Sargent, Ted

Permanent URI for this collectionhttps://hdl.handle.net/1807/69841

Ted Sargent received the B.Sc.Eng. (Engineering Physics) from Queen's University in 1995 and the Ph.D. in Electrical and Computer Engineering (Photonics) from the University of Toronto in 1998. He has held the following visiting professorships:

MIT: Visiting Professor, Nanotechnology and Photonics, in the Microphotonics Center, MIT, 2004-5

UCLA: Fulbright Visiting Professor at UCLA 2013

Berkeley: Somorjai Visiting Miller Professorship at Berkeley Fall 2017

He holds the rank of University Professor in the Edward S. Rogers Sr. Department of Electrical and Computer Engineering at the University of Toronto. He holds the Canada Research Chair in Nanotechnology and also serves as Vice President-International for the University of Toronto.

His book The Dance of Molecules: How Nanotechnology is Changing Our Lives (Penguin) was published in Canada and the United States in 2005 and has been translated into French, Spanish, Italian, Korean, and Arabic.

He is founder and CTO of InVisage Technologies and a co-founder of Xagenic.

He is a Fellow of the Royal Society of Canada; a Fellow of the AAAS “...for distinguished contributions to the development of solar cells and light sensors based on solution-processed semiconductors;” and a Fellow of the IEEE “... for contributions to colloidal quantum dot optoelectronic devices.” He is Fellow of the Canadian Academy of Engineering for “…ground-breaking research in nanotechnology, applying novel quantum-tuned materials to the realization of full-spectrum solar cells and ultra sensitive light detectors. The impact of his work has been felt in industry through his formation of two start-up companies."

His publications have been cited over 27,000 times [Scopus].

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Diamine chelates for increased stability in mixed Sn–Pb and all-perovskite tandem solar cells
(Nature Research, 2024-08-15) Li, Chongwen; Chen, Lei; Jiang, Fangyuan; Song, Zhaoning; Wang, Xiaoming; Balvanz, Adam; Ugur, Esma; Liu, Yuan; Liu, Cheng; Maxwell, Aidan; Chen, Hao; Liu, Yanjiang; Wang, Zaiwei; Xia, Pan; Li, You; Fu, Sheng; Sun, Nannan; Grice, Corey R.; Wu, Xuefei; Fink, Zachary; Hu, Qin; Zeng, Lewei; Jung, Euidae; Wang, Junke; Park, So Min; Luo, Deying; Chen, Cailing; Shen, Jie; Han, Yu; Perini, Carlo Andrea Riccardo; Correa-Baena, Juan-Pablo; Lu, Zheng-Hong; Russell, Thomas P.; De Wolf, Stefaan; Kanatzidis, Mercouri G.; Ginger, David S.; Chen, Bin; Yan, Yanfa; Sargent, Edward H.
Perovskite tandem solar cells show promising performance, but non-radiative recombination and its progressive worsening with time, especially in the mixed Sn–Pb low-bandgap layer, limit performance and stability. Here we find that mixed Sn–Pb perovskite thin films exhibit a compositional gradient, with an excess of Sn on the surface—and we show this gradient exacerbates oxidation and increases the recombination rate. We find that diamines preferentially chelate Sn atoms, removing them from the film surface and achieving a more balanced Sn:Pb stoichiometry, making the surface of the film resistive to the oxidation of Sn. The process forms an electrically resistive low-dimensional barrier layer, passivating defects and reducing interface recombination. Further improving the homogeneity of the barrier layer using 1,2-diaminopropane results in more uniform distribution and passivation. Tandems achieve a power conversion efficiency of 28.8%. Encapsulated tandems retain 90% of initial efficiency following 1,000 h of operating at the maximum power point under simulated one-sun illumination in air without cooling.
The dynamic adsorption affinity of ligands is a surrogate for the passivation of surface defects
(Nature Research, 2024-03-06) Xu, Jian; Maxwell, Aidan; Song, Zhaoning; Bati, Abdulaziz S R; Chen, Hao; Li, Chongwen; Park, So Min; Yan, Yanfa; Chen, Bin; Sargent, Edward H
Surface defects in semiconducting materials, though they have been widely studied, remain a prominent source of loss in optoelectronic devices; here we sought a new angle of approach, looking into the dynamic roles played by surface defects under atmospheric stressors and their chemical passivants in the lifetime of optoelectronic materials. We find that surface defects possess properties distinct from those of bulk defects. ab initio molecular dynamics simulations reveal a previously overlooked reversible degradation mechanism mediated by hydrogen vacancies. We find that dynamic surface adsorption affinity (DAA) relative to surface treatment ligands is a surrogate for passivation efficacy, a more strongly-correlated feature than is the static binding strength emphasized in prior reports. This guides us to design targeted passivator ligands with high molecular polarity: for example, 4-aminobutylphosphonic acid exhibits strong DAA and provides defect passivation applicable to a range of perovskite compositions, including suppressed hydrogen vacancy formation, enhanced photovoltaic performances and operational stability in perovskite solar cells.
2D Hybrid Perovskites Employing an Organic Cation Paired with a Neutral Molecule
(ACS, 2023-12-20) Najarian, Amin Morteza; Vafaie, Maral; Sabatini, Randy; Wang, Sasa; Li, Peng; Xu, Shihong; Saidaminov, Makhsud I; Hoogland, Sjoerd; Sargent, Edward H
Two-dimensional (2D) hybrid perovskites harness the chemical and structural versatility of organic compounds. Here, we explore 2D perovskites that incorporate both a first organic component, a primary ammonium cation, and a second neutral organic module. Through the experimental examination of 42 organic pairs with a range of functional groups and organic backbones, we identify five crystallization scenarios that occur upon mixing. Only one leads to the cointercalation of the organic modules with distinct and extended interlayer spacing, which is observed with the aid of X-ray diffraction (XRD) pattern analysis combined with cross-sectional transmission electron microscopy (TEM) and elemental analysis. We present a picture in which complementary pairs, capable of forming intermolecular bonds, cocrystallize with multiple structural arrangements. These arrangements are a function of the ratio of organic content, annealing temperature, and substrate surface characteristics. We highlight how noncovalent bonds, particularly hydrogen and halogen bonding, enable the influence over the organic sublattice in hybrid halide perovskites.
What does net zero by 2050 mean to the solar energy materials researcher?
(Cell Press, 2022-05-04) Chen, Bin; Sargent, Edward H.
The energy sector is today the largest greenhouse gas emitter, accounting for ∼70% of anthropogenic CO2 emissions. Rigorous decarbonization of the global energy supply is required to limit the temperature rise to below 1.5°C and reach net zero by 2050. Solar photovoltaics will play a key role, and massive upscaling of solar photovoltaics is faced with many challenges. Here we discuss how materials researchers can contribute to this global grand challenge.
Suppressed phase segregation for triple-junction perovskite solar cells
(Nature Research, 2023-03-28) Wang, Zaiwei; Zeng, Lewei; Zhu, Tong; Chen, Hao; Chen, Bin; Kubicki, Dominik J; Balvanz, Adam; Li, Chongwen; Maxwell, Aidan; Ugur, Esma; Dos Reis, Roberto; Cheng, Matthew; Yang, Guang; Subedi, Biwas; Luo, Deying; Hu, Juntao; Wang, Junke; Teale, Sam; Mahesh, Suhas; Wang, Sasa; Hu, Shuangyan; Jung, Eui Dae; Wei, Mingyang; Park, So Min; Grater, Luke; Aydin, Erkan; Song, Zhaoning; Podraza, Nikolas J; Lu, Zheng-Hong; Huang, Jinsong; Dravid, Vinayak P; De Wolf, Stefaan; Yan, Yanfa; Grätzel, Michael; Kanatzidis, Merx G; Sargent, Edward H
The tunable bandgaps and facile fabrication of perovskites make them attractive for multi-junction photovoltaics1,2. However, light-induced phase segregation limits their efficiency and stability3-5: this occurs in wide-bandgap (>1.65 electron volts) iodide/bromide mixed perovskite absorbers, and becomes even more acute in the top cells of triple-junction solar photovoltaics that require a fully 2.0-electron-volt bandgap absorber2,6. Here we report that lattice distortion in iodide/bromide mixed perovskites is correlated with the suppression of phase segregation, generating an increased ion-migration energy barrier arising from the decreased average interatomic distance between the A-site cation and iodide. Using an approximately 2.0-electron-volt rubidium/caesium mixed-cation inorganic perovskite with large lattice distortion in the top subcell, we fabricated all-perovskite triple-junction solar cells and achieved an efficiency of 24.3 per cent (23.3 per cent certified quasi-steady-state efficiency) with an open-circuit voltage of 3.21 volts. This is, to our knowledge, the first reported certified efficiency for perovskite-based triple-junction solar cells. The triple-junction devices retain 80 per cent of their initial efficiency following 420 hours of operation at the maximum power point.
CO2 electroreduction to multicarbon products from carbonate capture liquid
(Elsevier, 2023-05-26) Lee, Geonhui; Rasouli, Armin Sedighian; Lee, Byoung-Hoon; Zhang, Jinqiang; Won, Da Hye; Xiao, Yurou Celine; Edwards, Jonathan P.; Lee, Mi Gyoung; Jung, Eui Dae; Arabyarmohammadi, Fatemeh; Liu, Hengzhou; Grigioni, Ivan; Abed, Jehad; Alkayyali, Tartela; Liu, Shijie; Xie, Ke; Miao, Rui Kai; Park, Sungjin; Dorakhan, Roham; Zhao, Yong; O’Brien, Colin P.; Chen, Zhu; Sinton, David; Sargent, Edward
Alkali hydroxide systems capture CO2as carbonate; however, generating a pure CO2stream requires significant energy input, typically from thermal cycling to 900 C. What is more, the subsequent valorization of gas-phase CO2into products presents additional energy requirements and system complexities, including man-aging the formation of (bi)carbonate in an electrolyte and separating unreacted CO2downstream. Here, we report the direct electrochemical conversion of CO2, captured in the form of carbon-ate, into multicarbon (C2+) products. Using an interposer and a Cu/CoPc-CNTs electrocatalyst, we achieve 47% C2+Faradaic efficiency at 300 mA cm 2and a full cell voltage of 4.1 V. We report 56 wt % ofC2H4and no detectable C1gas in the product gas stream: CO, CH4,and CO2combined total below 0.9 wt % (0.1 vol %). This approach obviates the need for energy to regenerate lost CO2, an issue seen in prior CO2-to-C2+reports
Rational design of Lewis base molecules for stable and efficient inverted perovskite solar cells
(American Association for the Advancement of Science, 2023-02-16) Li, Chongwen; Wang, Xiaoming; Bi, Enbing; Jiang, Fangyuan; Park, So Min; Li, You; Chen, Lei; Wang, Zaiwei; Zeng, Lewei; Chen, Hao; Liu, Yanjiang; Grice, Corey R; Abudulimu, Abasi; Chung, Jaehoon; Xian, Yeming; Zhu, Tao; Lai, Huagui; Chen, Bin; Ellingson, Randy J; Fu, Fan; Ginger, David S; Song, Zhaoning; Sargent, Edward H; Yan, Yanfa
Lewis base molecules that bind undercoordinated lead atoms at interfaces and grain boundaries (GBs) are known to enhance the durability of metal halide perovskite solar cells (PSCs). Using density functional theory calculations, we found that phosphine-containing molecules have the strongest binding energy among members of a library of Lewis base molecules studied herein. Experimentally, we found that the best inverted PSC treated with 1,3-bis(diphenylphosphino)propane (DPPP), a diphosphine Lewis base that passivates, binds, and bridges interfaces and GBs, retained a power conversion efficiency (PCE) slightly higher than its initial PCE of ~23% after continuous operation under simulated AM1.5 illumination at the maximum power point and at ~40°C for >3500 hours. DPPP-treated devices showed a similar increase in PCE after being kept under open-circuit conditions at 85°C for >1500 hours.
Electron-Transport Layers Employing Strongly Bound Ligands Enhance Stability in Colloidal Quantum Dot Infrared Photodetectors
(Wiley, 2022-09-22) Zhang, Yangning; Vafaie, Maral; Xu, Jian; Pina, Joao M; Xia, Pan; Najarian, Amin M; Atan, Ozan; Imran, Muhammad; Xie, Ke; Hoogland, Sjoerd; Sargent, Edward H
Solution-processed photodetectors based on colloidal quantum dots (CQDs) are promising candidates for short-wavelength infrared light sensing applications. Present-day CQD photodetectors employ a CQD active layer sandwiched between carrier-transport layers in which the electron-transport layer (ETL) is composed of metal oxides. Herein, a new class of ETLs is developed using n-type CQDs, finding that these benefit from quantum-size effect tuning of the band energies, as well as from surface ligand engineering. Photodetectors operating at 1450 nm are demonstrated using CQDs with tailored functionalities for each of the transport layers and the active layer. By optimizing the band alignment between the ETL and the active layer, CQD photodetectors that combine a low dark current of ≈1 × 10-3 mA cm-2 with a high external quantum efficiency of ≈66% at 1 V are reported, outperforming prior reports of CQD photodetectors operating at >1400 nm that rely on metal oxides as ETLs. It is shown that stable CQD photodetectors rely on well-passivated CQDs: for ETL CQDs, a strongly bound organic ligand trans-4-(trifluoromethyl)cinnamic acid (TFCA) provides improved passivation compared to the weakly bound inorganic ligand tetrabutylammonium iodide (TBAI). TFCA suppresses bias-induced ion migration inside the ETL and improves the operating stability of photodetectors by 50× compared to TBAI.
Quantum-size-tuned heterostructures enable efficient and stable inverted perovskite solar cells
(Nature Research, 2022-04-07) Chen, Hao; Teale, Sam; Chen, Bin; Hou, Yi; Grater, Luke; Zhu, Tong; Bertens, Koen; Park, So Min; Atapattu, Harindi R.; Gao, Yajun; Wei, Mingyang; Johnston, Andrew K.; Zhou, Qilin; Xu, Kaimin; Yu, Danni; Han, Congcong; Cui, Teng; Jung, Eui Hyuk; Zhou, Chun; Zhou, Wenjia; Proppe, Andrew H.; Hoogland, Sjoerd; Laquai, Frédéric; Filleter, Tobin; Graham, Kenneth R.; Ning, Zhijun; Sargent, Edward H.
The energy landscape of reduced-dimensional perovskites (RDPs) can be tailored by adjusting their layer width (n). Recently, two/three-dimensional (2D/3D) heterostructures containing n = 1 and 2 RDPs have produced perovskite solar cells (PSCs) with >25% power conversion efficiency (PCE). Unfortunately, this method does not translate to inverted PSCs due to electron blocking at the 2D/3D interface. Here we report a method to increase the layer width of RDPs in 2D/3D heterostructures to address this problem. We discover that bulkier organics form 2D heterostructures more slowly, resulting in wider RDPs; and that small modifications to ligand design induce preferential growth of n ≥ 3 RDPs. Leveraging these insights, we developed efficient inverted PSCs (with a certified quasi-steady-state PCE of 23.91%). Unencapsulated devices operate at room temperature and around 50% relative humidity for over 1,000 h without loss of PCE; and, when subjected to ISOS-L3 accelerated ageing, encapsulated devices retain 92% of initial PCE after 500 h.
Strong-Proton-Adsorption Co-Based Electrocatalysts Achieve Active and Stable Neutral Seawater Splitting
(Wiley, 2023-01-31) Wang, Ning; Ou, Pengfei; Hung, Sung-Fu; Huang, Jianan Erick; Ozden, Adnan; Abed, Jehad; Grigioni, Ivan; Chen, Clark; Miao, Rui Kai; Yan, Yu; Zhang, Jinqiang; Wang, Ziyun; Dorakhan, Roham; Badreldin, Ahmed; Abdel-Wahab, Ahmed; Sinton, David; Liu, Yongchang; Liang, Hongyan; Sargent, Edward H
Direct electrolysis of pH-neutral seawater to generate hydrogen is an attractive approach for storing renewable energy. However, due to the anodic competition between the chlorine evolution and the oxygen evolution reaction (OER), direct seawater splitting suffers from a low current density and limited operating stability. Exploration of catalysts enabling an OER overpotential below the hypochlorite formation overpotential (≈490 mV) is critical to suppress the chloride evolution and facilitate seawater splitting. Here, a proton-adsorption-promoting strategy to increase the OER rate is reported, resulting in a promoted and more stable neutral seawater splitting. The best catalysts herein are strong-proton-adsorption (SPA) materials such as palladium-doped cobalt oxide (Co3- x Pdx O4 ) catalysts. These achieve an OER overpotential of 370 mV at 10 mA cm-2 in pH-neutral simulated seawater, outperforming Co3 O4 by a margin of 70 mV. Co3- x Pdx O4 catalysts provide stable catalytic performance for 450 h at 200 mA cm-2 and 20 h at 1 A cm-2 in neutral seawater. Experimental studies and theoretical calculations suggest that the incorporation of SPA cations accelerates the rate-determining water dissociation step in neutral OER pathway, and control studies rule out the provision of additional OER sites as a main factor herein.
Bifunctional Electron-Transporting Agent for Red Colloidal Quantum Dot Light-Emitting Diodes
(ACS, 2023-03-10) Wang, Ya-Kun; Wan, Haoyue; Xu, Jian; Zhong, Yun; Jung, Eui Dae; Park, So Min; Teale, Sam; Imran, Muhammad; Yu, You-Jun; Xia, Pan; Won, Yu-Ho; Kim, Kwang-Hee; Lu, Zheng-Hong; Liao, Liang-Sheng; Hoogland, Sjoerd; Sargent, Edward H
Indium phosphide (InP) quantum dots have enabled light-emitting diodes (LEDs) that are heavy-metal-free, narrow in emission linewidth, and physically flexible. However, ZnO/ZnMgO, the electron-transporting layer (ETL) in high-performance red InP/ZnSe/ZnS LEDs, suffers from high defect densities, quenches luminescence when deposited on InP, and induces performance degradation that arises due to trap migration from the ETL to the InP emitting layer. We posited that the formation of Zn2+ traps on the outer ZnS shell, combined with sulfur and oxygen vacancy migration between ZnO/ZnMgO and InP, may account for this issue. We synthesized therefore a bifunctional ETL (CNT2T, 3',3'″,3'″″-(1,3,5-triazine-2,4,6-triyl)tris(([1,1'-biphenyl]-3-carbonitrile)) designed to passivate Zn2+ traps locally and in situ and to prevent vacancy migration between layers: the backbone of the small molecule ETL contains a triazine electron-withdrawing unit to ensure sufficient electron mobility (6 × 10-4 cm2 V-1 s-1), and the star-shaped structure with multiple cyano groups provides effective passivation of the ZnS surface. We report as a result red InP LEDs having an EQE of 15% and a luminance of over 12,000 cd m-2; this represents a record among organic-ETL-based red InP LEDs.
Redox-mediated electrosynthesis of ethylene oxide from CO2 and water
(Nature Research, 2022-02-24) Li, Yuhang; Ozden, Adnan; Leow, Wan Ru; Ou, Pengfei; Huang, Jianan Erick; Wang, Yuhang; Bertens, Koen; Xu, Yi; Liu, Yuan; Roy, Claudie; Jiang, Hao; Sinton, David; Li, Chunzhong; Sargent, Edward H.
The electrochemical production of ethylene oxide (EO) from CO2, water and renewable electricity could result in a net consumption of CO2. Unfortunately existing electrochemical CO2-to-EO conversions show impractical Faradaic efficiency (FE) and require a high energy input. Here we report a class of period-6-metal-oxide-modified iridium oxide catalysts that enable us to achieve improved CO2-to-EO conversion. Among barium, lanthanum, cerium and bismuth, we find that barium-oxide-loaded catalysts achieve an ethylene-to-EO FE of 90%. When we pair this with the oxygen reduction reaction at the cathode, we achieve an energy input of 5.3 MJ per kg of EO, comparable to that of existing (emissions-intensive) industrial processes. We have also devised a redox-mediated paired system that shows a 1.5-fold higher CO2-to-EO FE (35%) and uses a 1.2 V lower operating voltage than literature benchmark electrochemical systems.
All-perovskite tandem solar cells with improved grain surface passivation
(Nature Research, 2022-01-17) Lin, Renxing; Xu, Jian; Wei, Mingyang; Wang, Yurui; Qin, Zhengyuan; Liu, Zhou; Wu, Jinlong; Xiao, Ke; Chen, Bin; Park, So Min; Chen, Gang; Atapattu, Harindi R; Graham, Kenneth R; Xu, Jun; Zhu, Jia; Li, Ludong; Zhang, Chunfeng; Sargent, Edward H; Tan, Hairen
All-perovskite tandem solar cells hold the promise of surpassing the efficiency limits of single-junction solar cells; however, until now, the best-performing all-perovskite tandem solar cells have exhibited lower certified efficiency than have single-junction perovskite solar cells. A thick mixed Pb-Sn narrow-bandgap subcell is needed to achieve high photocurrent density in tandem solar cells, yet this is challenging owing to the short carrier diffusion length within Pb-Sn perovskites. Here we develop ammonium-cation-passivated Pb-Sn perovskites with long diffusion lengths, enabling subcells that have an absorber thickness of approximately 1.2 μm. Molecular dynamics simulations indicate that widely used phenethylammonium cations are only partially adsorbed on the surface defective sites at perovskite crystallization temperatures. The passivator adsorption is predicted to be enhanced using 4-trifluoromethyl-phenylammonium (CF3-PA), which exhibits a stronger perovskite surface-passivator interaction than does phenethylammonium. By adding a small amount of CF3-PA into the precursor solution, we increase the carrier diffusion length within Pb-Sn perovskites twofold, to over 5 μm, and increase the efficiency of Pb-Sn perovskite solar cells to over 22%. We report a certified efficiency of 26.4% in all-perovskite tandem solar cells, which exceeds that of the best-performing single-junction perovskite solar cells. Encapsulated tandem devices retain more than 90% of their initial performance after 600 h of operation at the maximum power point under 1 Sun illumination in ambient conditions.
High carbon utilization in CO2 reduction to multi-carbon products in acidic media
(Nature Research, 2022-06-09) Xie, Yi; Ou, Pengfei; Wang, Xue; Xu, Zhanyou; Li, Yuguang C.; Wang, Ziyun; Huang, Jianan Erick; Wicks, Joshua; McCallum, Christopher; Wang, Ning; Wang, Yuhang; Chen, Tianxiang; Lo, Benedict T. W.; Sinton, David; Yu, Jimmy C.; Wang, Ying; Sargent, Edward H.
Renewable electricity-powered CO2 reduction to multi-carbon (C2+) products offers a promising route to realization of low-carbon-footprint fuels and chemicals. However, a major fraction of input CO2 (>85%) is consumed by the electrolyte through reactions with hydroxide to form carbonate/bicarbonate in both alkaline and neutral reactors. Acidic conditions offer a solution to overcoming this limitation, but also promote the hydrogen evolution reaction. Here we report a design strategy that suppresses hydrogen evolution reaction activity by maximizing the co-adsorption of CO and CO2 on Cu-based catalysts to weaken H* binding. Using density functional theory studies, we found Pd–Cu promising for selective C2+ production over C1, with the lowest ∆GOCCOH* and ∆GOCCOH* - ∆GCHO*. We synthesized Pd–Cu catalysts and report a crossover-free system (liquid product crossover <0.05%) with a Faradaic efficiency of 89 ± 4% for CO2 to C2+ at 500 mA cm−2, simultaneous with single-pass CO2 utilization of 60 ± 2% to C2+.
Synthesis-on-substrate of quantum dot solids
(Nature Research, 2022-12-21) Jiang, Yuanzhi; Sun, Changjiu; Xu, Jian; Li, Saisai; Cui, Minghuan; Fu, Xinliang; Liu, Yuan; Liu, Yaqi; Wan, Haoyue; Wei, Keyu; Zhou, Tong; Zhang, Wei; Yang, Yingguo; Yang, Jien; Qin, Chaochao; Gao, Shuyan; Pan, Jun; Liu, Yufang; Hoogland, Sjoerd; Sargent, Edward H; Chen, Jun; Yuan, Mingjian
Perovskite light-emitting diodes (PeLEDs) with an external quantum efficiency exceeding 20% have been achieved in both green and red wavelengths; however, the performance of blue-emitting PeLEDs lags behind. Ultrasmall CsPbBr3 quantum dots are promising candidates with which to realize efficient and stable blue PeLEDs, although it has proven challenging to synthesize a monodispersed population of ultrasmall CsPbBr3 quantum dots, and difficult to retain their solution-phase properties when casting into solid films. Here we report the direct synthesis-on-substrate of films of suitably coupled, monodispersed, ultrasmall perovskite QDs. We develop ligand structures that enable control over the quantum dots' size, monodispersity and coupling during film-based synthesis. A head group (the side with higher electrostatic potential) on the ligand provides steric hindrance that suppresses the formation of layered perovskites. The tail (the side with lower electrostatic potential) is modified using halide substitution to increase the surface binding affinity, constraining resulting grains to sizes within the quantum confinement regime. The approach achieves high monodispersity (full-width at half-maximum = 23 nm with emission centred at 478 nm) united with strong coupling. We report as a result blue PeLEDs with an external quantum efficiency of 18% at 480 nm and 10% at 465 nm, to our knowledge the highest reported among perovskite blue LEDs by a factor of 1.5 and 2, respectively.
A silver–copper oxide catalyst for acetate electrosynthesis from carbon monoxide
(Nature Research, 2023-03-13) Dorakhan, Roham; Grigioni, Ivan; Lee, Byoung-Hoon; Ou, Pengfei; Abed, Jehad; O’Brien, Colin; Sedighian Rasouli, Armin; Plodinec, Milivoj; Miao, Rui Kai; Shirzadi, Erfan; Wicks, Joshua; Park, Sungjin; Lee, Geonhui; Zhang, Jinqiang; Sinton, David; Sargent, Edward H.
Acetic acid is an important chemical feedstock. The electrocatalytic synthesis of acetic acid from CO2 offers a low-carbon alternative to traditional synthetic routes, but the direct reduction from CO2 comes with a CO2 crossover energy penalty. CO electroreduction bypasses this, which motivates the interest in a cascade synthesis approach of CO2 to CO followed by CO to acetic acid. Here we report a catalyst design strategy in which off-target intermediates (such as ethylene and ethanol) in the reduction of CO to acetate are destabilized. On the optimized Ag–CuO2 catalyst, this destabilization of off-target intermediates leads to an acetate Faradaic efficiency of 70% at 200 mA cm−2. We demonstrate 18 hours of stable operation in a membrane electrode assembly; the system produced 5 wt% acetate at 100 mA cm−2 and a full-cell energy efficiency of 25%, a twofold improvement on the highest energy-efficient electrosynthesis in prior reports.
Supramolecular tuning of supported metal phthalocyanine catalysts for hydrogen peroxide electrosynthesis
(Nature Research, 2023-03-13) Lee, Byoung-Hoon; Shin, Heejong; Rasouli, Armin Sedighian; Choubisa, Hitarth; Ou, Pengfei; Dorakhan, Roham; Grigioni, Ivan; Lee, Geonhui; Shirzadi, Erfan; Miao, Rui Kai; Wicks, Joshua; Park, Sungjin; Lee, Hyeon Seok; Zhang, Jinqiang; Chen, Yuanjun; Chen, Zhu; Sinton, David; Hyeon, Taeghwan; Sung, Yung-Eun; Sargent, Edward H.
Two-electron oxygen reduction offers a route to H2O2 that is potentially cost-effective and less energy-intensive than the industrial anthraquinone process. However, the catalytic performance of the highest performing prior heterogeneous electrocatalysts to H2O2 has lain well below the >300 mA cm−2 needed for capital efficiency. Herein, guided by computation, we present a supramolecular approach that utilizes oxygen functional groups in a carbon nanotube substrate that—when coupled with a cobalt phthalocyanine catalyst—improve cobalt phthalocyanine adsorption, preventing agglomeration; and that further generate an electron-deficient Co centre whose interaction with the key H2O2 intermediate is tuned towards optimality. The catalysts exhibit an overpotential of 280 mV at 300 mA cm−2 with turnover frequencies over 50 s−1 in a neutral medium, an order of magnitude higher activity compared with the highest performing prior H2O2 electrocatalysts. This performance is sustained for over 100 h of operation.
Interpretable discovery of semiconductors with machine learning
(2023-06-29) Choubisa, Hitarth; Todorović, Petar; Pina, Joao M.; Parmar, Darshan H.; Li, Ziliang; Voznyy, Oleksandr; Tamblyn, Isaac; Sargent, Edward H.
Machine learning models of material properties accelerate materials discovery, reproducing density functional theory calculated results at a fraction of the cost1,2,3,4,5,6. To bridge the gap between theory and experiments, machine learning predictions need to be distilled in the form of interpretable chemical rules that can be used by experimentalists. Here we develop a framework to address this gap by combining evolutionary algorithm-powered search with machine-learning surrogate models. We then couple the search results with supervised learning and statistical testing. This strategy enables the efficient search of a materials space while providing interpretable design rules. We demonstrate its effectiveness by developing rules for the design of direct bandgap materials, stable UV emitters, and IR perovskite emitters. Finally, we conclusively show how DARWIN-generated rules are statistically more robust and applicable to a wide range of applications including the design of UV halide perovskites.
Germanium silicon oxide achieves multi-coloured ultra-long phosphorescence and delayed fluorescence at high temperature
(2022-08-01) Chen, Huai; Wei, Mingyang; He, Yantao; Abed, Jehad; Teale, Sam; Sargent, Edward H; Yang, Zhenyu
Colour-tuned phosphors are promising for advanced security applications such as multi-modal anti-counterfeiting and data encryption. The practical adoption of colour-tuned phosphors requires these materials to be responsive to multiple stimuli (e.g., excitation wavelength, excitation waveform, and temperature) and exhibit excellent materials stability simultaneously. Here we report germanium silicon oxide (GSO) - a heavy-metal-free inorganic phosphor - that exhibits colour-tuned ultra-long phosphorescence and delayed fluorescence across a broad temperature range (300 - 500 K) in air. We developed a sol-gel processing strategy to prepare amorphous oxides containing homogeneously dispersed Si and Ge atoms. The co-existence of Ge and Si luminescent centres (LC) leads to an excitation-dependent luminescence change across the UV-to-visible region. GSO exhibits Si LC-related ultra-long phosphorescence at room-temperature and thermally activated delayed fluorescence at temperatures as high as 573 K. This long-lived PL is sensitized via the energy transfer from Ge defects to Si LCs, which provides PL lifetime tunability for GSO phosphors. The oxide scaffold of GSO offers 500-day materials stability in air; and 1-week stability in strong acidic and basic solutions. Using GSO/polymer hybrids, we demonstrated colour-tuned security tags whose emission wavelength and lifetime can be controlled via the excitation wavelength, and temperature, indicating promise in security applications.
Sub-millimetre light detection and ranging using perovskites
(2022) Morteza Najarian, Amin; Vafaie, Maral; Johnston, Andrew; Zhu, Tong; Wei, Mingyang; Saidaminov, Makhsud I.; Hou, Yi; Hoogland, Sjoerd; García de Arquer, F. Pelayo; Sargent, Edward H.
Light detection and ranging (LiDAR) technology is an active remote-sensing system used in autonomous vehicles, machine vision and augmented reality. Improvements in the speed and signal-to-noise ratio of photodetectors are needed to meet these demanding ranging applications. Silicon electronics have been the principal option for LiDAR photodetectors in the range of 850–950 nm. However, its indirect bandgap leads to a low absorption coefficient in the near-infrared region, as well as a consequent trade-off between speed and efficiency. Here we report solution-processed lead–tin binary perovskite photodetectors that have an external quantum efficiency of 85% at 850 nm, dark current below 10–8 A cm–2 and response time faster than 100 ps. The devices are fabricated using self-limiting and self-reduced tin precursors that enable perovskite crystallization at the desired stoichiometry and prevent the formation of interfacial defects with the hole transport layer. The approach removes oxygen from the solution, converts Sn4+ to Sn2+ through comproportionation, and leaves neither metallic tin nor SnOx residues. To illustrate the potential of these solution-processed perovskite photodetectors in LiDAR, we show that they can resolve sub-millimetre distances with a typical 50 µm standard deviation.

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