materials, APL Materials, Vol: 6, Pages: 084502-1-084502-16

Bismuth-based compounds have recently gained interest as solar absorbers with the potential to have low toxicity, be efficient in devices, and be processable using facile methods. We review recent theoretical and experimental investigations into bismuth-based compounds, which shape our understanding of their photovoltaic potential, with particular focus on their defect-tolerance. We also review the processing methods that have been used to control the structural and optoelectronic properties of single crystals and thin films. Additionally, we discuss the key factors limiting their device performance, as well as the future steps needed to ultimately realize these new materials for commercial applications.

Journal article

Hoye RLZ, Lee LC, Kurchin RC, Huq TN, Zhang KHL, Sponseller M, Nienhaus L, Brandt RE, Jean J, Polizzotti JA, Kursumović A, Bawendi MG, Bulović V, Stevanović V, Buonassisi T, MacManus-Driscoll JLet al., 2017, Strongly enhanced photovoltaic performance and defect physics of air-stable bismuth oxyiodide (BiOI), Advanced Materials, Vol: 29, ISSN: 0935-9648

Bismuth‐based compounds have recently gained increasing attention as potentially nontoxic and defect‐tolerant solar absorbers. However, many of the new materials recently investigated show limited photovoltaic performance. Herein, one such compound is explored in detail through theory and experiment: bismuth oxyiodide (BiOI). BiOI thin films are grown by chemical vapor transport and found to maintain the same tetragonal phase in ambient air for at least 197 d. The computations suggest BiOI to be tolerant to antisite and vacancy defects. All‐inorganic solar cells (ITO|NiOx|BiOI|ZnO|Al) with negligible hysteresis and up to 80% external quantum efficiency under select monochromatic excitation are demonstrated. The short‐circuit current densities and power conversion efficiencies under AM 1.5G illumination are nearly double those of previously reported BiOI solar cells, as well as other bismuth halide and chalcohalide photovoltaics recently explored by many groups. Through a detailed loss analysis using optical characterization, photoemission spectroscopy, and device modeling, direction for future improvements in efficiency is provided. This work demonstrates that BiOI, previously considered to be a poor photocatalyst, is promising for photovoltaics.

Journal article

Brandt RE, Poindexter JR, Gorai P, Kurchin RC, Hoye RLZ, Nienhaus L, Wilson MWB, Polizzotti JA, Sereika R, Žaltauskas R, Lee LC, MacManus-Driscoll JL, Bawendi M, Stevanović V, Buonassisi Tet al., 2017, Searching for “Defect-Tolerant” Photovoltaic Materials: Combined Theoretical and Experimental Screening, Chemistry of Materials, Vol: 29, Pages: 4667-4674, ISSN: 0897-4756

Recently, we and others have proposed screening criteria for “defect-tolerant” photovoltaic (PV) absorbers, identifying several classes of semiconducting compounds with electronic structures similar to those of hybrid lead–halide perovskites. In this work, we reflect on the accuracy and prospects of these new design criteria through a combined experimental and theoretical approach. We construct a model to extract photoluminescence lifetimes of six of these candidate PV absorbers, including four (InI, SbSI, SbSeI, and BiOI) for which time-resolved photoluminescence has not been previously reported. The lifetimes of all six candidate materials exceed 1 ns, a threshold for promising early stage PV device performance. However, there are variations between these materials, and none achieve lifetimes as high as those of the hybrid lead–halide perovskites, suggesting that the heuristics for defect-tolerant semiconductors are incomplete. We explore this through first-principles point defect calculations and Shockley–Read–Hall recombination models to describe the variation between the measured materials. In light of these insights, we discuss the evolution of screening criteria for defect tolerance and high-performance PV materials.

Journal article

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