The Edward S. Rogers Sr. Department of Electrical and Computer Engineering

Permanent URI for this collectionhttps://hdl.handle.net/1807/9951

In 1909 the Department of Electrical Engineering was formed when the School of Practical Science entered the University of Toronto as the Faculty of Applied Science and Engineering. Currently our Department consistently ranks among the top in North America. We have an outstanding faculty of over 75 professors in biomedical, computer, communications, electromagnetics, electronics, energy systems, photonics & systems control; many of our members are international leaders in their field. We are proud of the many awards, fellowships and other forms of recognition that members of the Department have received.

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The Edward S. Rogers Sr. Department of Electrical & Computer Engineering

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AMPERE: automated modular platform for expedited and reproducible electrochemical testing
(Royal Society of Chemistry, 2024-09-26) Abed, Jehad; Bai, Yang; Persaud, Daniel; Kim, Jiheon; Witt, Julia; Hattrick-Simpers, Jason; Sargent, Edward H.
Rapid and reliable electrochemical screening is critical to accelerate the development of catalysts for sustainable energy generation and storage. This paper introduces an automated and modular platform for expedited and reproducible electrochemical testing (AMPERE), designed to enhance the efficiency and reliability of multivariate optimization. The platform integrates a liquid-handling robot with custom-made modular array reactors, offering sample preparation and electrochemical testing in the same platform. Additionally, we use offline inductively coupled plasma optical emission spectroscopy (ICP-OES) to measure metal concentrations in the electrolyte after the reaction, which serves as a proxy for assessing the electrochemical stability. We use the platform to conduct 168 experiments continuously in less than 40 hours to examine the influence of catalyst ink formulation on the performance of Ir, Ru, IrO2, and RuO2 for the oxygen evolution reaction (OER) in acid. We specifically investigate the role of solvent type and concentration, catalyst concentration, and binder content on the performance. We find that Ru/RuO2 catalysts show improvements in activity that are not directly linked to improvements in the electrochemical surface area or inversely correlated to Ru dissolution. This suggests a complex interplay between the catalytic performance of the drop-casted catalyst film and ink formulation. AMPERE simplifies catalyst preparation and testing at large scale, making it faster, more reliable, and accessible for widespread use.
Acid-Stable Cu Cluster Precatalysts Enable High Energy and Carbon Efficiency in CO2 Electroreduction
(ACS, 2024-10-09) Kim, Dongha; Park, Sungjin; Lee, Junwoo; Chen, Yiqing; Li, Feng; Kim, Jiheon; Bai, Yang; Huang, Jianan Erick; Liu, Shijie; Jung, Eui Dae; Lee, Byoung-Hoon; Papangelakis, Panagiotis; Ni, Weiyan; Alkayyali, Tartela; Miao, Rui Kai; Li, Peihao; Liang, Yongxiang; Shayesteh Zeraati, Ali; Dorakhan, Roham; Meira, Debora Motta; Chen, Yanna; Sinton, David; Zhong, Mingjiang; Sargent, Edward H
The electrochemical reduction of CO2 in acidic media offers the advantage of high carbon utilization, but achieving high selectivity to C2+ products at a low overpotential remains a challenge. We identified the chemical instability of oxide-derived Cu catalysts as a reason that advances in neutral/alkaline electrolysis do not translate to acidic conditions. In acid, Cu ions leach from Cu oxides, leading to the deactivation of the C2+-active sites of Cu nanoparticles. This prompted us to design acid-stable Cu cluster precatalysts that are reduced in situ to active Cu nanoparticles in strong acid. Operando Raman and X-ray spectroscopy indicated that the bonding between the Cu cluster precatalyst ligand and in situ formed Cu nanoparticles preserves a high density of undercoordinated Cu sites, resulting in a C2H4 Faradaic efficiency of 62% at a low overpotential. The result is a 1.4-fold increase in energy efficiency compared with previous acidic CO2-to-C2+ electrocatalytic systems.
Resurfacing of InAs Colloidal Quantum Dots Equalizes Photodetector Performance across Synthetic Routes
(ACS, 2024-09-11) Ban, Hyeong Woo; Vafaie, Maral; Levina, Larissa; Xia, Pan; Imran, Muhammad; Liu, Yanjiang; Najarian, Amin Morteza; Sargent, Edward H
The synthesis of highly monodispersed InAs colloidal quantum dots (CQDs) is needed in InAs CQD-based optoelectronic devices. Because of the complexities of working with arsenic precursors such as tris-trimethylsilyl arsine ((TMSi)3As) and tris-trimethylgermyl arsine ((TMGe)3As), several attempts have been made to identify new candidates for synthesis; yet, to date, only the aforementioned two highly reactive precursors have led to excellent photodetector device performance. We begin the present study by investigating the mechanism, finding that the use of the cosurfactant dioctylamine plays a crucial role in producing monodispersed InAs populations. Through quantitative analysis of ligands on the surface of InAs CQDs, we find that (TMGe)3As leads to In-rich characteristics, and we document the presence of an amorphous In-oleate shell on the surface. This we find causes surface defects, and thus, we develop materials processing strategies to remove the surface shell with a view to achieving efficient charge transfer in CQD solids. As a result, we develop resurfacing protocols, tailored to each dot synthesis, that produce balanced In-to-As stoichiometry regardless of synthetic input, enabling us to fabricate NIR photodetectors that achieve best-in-class EQEs at 940 nm excitons (25-28%, biased), independent of the synthetic pathway.
Fast Near-Infrared Photodetection Using III-V Colloidal Quantum Dots
(Wiley, 2022-08-18) Sun, Bin; Najarian, Amin Morteza; Sagar, Laxmi Kishore; Biondi, Margherita; Choi, Min-Jae; Li, Xiyan; Levina, Larissa; Baek, Se-Woong; Zheng, Chao; Lee, Seungjin; Kirmani, Ahmad R; Sabatini, Randy; Abed, Jehad; Liu, Mengxia; Vafaie, Maral; Li, Peicheng; Richter, Lee J; Voznyy, Oleksandr; Chekini, Mahshid; Lu, Zheng-Hong; García de Arquer, F Pelayo; Sargent, Edward H
Colloidal quantum dots (CQDs) are promising materials for infrared (IR) light detection due to their tunable bandgap and their solution processing; however, to date, the time response of CQD IR photodiodes is inferior to that provided by Si and InGaAs. It is reasoned that the high permittivity of II-VI CQDs leads to slow charge extraction due to screening and capacitance, whereas III-Vs-if their surface chemistry can be mastered-offer a low permittivity and thus increase potential for high-speed operation. In initial studies, it is found that the covalent character in indium arsenide (InAs) leads to imbalanced charge transport, the result of unpassivated surfaces, and uncontrolled heavy doping. Surface management using amphoteric ligand coordination is reported, and it is found that the approach addresses simultaneously the In and As surface dangling bonds. The new InAs CQD solids combine high mobility (0.04 cm2 V-1 s-1 ) with a 4× reduction in permittivity compared to PbS CQDs. The resulting photodiodes achieve a response time faster than 2 ns-the fastest photodiode among previously reported CQD photodiodes-combined with an external quantum efficiency (EQE) of 30% at 940 nm.
Improved charge extraction in inverted perovskite solar cells with dual-site-binding ligands
(AAAS, 2024-04-12) Chen, Hao; Liu, Cheng; Xu, Jian; Maxwell, Aidan; Zhou, Wei; Yang, Yi; Zhou, Qilin; Bati, Abdulaziz S R; Wan, Haoyue; Wang, Zaiwei; Zeng, Lewei; Wang, Junke; Serles, Peter; Liu, Yuan; Teale, Sam; Liu, Yanjiang; Saidaminov, Makhsud I; Li, Muzhi; Rolston, Nicholas; Hoogland, Sjoerd; Filleter, Tobin; Kanatzidis, Mercouri G; Chen, Bin; Ning, Zhijun; Sargent, Edward H
Inverted (pin) perovskite solar cells (PSCs) afford improved operating stability in comparison to their nip counterparts but have lagged in power conversion efficiency (PCE). The energetic losses responsible for this PCE deficit in pin PSCs occur primarily at the interfaces between the perovskite and the charge-transport layers. Additive and surface treatments that use passivating ligands usually bind to a single active binding site: This dense packing of electrically resistive passivants perpendicular to the surface may limit the fill factor in pin PSCs. We identified ligands that bind two neighboring lead(II) ion (Pb2+) defect sites in a planar ligand orientation on the perovskite. We fabricated pin PSCs and report a certified quasi-steady state PCE of 26.15 and 24.74% for 0.05- and 1.04-square centimeter illuminated areas, respectively. The devices retain 95% of their initial PCE after 1200 hours of continuous 1 sun maximum power point operation at 65°C.
Efficient ethylene electrosynthesis through C–O cleavage promoted by water dissociation
(Springer Nature, 2024-06-20) Liang, Yongxiang; Li, Feng; Miao, Rui Kai; Hu, Sunpei; Ni, Weiyan; Zhang, Shuzhen; Liu, Yanjiang; Bai, Yang; Wan, Haoyue; Ou, Pengfei; Li, Xiao-Yan; Wang, Ning; Park, Sungjin; Li, Fengwang; Zeng, Jie; Sinton, David; Sargent, Edward H.
Electrochemical reduction of carbon monoxide is a promising carbonate-free approach to produce ethylene using renewable electricity. However, the performance of this process suffers from low selectivity and energy efficiency. A priority has been to weaken water dissociation with the aim of inhibiting the competing hydrogen evolution reaction but when this path was examined by replacing H2O with D2O, a further-reduced selectivity toward ethylene was observed. Here we examine approaches to promote water adsorption and to decrease the energy barrier to the ensuing water dissociation step, which could promote C–O cleavage in *CHCOH hydrogenation to *CCH. We modified a copper catalyst with the strong electron acceptor 7,7,8,8-tetracyanoquinodimethane, which made the catalyst surface electron deficient. The observed ethylene Faradaic efficiency was 75%, 1.3 times greater than that of unmodified copper control catalysts. A full-cell energy efficiency of 32% was achieved for a total projected energy cost of 154 GJ t−1 in ethylene electrosynthesis in a membrane electrode assembly.
Efficient CO and acrolein co-production via paired electrolysis
(Springer Nature, 2024-07) Wang, Xue; Li, Peihao; Tam, Jason; Howe, Jane Y.; O’Brien, Colin P.; Sedighian Rasouli, Armin; Miao, Rui Kai; Liu, Yuan; Ozden, Adnan; Xie, Ke; Wu, Jinhong; Sinton, David; Sargent, Edward H.
Paired electrolysis—the combination of a productive cathodic reaction, such as CO2 electroreduction (CO2RR), with selective oxidation on the anode—provides an electrified reaction with maximized atom and energy efficiencies. Unfortunately, direct electro-oxidation reactions typically exhibit limited Faradaic efficiencies (FEs) towards a single product. Here we apply paired electrolysis for acidic CO2RR and the model organic oxidation allyl alcohol oxidation reaction to acrolein. This CO2RR alcohol oxidation reaction system shows (96 ± 1)% FE of CO2 to CO on the cathode and (85 ± 1)% FE of allyl alcohol to acrolein on the anode. As a result of this pairing with organic oxidation on the anode, the full-cell voltage of the system is lowered by 0.7 V compared with the state-of-art acidic CO2-to-CO studies at the same 100 mA cm−2 current density. The acidic cathode avoids carbonate formation and enables a single-pass utilization of CO2 of 84% with a 6× improvement in the atom efficiency of CO2 utilization. Energy consumption analysis suggests that, when producing the same amount of CO, the system reduces energy consumption by an estimated 1.6× compared with the most energy-efficient prior acidic CO2-to-CO ambient-temperature electrolysis systems. The work suggests that paired electrolysis could be a decarbonization technology to contribute to a sustainable future
Progress and roadmap for electro-privileged transformations of bio-derived molecules
(Nature Research, 2024-04) Tian, Cong; Dorakhan, Roham; Wicks, Joshua; Chen, Zhu; Choi, Kyoung-Shin; Singh, Nirala; Schaidle, Joshua A.; Holewinski, Adam; Vojvodic, Aleksandra; Vlachos, Dionisios G.; Broadbelt, Linda J.; Sargent, Edward H.
Biomass incorporates carbon captured from the atmosphere and can serve as a renewable feedstock for producing valuable chemicals and fuels. Here we look at how electrochemical approaches can impact biomass valorization, focusing on identifying chemical transformations that lever renewable electricity and feedstocks to produce valorized products via electro-privileged transformations. First, we recommend that the field explore widening the spectrum of platform chemicals derived from bio-feedstocks, thus offering pathways to molecules that have historically been derived from petroleum. Second, we identify opportunities in electrocatalytic production of energy-dense fuels from biomass that utilize water as the hydrogen source and renewable electricity as the driving force. Finally, we look at the potential in electrochemical depolymerization to preserve key functional groups in raw feedstocks that would otherwise be lost during harsh pre-treatments in traditional depolymerization routes. Based on these priorities, we suggest a roadmap for the integration of biomass and electrochemistry and we offer milestones required to tap further into the potential of electrochemical biomass valorization.
Nickel Oxide Hole Injection Layers for Balanced Charge Injection in Quantum Dot Light-Emitting Diodes
(Wiley, 2024-04-10) Wan, Haoyue; Jung, Eui Dae; Zhu, Tong; Park, So Min; Pina, Joao M; Xia, Pan; Bertens, Koen; Wang, Ya-Kun; Atan, Ozan; Chen, Haijie; Hou, Yi; Lee, Seungjin; Won, Yu-Ho; Kim, Kwang-Hee; Hoogland, Sjoerd; Sargent, Edward H
Quantum dot (QD) light-emitting diodes (QLEDs) are promising for next-generation displays, but suffer from carrier imbalance arising from lower hole injection compared to electron injection. A defect engineering strategy is reported to tackle transport limitations in nickel oxide-based inorganic hole-injection layers (HILs) and find that hole injection is able to enhance in high-performance InP QLEDs using the newly designed material. Through optoelectronic simulations, how the electronic properties of NiOx affect hole injection efficiency into an InP QD layer, finding that efficient hole injection depends on lowering the hole injection barrier and enhancing the acceptor density of NiOx is explored. Li doping and oxygen enriching are identified as effective strategies to control intrinsic and extrinsic defects in NiOx, thereby increasing acceptor density, as evidenced by density functional theory calculations and experimental validation. With fine-tuned inorganic HIL, InP QLEDs exhibit a luminance of 45 200 cd m-2 and an external quantum efficiency of 19.9%, surpassing previous inorganic HIL-based QLEDs. This study provides a path to designing inorganic materials for more efficient and sustainable lighting and display technologies.
All-Perovskite Tandems Enabled by Surface Anchoring of Long-Chain Amphiphilic Ligands
(ACS, 2024-02-09) Maxwell, Aidan; Chen, Hao; Grater, Luke; Li, Chongwen; Teale, Sam; Wang, Junke; Zeng, Lewei; Wang, Zaiwei; Park, So Min; Vafaie, Maral; Sidhik, Siraj; Metcalf, Isaac W.; Liu, Yanjiang; Mohite, Aditya D.; Chen, Bin; Sargent, Edward H.
Perovskite solar cells (PSCs) in the pin structure are limited by nonradiative recombination at the electron transport layer (ETL) interface, which is exacerbated in narrow-bandgap (∼1.2 eV) Pb–Sn PSCs due to surface Sn oxidation and detrimental p-doping. Photoluminescence quantum yield studies herein indicated that ethane-1,2-diammonium (EDA) passivation only partially alleviates perovskite/ETL energetic losses. We pursued passivation of the defect-rich perovskite:ETL interface to reduce nonradiative losses; our target was to combine chemical coordination of Sn sites with the introduction of an interlayer, which we implemented by introducing long-chain carboxylic acid ligands at the perovskite surface. Treatment with oleic acid (OA) led to reduced recombination at the perovskite/ETL interface and evidence of Sn2+ coordination. This reduced the VOC deficit of Pb–Sn PSCs to 0.34 V, resulting in a 0.89 V VOC and PCE of 23.0% (22.4% stabilized). Incorporating the OA-treated Pb–Sn layer into a monolithic all-perovskite tandem, we report a 27.3% PCE (26.4% certified) and a VOC of 2.21 V.
Dicarboxylic Acid-Assisted Surface Oxide Removal and Passivation of Indium Antimonide Colloidal Quantum Dots for Short-Wave Infrared Photodetectors
(Wiley, 2024-02-19) Zhang, Yangning; Xia, Pan; Rehl, Benjamin; Parmar, Darshan H; Choi, Dongsun; Imran, Muhammad; Chen, Yiqing; Liu, Yanjiang; Vafaie, Maral; Li, Chongwen; Atan, Ozan; Pina, Joao M; Paritmongkol, Watcharaphol; Levina, Larissa; Voznyy, Oleksandr; Hoogland, Sjoerd; Sargent, Edward H
Heavy-metal-free III-V colloidal quantum dots (CQDs) are promising materials for solution-processed short-wave infrared (SWIR) photodetectors. Recent progress in the synthesis of indium antimonide (InSb) CQDs with sizes smaller than the Bohr exciton radius enables quantum-size effect tuning of the band gap. However, it has been challenging to achieve uniform InSb CQDs with band gaps below 0.9 eV, as well as to control the surface chemistry of these large-diameter CQDs. This has, to date, limited the development of InSb CQD photodetectors that are sensitive to ≥${\ge }$ 1400 nm light. Here we adopt solvent engineering to facilitate a diffusion-limited growth regime, leading to uniform CQDs with a band gap of 0.89 eV. We then develop a CQD surface reconstruction strategy that employs a dicarboxylic acid to selectively remove the native In/Sb oxides, and enables a carboxylate-halide co-passivation with the subsequent halide ligand exchange. We find that this strategy reduces trap density by half compared to controls, and enables electronic coupling among CQDs. Photodetectors made using the tailored CQDs achieve an external quantum efficiency of 25 % at 1400 nm, the highest among III-V CQD photodetectors in this spectral region.
Low-loss contacts on textured substrates for inverted perovskite solar cells
(Nature Research, 2023-10-23) Park, So Min; Wei, Mingyang; Lempesis, Nikolaos; Yu, Wenjin; Hossain, Tareq; Agosta, Lorenzo; Carnevali, Virginia; Atapattu, Harindi R; Serles, Peter; Eickemeyer, Felix T; Shin, Heejong; Vafaie, Maral; Choi, Deokjae; Darabi, Kasra; Jung, Eui Dae; Yang, Yi; Kim, Da Bin; Zakeeruddin, Shaik M; Chen, Bin; Amassian, Aram; Filleter, Tobin; Kanatzidis, Mercouri G; Graham, Kenneth R; Xiao, Lixin; Rothlisberger, Ursula; Grätzel, Michael; Sargent, Edward H
Inverted perovskite solar cells (PSCs) promise enhanced operating stability compared to their normal-structure counterparts1-3. To improve efficiency further, it is crucial to combine effective light management with low interfacial losses4,5. Here we develop a conformal self-assembled monolayer (SAM) as the hole-selective contact on light-managing textured substrates. Molecular dynamics simulations indicate that cluster formation during phosphonic acid adsorption leads to incomplete SAM coverage. We devise a co-adsorbent strategy that disassembles high-order clusters, thus homogenizing the distribution of phosphonic acid molecules, and thereby minimizing interfacial recombination and improving electronic structures. We report a laboratory-measured power conversion efficiency (PCE) of 25.3% and a certified quasi-steady-state PCE of 24.8% for inverted PSCs, with a photocurrent approaching 95% of the Shockley-Queisser maximum. An encapsulated device having a PCE of 24.6% at room temperature retains 95% of its peak performance when stressed at 65 °C and 50% relative humidity following more than 1,000 h of maximum power point tracking under 1 sun illumination. This represents one of the most stable PSCs subjected to accelerated ageing: achieved with a PCE surpassing 24%. The engineering of phosphonic acid adsorption on textured substrates offers a promising avenue for efficient and stable PSCs. It is also anticipated to benefit other optoelectronic devices that require light management.
Selective Electrified Propylene-to-Propylene Glycol Oxidation on Activated Rh-Doped Pd
(American Chemical Society, 2024-03-27) Huang, Jianan Erick; Chen, Yiqing; Ou, Pengfei; Ding, Xueda; Yan, Yu; Dorakhan, Roham; Lum, Yanwei; Li, Xiao-Yan; Bai, Yang; Wu, Chengqian; Fan, Mengyang; Lee, Mi Gyoung; Miao, Rui Kai; Liu, Yanjiang; O'Brien, Colin; Zhang, Jinqiang; Tian, Cong; Liang, Yongxiang; Xu, Yi; Luo, Mingchuan; Sinton, David; Sargent, Edward H
Renewable-energy-powered electrosynthesis has the potential to contribute to decarbonizing the production of propylene glycol, a chemical that is used currently in the manufacture of polyesters and antifreeze and has a high carbon intensity. Unfortunately, to date, the electrooxidation of propylene under ambient conditions has suffered from a wide product distribution, leading to a low faradic efficiency toward the desired propylene glycol. We undertook mechanistic investigations and found that the reconstruction of Pd to PdO occurs, followed by hydroxide formation under anodic bias. The formation of this metastable hydroxide layer arrests the progressive dissolution of Pd in a locally acidic environment, increases the activity, and steers the reaction pathway toward propylene glycol. Rh-doped Pd further improves propylene glycol selectivity. Density functional theory (DFT) suggests that the Rh dopant lowers the energy associated with the production of the final intermediate in propylene glycol formation and renders the desorption step spontaneous, a concept consistent with experimental studies. We report a 75% faradic efficiency toward propylene glycol maintained over 100 h of operation.
Transient Measurements and Simulations Correlate Exchange Ligand Concentration and Trap States in Colloidal Quantum Dot Photodetectors
(ACS, 2023-12-27) Parmar, Darshan H; Rehl, Benjamin; Atan, Ozan; Hoogland, Sjoerd; Sargent, Edward H
Colloidal quantum dot (CQD) photodetectors (PDs) can detect wavelengths longer than the 1100 nm limit of silicon because of their highly tunable bandgaps. CQD PDs are acutely affected by the ligands that separate adjacent dots in a CQD-solid. Optimizing the exchange solution ligand concentration in the processing steps is crucial to achieving high photodetector performance. However, the complex mix of chemistry and optoelectronics involved in CQD PDs means that the effects of the exchange solution ligand concentration on device physics are poorly understood. Here we report direct correspondence between simulated and experimental transient photocurrent responses in CQD PDs. For both deficient and excess conditions, our model demonstrated the experimental changes to the transient photocurrent aligned with changes in trap state density. Combining transient photoluminescence, absorption, and photocurrent with this simulation model, we revealed that different mechanisms are responsible for the increased trap density induced by excess and deficient active layer ligand concentrations.
Ligand-modified nanoparticle surfaces influence CO electroreduction selectivity
(Nature Research, 2024-04-06) Shirzadi, Erfan; Jin, Qiu; Zeraati, Ali Shayesteh; Dorakhan, Roham; Goncalves, Tiago J; Abed, Jehad; Lee, Byoung-Hoon; Rasouli, Armin Sedighian; Wicks, Joshua; Zhang, Jinqiang; Ou, Pengfei; Boureau, Victor; Park, Sungjin; Ni, Weiyan; Lee, Geonhui; Tian, Cong; Meira, Debora Motta; Sinton, David; Siahrostami, Samira; Sargent, Edward H
Improving the kinetics and selectivity of CO2/CO electroreduction to valuable multi-carbon products is a challenge for science and is a requirement for practical relevance. Here we develop a thiol-modified surface ligand strategy that promotes electrochemical CO-to-acetate. We explore a picture wherein nucleophilic interaction between the lone pairs of sulfur and the empty orbitals of reaction intermediates contributes to making the acetate pathway more energetically accessible. Density functional theory calculations and Raman spectroscopy suggest a mechanism where the nucleophilic interaction increases the sp2 hybridization of CO(ad), facilitating the rate-determining step, CO* to (CHO)*. We find that the ligands stabilize the (HOOC-CH2)* intermediate, a key intermediate in the acetate pathway. In-situ Raman spectroscopy shows shifts in C-O, Cu-C, and C-S vibrational frequencies that agree with a picture of surface ligand-intermediate interactions. A Faradaic efficiency of 70% is obtained on optimized thiol-capped Cu catalysts, with onset potentials 100 mV lower than in the case of reference Cu catalysts.
Bimolecularly passivated interface enables efficient and stable inverted perovskite solar cells
(American Association for the Advancement of Science, 2023-11-17) Liu, Cheng; Yang, Yi; Chen, Hao; Xu, Jian; Liu, Ao; Bati, Abdulaziz S R; Zhu, Huihui; Grater, Luke; Hadke, Shreyash Sudhakar; Huang, Chuying; Sangwan, Vinod K; Cai, Tong; Shin, Donghoon; Chen, Lin X; Hersam, Mark C; Mirkin, Chad A; Chen, Bin; Kanatzidis, Mercouri G; Sargent, Edward H
Compared with the n-i-p structure, inverted (p-i-n) perovskite solar cells (PSCs) promise increased operating stability, but these photovoltaic cells often exhibit lower power conversion efficiencies (PCEs) because of nonradiative recombination losses, particularly at the perovskite/C60 interface. We passivated surface defects and enabled reflection of minority carriers from the interface into the bulk using two types of functional molecules. We used sulfur-modified methylthio molecules to passivate surface defects and suppress recombination through strong coordination and hydrogen bonding, along with diammonium molecules to repel minority carriers and reduce contact-induced interface recombination achieved through field-effect passivation. This approach led to a fivefold longer carrier lifetime and one-third the photoluminescence quantum yield loss and enabled a certified quasi-steady-state PCE of 25.1% for inverted PSCs with stable operation at 65°C for >2000 hours in ambient air. We also fabricated monolithic all-perovskite tandem solar cells with 28.1% PCE.
Anion optimization for bifunctional surface passivation in perovskite solar cells
(Nature Research, 2023-12) Xu, Jian; Chen, Hao; Grater, Luke; Liu, Cheng; Yang, Yi; Teale, Sam; Maxwell, Aidan; Mahesh, Suhas; Wan, Haoyue; Chang, Yuxin; Chen, Bin; Rehl, Benjamin; Park, So Min; Kanatzidis, Mercouri G; Sargent, Edward H
Pseudo-halide (PH) anion engineering has emerged as a surface passivation strategy of interest for perovskite-based optoelectronics; but until now, PH anions have led to insufficient defect passivation and thus to undesired deep impurity states. The size of the chemical space of PH anions (>106 molecules) has so far limited attempts to explore the full family of candidate molecules. We created a machine learning workflow to speed up the discovery process using full-density functional theory calculations for training the model. The physics-informed machine learning model allowed us to pinpoint promising molecules with a head group that prevents lattice distortion and anti-site defect formation, and a tail group optimized for strong attachment to the surface. We identified 15 potential bifunctional PH anions with the ability to passivate both donors and acceptors, and through experimentation, discovered that sodium thioglycolate was the most effective passivant. This strategy resulted in a power-conversion efficiency of 24.56% with a high open-circuit voltage of 1.19 volts (24.04% National Renewable Energy Lab-certified quasi-steady-state) in inverted perovskite solar cells. Encapsulated devices maintained 96% of their initial power-conversion energy during 900 hours of one-sun operation at the maximum power point.
A thermotropic liquid crystal enables efficient and stable perovskite solar modules
(Nature Research, 2024-03) Yang, Yi; Liu, Cheng; Ding, Yong; Ding, Bin; Xu, Jian; Liu, Ao; Yu, Jiaqi; Grater, Luke; Zhu, Huihui; Hadke, Shreyash Sudhakar; Sangwan, Vinod K.; Bati, Abdulaziz S. R.; Hu, Xiaobing; Li, Jiantao; Park, So Min; Hersam, Mark C.; Chen, Bin; Nazeeruddin, Mohammad Khaja; Kanatzidis, Mercouri G.; Sargent, Edward H.
Perovskite solar cells have seen impressive progress in performance and stability, yet maintaining efficiency while scaling area remains a challenge. Here we find that additives commonly used to passivate large-area perovskite films often co-precipitate during perovskite crystallization and aggregate at interfaces, contributing to defects and to spatial inhomogeneity. We develop design criteria for additives to prevent their evaporative precipitation and enable uniform passivation of defects. We explored liquid crystals with melting point below the perovskite processing temperature, functionalization for defect passivation and hydrophobicity to improve device stability. We find that thermotropic liquid crystals such as 3,4,5-trifluoro-4′-(trans-4-propylcyclohexyl)biphenyl enable large-area perovskite films that are uniform, low in defects and stable against environmental stress factors. We demonstrate modules with a certified stabilized efficiency of 21.1% at an aperture area of 31 cm2 and enhanced stability under damp-heat conditions (ISOS-D-3, 85% relative humidity, 85 °C) with T86 (the duration for the efficiency to decay to 86% of the initial value) of 1,200 h, and reverse bias with (ISOS-V-1, negative maximum-power-point voltage) and without bypass diodes.
Catalyst design for electrochemical CO2 reduction to ethylene
(Cell Press, 2024-01-03) Chen, Yuanjun; Miao, Rui Kai; Yu, Christine; Sinton, David; Xie, Ke; Sargent, Edward H.
In CO2 electrochemical (CO2R) production of chemicals and fuels, it is a long-standing challenge to suppress the competing hydrogen evolution reaction (HER) and steer selectivity to a single valuable product. Ethylene is a desired model molecule in light of its large market size, range of applications from polymers to sustainable aviation fuel, and large present-day carbon intensity. The reaction pathways and reactivity of CO2R rely on catalyst surface properties and local reaction environments. Here we review the mechanistic understanding of CO2R to ethylene; we then discuss catalyst design strategies in light of the link between catalyst structure, reaction pathways, and ethylene production performance. We close with challenges in catalyst design and provide an outlook for further research directions to accelerate the rational design of catalysts.
Site-selective protonation enables efficient carbon monoxide electroreduction to acetate
(2024-01) Wang, Xinyue; Chen, Yuanjun; Li, Feng; Miao, Rui Kai; Huang, Jianan Erick; Zhao, Zilin; Li, Xiao-Yan; Dorakhan, Roham; Chu, Senlin; Wu, Jinhong; Zheng, Sixing; Ni, Weiyan; Kim, Dongha; Park, Sungjin; Liang, Yongxiang; Ozden, Adnan; Ou, Pengfei; Hou, Yang; Sinton, David; Sargent, Edward H
Electrosynthesis of acetate from CO offers the prospect of a low-carbon-intensity route to this valuable chemical--but only once sufficient selectivity, reaction rate and stability are realized. It is a high priority to achieve the protonation of the relevant intermediates in a controlled fashion, and to achieve this while suppressing the competing hydrogen evolution reaction (HER) and while steering multicarbon (C2+) products to a single valuable product--an example of which is acetate. Here we report interface engineering to achieve solid/liquid/gas triple-phase interface regulation, and we find that it leads to site-selective protonation of intermediates and the preferential stabilization of the ketene intermediates: this, we find, leads to improved selectivity and energy efficiency toward acetate. Once we further tune the catalyst composition and also optimize for interfacial water management, we achieve a cadmium-copper catalyst that shows an acetate Faradaic efficiency (FE) of 75% with ultralow HER (<0.2% H2 FE) at 150 mA cm-2. We develop a high-pressure membrane electrode assembly system to increase CO coverage by controlling gas reactant distribution and achieve 86% acetate FE simultaneous with an acetate full-cell energy efficiency (EE) of 32%, the highest energy efficiency reported in direct acetate electrosynthesis.

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