Perovskite solar cell series
1. Nature: Stable inverted perovskite cells!
Compared with normal structure solar cells (PSC), inverted perovskite solar cells (PSC) are expected to have enhanced operational stability. To further improve efficiency, it is crucial to combine efficient light management with low interface losses. Michael Grätzel of the Ecole Polytechnique Fédérale de Lausanne in Switzerland, Edward H. Sargent of Northwestern University in the United States, and the University of Toronto in Canada developed a conformal self-assembled monolayer (SAM) as a hole-selective contact on a light-managed textured substrate. Molecular dynamics simulations indicate that cluster formation during phosphonic acid adsorption results in incomplete SAM coverage.
A co-adsorbent strategy was designed to break up higher-order clusters to homogenize the distribution of phosphonic acid molecules, thereby minimizing interfacial reorganization and improving the electronic structure. The inverted PSC has a laboratory-measured power conversion efficiency (PCE ) of 25.3%, a certified quasi-steady-state PCE of 24.8%, and a photocurrent close to 95% of the Shockley-Queisser maximum. A packaged device with a PCE of 4.6% at room temperature maintained 95% of peak performance when stressed at 65°C and 50% relative humidity after more than 1000 hours of maximum power point tracking under 1 sun. This is one of the most stable PSCs subjected to accelerated aging ( PCE exceeding 24% ).
Original link: https://www.nature.com/articles/s41586-023-06745-7
2. Nature: Intermolecular homogeneous bonding induces octahedral structure germanium perovskite
Perovskites with low ionic radius metal centers (such as Ge perovskites) do not form octahedral [GeI 6 ] perovskites but crystallize into poles due to geometric constraints and electron energy gain obtained through distortion. non-perovskite structure. Inspired by the principles of supramolecular synthesis, Edward H. Sargent of the University of Toronto and others reported a method of assembling organic scaffolds in the perovskite structure to affect the geometric arrangement and electronic configuration of the crystal, thereby suppressing the isolated electron concentration of Ge and forming symmetry. octahedral structure.
In order to generate extended homogeneous noncovalent bonding, organic motifs need to have self-complementary properties utilizing different donor and acceptor sites. Compared with the non-perovskite structure, the obtained [GeI 6 ] 4- octahedron has a significant red-shifted direct band gap (experimental measurement value is greater than 0.5 eV ) and smaller octahedral distortion (according to measured single crystal X -ray diffraction extrapolated from the data), and higher electron and hole mobilities (estimated by density functional theory). This design principle is not limited to 2D Ge perovskites, but also implements it in the case of copper perovskites (also low-radius metal centers) and extends it to quasi-2D systems. The authors report that Ge perovskite photodiodes outperform non-octahedral and lead analogues. Building secondary sublattices intertwined with inorganic frameworks within the crystal provides a new synthetic tool for preparing hybrid lattices with controlled twist and orbital alignment, overcoming the limitations of traditional perovskites.
Original link: https://www.nature.com/articles/s41586-023-06209-y
3. Nature: 24.3% all-perovskite triple-junction solar cell
Perovskites' tunable band gaps and simple fabrication make them attractive for multijunction photovoltaics. However, light-induced phase segregation limits their efficiency and stability: this occurs in wide-bandgap (>1.65 eV) iodide/bromide hybrid perovskite absorbers.
This research aims to solve the phase separation problem in perovskite solar cells, especially in the top sub-cell of triple-junction perovskite solar cells. Edward H. Sargent of the University of Toronto and others used rubidium/cesium mixed cationic inorganic perovskite as the absorber layer of the top sub-cell to create an all-perovskite triple-junction solar cell and achieved an efficiency of 24.3% (23.29% quasi-stable state efficiency), which is the first reported certified efficiency of a perovskite-based triple-junction solar cell. This three-cell stacked battery can still maintain 80% of its initial efficiency after 420 hours of operation at the maximum power point.
Original link: https://www.nature.com/articles/s41586-023-06209-y
4. Nature: Surface potential adjustment increases series voltage of all-perovskite cells
In perovskite solar cells, wide bandgap (more than 1.7 electron volts) cells have a greater open circuit voltage ( V OC ) deficit than perovskite cells of about 1.5 electron volts. Quasi-Fermi level splitting measurements show that the limit VThe recombination of OC occurs at the electron transport layer contact. This results from uneven surface potential and poor energy alignment of the perovskite-electron transport layer.
Common monoammonium surface treatments cannot solve this problem; as an alternative, Edward H. Sargent of the University of Toronto & Yanfa Yan of the University of Toledo introduced diammonium molecules to improve the perovskite surface state and achieve a more uniform spatial distribution of the surface potential. . Using 1,3-propanediammonium, the quasi-Fermi level splitting was increased by 90mV, resulting in a 1.79 eV perovskite solar cell with a certified VOC of 1.33 eV and a photoelectric conversion efficiency (PCE) of over 19%. Incorporating this layer into a monolithic all-perovskite tandem cell resulted in a record VOC of 2.19 eV ( 89% of the detailed equilibrium VOC limit) and a PCE of over 27% (26.3% certified quasi-steady state). These tandem cells maintained more than 86% of their initial PCE after 500 hours of operation.
Original link: https://www.nature.com/articles/s41586-022-05541-z
5. Scienc e: Systematic study of ammonium ligands in perovskites
Perovskite solar cells (PSCs) have achieved rapid progress in performance and stability due to interfacial two- and three-dimensional heterostructures containing ammonium ion intercalation. However, as the field strives for higher durability, additional tools are needed to avoid progressive ligand intercalation to minimize degradation at high temperatures.
The team of Kenneth R. Graham, Michael Grätzel and Edward H. Sargent used ammonium ions that do not react with bulk perovskites and systematically studied a library of different ligand molecular structures. The study found that fluorinated aniline provided an interface passivation effect while minimizing reactivity with the perovskite. The certified quasi-steady-state power conversion efficiency of inverted structure PSCs based on this method is 24.09%. In the case of device packaging, the maximum power point T 85 life span reaches 1560 hours under 1 solar radiation (85°C and 50% relative humidity) .
Original link: https://www.science.org/doi/10.1126/science.adi4107
6. Science: Ligand engineering helps perovskite solar cells operate at high temperatures
Perovskite solar cells (PSCs), composed of interfacial two- and three-dimensional heterostructures containing ammonium ligands embedded, have enabled rapid progress toward the goal of combining performance and stability. However, as the field continues to seek greater durability, additional tools are needed to avoid progressive ligand intercalation to minimize degradation at high temperatures.
Kenneth R. Graham of the University of Kentucky, Michael Grätzel of the Polytechnic Institute of Lausanne in Switzerland, Edward H. Sargent of the University of Toronto and others used ammonium ligands that do not react with most perovskites and studied libraries that systematically changed the molecular structure of the ligands. Fluorinated aniline was found to provide interfacial passivation while minimizing reactivity with the perovskite. Using this approach, we report a certified quasi-steady-state power conversion efficiency of 24.09% for the inverted structure PSC. The maximum power point of the T85 under 1 sun illumination was recorded for 1560 hours in a packaged device operating at 85°C and 50% relative humidity.
Original link: https://www.science.org/doi/10.1126/science.adi4107
7. Science: Bimolecular passivation interface enables efficient and stable inverted perovskite solar cells
Inverted (pin) perovskite solar cells (PSCs) are expected to improve operational stability compared to nip structures, but these photovoltaic cells generally exhibit lower power conversion efficiencies (PCE) due to non-radiative recombination losses, especially in Perovskite/C60 interface.
Bin Chen, Mercouri G. Kanatzidis & Edward H. Sargent of the University of Toronto passivated surface defectsby using two types of functional molecules . Sulfur-modified methyl sulfide molecules are used to passivate surface defects and inhibit recombination through strong coordination and hydrogen bonding, and diammonium molecules are used to repel minority carriers and reduce contact-induced interfacial recombination through field effect passivation. This approach extends carrier lifetime fivefold, reduces photoluminescence quantum yield loss by one-third, and enables certified quasi-steady-state PCE of inverted PSCs of 25.1% at 65°C in ambient air Stable operation >2000 hours. A monolithic all-perovskite tandem solar cell with a PCE of 28.1% was also fabricated.
Original link: https://www.science.org/doi/10.1126/science.adk1633
8. Science: Lewis base molecular design improves stability and efficiency of inverted perovskite solar cells
Lewis base molecules incorporating uncoordinated 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 energies among members of the library of Lewis base molecules studied here.
Through experiments, Edward H. Sargent of the University of Toronto & Yanfa Yan of the University of Toledo discovered that the best inverted PSCs were treated with 1,3-bis(diphenylphosphine)propane (DPPP), a passivating, binding and bridging interface. and GB's diphosphine Lewis base maintained a power conversion efficiency (PCE) slightly higher than its initial PCE of ~23% after >3500 hours of continuous operation at the maximum power point and ~40°C under simulated AM1.5 illumination. . DPPP-treated devices also showed a similar increase in PCE after >1500 hours at 85°C open circuit conditions.
Original link: https://www.science.org/doi/10.1126/science.ade3970
9. Nat. Energy: 3.33 V! Triple- junction all-perovskite solar cells
Monolithic all-perovskite triple-junction solar cells have power conversion efficiencies that exceed those of double-junction tandem solar cells and far exceed the equilibrium limit of single-junction solar cells. However, their performance is limited by large deficiencies in open-circuit voltage and short-circuit current density in wide-bandgap perovskite subcells.
Edward H. Sargent of the University of Toronto , René AJ Janssen of Eindhoven University of Technology and others found that halide homogenization achieves low energy loss in perovskites and improves efficiency in all-perovskite solar cells. found that the diammonium halide salt, propane -1,3- diammonium iodide, introduced during the film fabrication process improved halide homogenization in the Br -rich perovskite, resulting in improved operational stability and a record of 1.44 The open circuit voltage record of V.
The efficient wide-gap subcell enables the fabrication of monolithic all-perovskite triple-junction solar cells with an open-circuit voltage of 3.33 V and achieves a PCE of 25.1% . Overall, this work demonstrates the huge application potential of all-perovskite triple-junction solar cells .
Original link: https://www.nature.com/articles/s41586-023-06006-7
10. Nature Materials: Bifunctional pH anionic sodium thioglycolate
Pseudohalide (PH) anion engineering has become an interesting surface passivation strategy in perovskite-based optoelectronics; but so far, pH anions have resulted in insufficient defect passivation, resulting in undesirable deep impurity states. The size of the pH anion chemical space (>106 molecules) has thus far limited attempts to explore the entire family of candidate molecules.
Edward H. Sargent of the University of Toronto, Canada, and Northwestern University in the United States created a machine learning workflow that uses full density functional theory calculations to train models to speed up the discovery process. Physics-based machine learning models allow us to pinpoint promising molecules with head groups that prevent lattice distortion and anti-site defect formation and tail groups optimized for strong attachment to surfaces.
The researchers identified 15 potential bifunctional pH anions capable of passivating both donors and acceptors, and experimentally found sodium thioglycolate to be the most effective passivator. This strategy enables the inverted perovskite solar cell to achieve a power conversion efficiency of 24.56% and an open-circuit voltage as high as 1.19 V (the National Renewable Energy Laboratory-certified quasi-steady-state voltage is 24.04%). The packaged device maintained an initial photoelectric conversion efficiency of 96% during one daily operation of 900 hours at the maximum power point.
Original link: https://www.nature.com/articles/s41563-023-01705-y
11. Nano Letters: Quantum dot infrared photodetector
Solution-processed colloidal quantum dots (CQDs) are ideal materials for photodetectors operating in the shortwave infrared region (SWIR). Research by Edward H. Sargent of the University of Toronto and others found that commonly used hole transport layer (HTL) materials exhibit low carrier mobility, limiting the response speed of photodiodes.
Therefore, the authors developed a reverse (pin) SWIR photodetector that can operate at 1370 nm, which uses NiOx as HTL, ultimately shortening the photodiode fall times by 4 times (EDT is ~800 ns, NiOx is ~200 ns ). Optoelectronic simulations show that the high carrier mobility of NiOx enhances the electric field in the active layer, reduces the overall transmission time, and increases the response time of the photodetector.
Original link: https://pubs.acs.org/doi/10.1021/acs.nanolett.3c00491
12. JACS: Bifunctional electron transport agents for red colloidal quantum dot light-emitting diodes
Indium phosphide (InP) quantum dots enable light-emitting diodes (LEDs) that are heavy metal-free, have narrow emission linewidths, and are physically flexible. However, the electron transport layer (ETL) ZnO/ZnMgO in high-performance red InP/ZnSe/ZnS LEDs has a high defect density, which quenches the emission when deposited on InP and leads to performance degradation due to trap migration causing the ETL to InP emission layer.
Edward H. Sargent of the University of Toronto studied trap states in InP/ZnSe/ZnS core-shell quantum dots and identified the role of the ZnS shell, where Zn2+ vacancies are formed and S− migrates to the ETL layer. This was found to accelerate PL quenching, causing it to become more severe during photogeneration and when a bias voltage is applied.
The study hypothesized that a bifunctional reagent could address this challenge if it contained an electron-deficient backbone to ensure the required electron mobility, combined with an electron-rich unit to bind to Zn 2+ to passivate surface traps. This concept is implemented using molecules with a backbone containing triazine groups (for electron mobility) and a star structure (for bending) to achieve passivation of independent cyano groups to suppress the InP/ZnSe/ZnS cores Traps in the shell structure.
The combination of CN with uncoordinated Zn 2+ surface states enables passivation and prevents S vacancy migration and O vacancy formation. In this work, local in-situ passivation is achieved for the first time using ETL in InP LEDs, which achieves the highest EQE among organic ETL-based red InP LEDs.
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