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Research Highlight

Effect of Halogenation on the Crystallization Kinetics and Molecular Packing for High-Performance Organic Solar Cells

A series of halogenated non-fused ring electron acceptors (NFREAs) incorporating F, Cl, and Br, are synthesized to investigate the halogenation effect on the crystallization process, phase separation, molecular packing, and charge transfer. Chlorination enhances the Coulomb attractive energy to facilitate exciton dissociation. Chlorinated acceptors exhibit a longer crystallization time and a longer exciton diffusion length. Consequently, two chlorinated NFREAs, TCN-Cl, and PCN-Cl, yield an impressive power conversion efficiency (PCE) of 14.85% and 15.30%, respectively, when blended with PM6 and J52 donors. This work has been published in Advanced Functional Materials (DOI:10.1002/adfm.202311736),

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Antisolvent-Free Heterogenous Nucleation in Wide-Band CsPbI2Br Perovskite

In the article published in Small (DOI: 10.1002/smll.202307840), high quality CsPbI2Br film is achieved though antisolvent-free heterogenous nucleation by introducing a metastable Lewis acid-base adduct of PbX2-TBP. Preferential decomposition of such adducts at low temperature annealing leads to formation of perovskite seeds, followed by crystal growth assisted by PbX2-DMSO. PSCs constructed with the optimized CsPbI2Br film demonstrate a remarkable PCE of 16.5%, with an impressive VOC reaching 1.3 V.


Guided Growth Ultrathin Metal Film for Efficient Semi-Transparent Organic Solar Cells 

In the article published in Advanced Energy Materials (DOI:10.1002/aenm.202203266), a facile approach of introducing pre-located and ligand-optimized Ag nanoparticles to assist the formation of high-quality ultrathin (≈7 nm) evaporated Ag films is demonstrated for transparent top electrodes. Devices employing these films exhibit remarkable electrical and optical properties, and excellent interfacial contact with the lower layer. As prepared semi-transparent organic solar cells achieve a power conversion efficiency of 12.80% with high light utilization efficiency of 4.422%. This i s a collaboration work with Prof. Wallace Choy's team from the University of Hong Kong.

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Non-Fused Ring Acceptors Achieving over 15.6% Efficiency Organic Solar Cell

Non-fused ring electron acceptors are becoming attractive in organic solar cells due to their low cost and easy synthesis. In the article published in Advanced Energy Materials (DOI:10.1002/aenm.202203402), we demonstrate a ternary blend using two in-house designed non-fused ring electron acceptors and a polymer donor to form an alloy-like acceptor and vertical phase separation in the bulk-heterojunction.

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Organic Solar Cell With Efficiency Over 20% and Voc Exceeding 2.1 V Enabled by Tandem with All-Inorganic Perovskite 

In the article published in Advanced Science (DOI:10.1002/advs.202200445), we reported an organic solar cell with efficiency over 20% and Voc exceeding 2.1 V enabled by tandem with all-inorganic perovskite and a thermal annealing-free process which facilitates charge transport in the interconnecting layer. This work demonstrates the great potential of tandem solar cell incorporating perovskite and organic absorber.

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Dual-functional Ambipolar Non-Fused Ring Electron Acceptor as Third Component in Ternary Organic Solar Cell 

Non-fused ring electron acceptors (NFREAs) are attractive for organic solar cells (OSCs) due to their lower cost and easier synthesis step compared with fused ring type counterparts. In the article published in Nano Energy (DOI:10.1016/j.nanoen.2022.107186), we demonstrate ternary OSCs with two tailor-made NFREAs to improve the efficiency of NFREA-based OSCs. An ambipolar NFREA with dual functions of both electron accepting and donating is employed as third component in ternary blend to provide smooth multiple charge transfer routes without accumulation, and to generate additional photoexcited carriers at the two NFREAs interface.

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Localized Dion-Jacobson 2D-3D Heterojunction (L2D-3DH) for Efficient and Stable Perovskite Solar Cells

2D-3D perovskites have been demonstrated in either capping structure or interspersing structure. However, the former restricts the charge extraction due to poor charge transport across organic spacer while the latter requires strict control of vertical orientation in 2D perovskite. Therefore, in the article published in Nano Energy (DOI: 10.1016/j.nanoen.2021.106666), we introduced a novel structure of L2D-3DH, in which 2D perovskites are grown locally on the selective area of 3D perovskite without fully covering, so that the charge transport is not affected regardless of the crystal orientation. Despite a partial coverage of 2D perovskite, our L2D-3DH structure significantly improves the stability of perovskite solar cell due to stable structure of Dion-Jacobson phase 2D perovskite. 


Universal Strategy for Improving Perovskite Photodiode Performance: Interfacial Built-In Electric Field Manipulated by Unintentional Doping

In the article at Advanced Science (DOI:10.1002/advs.202101729), we provide a general design guideline for high-performance perovskite photodiodes through an interfacial electric field for efficient carrier separation and transport. The interfacial electric field can be modulated by unintentional doping of the perovskite, whose doping type and density can be controlled by the annealing time and temperature.

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Electron-Deficient Diketone Unit Engineering for Non-fused Ring Acceptors Enabling Over 13% Efficiency in Organic Solar Cells

Different from the commonly studied non-fullerene electron acceptors with large fused backbone architecture and tedious synthesis steps, non-fused ring electron acceptors (NFREAs) are attractive for organic solar cells (OSC) due to their simple synthesis and comparable device performance. In the article at Journal of Materials Chemistry A (DOI:10.1039/D1TA03643B), we employed the strategy of electron-deficient diketone unit in efficient NFREAs with noncovalent interactions for achieving high performance OSC with PCE over 13.3%.


Solution-processed AgCNT transparent electrode for Semi-transparent Organic Solar Cell

In the article at Advanced Optical Materials (DOI/10.1002/adom.202002108), the AgCNT film is employed as a top transparent electrode of semi-transparent organic solar cell (STOSC). STOSCs with solution-processed AgCNTs transparent electrode exhibit higher average visible transmittance and color rendering index than that with evaporated thin metal electrode, and comparable efficiency.

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High-Performance Quasi-2D Perovskite Solar Cells with Power Conversion Efficiency Over 20% Fabricated in Humidity-Controlled Ambient Air

In the article at Chemical Engineering Journal (DOI:10.1016/j.cej.2021.130949), we fabricated quasi-2D perovskite in a humidity-controlled ambient air employing fluorinated benzylammonium iodide as bulky cation. The corresponding perovskite solar cell yields a power conversion efficiency of 20.12% and a relatively high open-circuit voltage of 1.223 V. This work shed light on the development of high-quality quasi-2D perovskite film fabricated in humidity-controlled ambient air by simple and easy process, which is appealing for the future industrialization of PSCs with low-cost.

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Simultaneous enhancements in the Seebeck coefficient and conductivity of PEDOT:PSS by blending ferroelectric BaTiO3 nanoparticles

In the article in Journal of Materials Chemistry A (DOI:10.1039/d1ta04235a), we reported simultaneous enhancements in the Seebeck coefficient and conductivity of PEDOT:PSS by adding ferroelectric barium titanate (BaTiO3) nanoparticles. The BaTiO3 can enhance the Seebeck coefficient from 23.8 to 40.7 mVK-1. The conductivity of the continuous PEDOT:PSS phase in the composite films can be enhanced from 587 to 1552 Scm-1. The enhancement in the Seebeck coefficient is ascribed to the energy filtering of low-energy charge carriers in PEDOT:PSS due to the spontaneous electric polarization of BaTiO3, and the increase in the conductivity is attributed to the secondary doping of PEDOT:PSS related to the high dielectric constant of the BaTiO3 nanoparticles.


Biodegradable Materials and Green Processing for Green Electronics

In the article at Advanced Materials (DOI:10.1002/adma.202001591), recent research progress in biodegradable materials and green processing for green electronics is comprehensively. The biodegradable materials used for different functional layers and green/nontoxic processing for solar cells, organic field‐effect transistors, light‐emitting devices, and other devices are discussed in detail. Future development and a perspective of green electronics are also proposed and presented.

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Fully Inorganic CsSnI3‑Based Solar Cells with >6% Efficiency

In the article at ACS Applied Materials & Interfaces (DOI:10.1021/acsami.0c16634), a mixed electron transport layer (ETL) composed of ZnO nanoparticles and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) is incorporated into inorganic black orthorhombic (B-γ) CsSnI3 PSCs. The mixed ETL exhibits merits of both ZnO and PCBM. As a result, the highest PCE of 6.08% was recorded for the PSC with mixed ZnO-PCBM ETL, which is 34.2% higher than that of device with plain PCBM ETL (PCE of 4.53%) and 28.8% higher than that of device with plain ZnO ETL (PCE of 4.72%).

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Hole Transporting Materials by “Flexible Core with Tunable Conformation (FCTC)” strategy for Perovskite Solar Cell

In the article at Solar RRL (DOI:10.1002/solr.202000327), new dopant-free hole transporting materials (HTMs) are designed based on “flexible core with tunable conformation (FCTC)” strategy for perovskite solar cell. With the flexible core, the HTMs can tune their configurations based on the interactions between side arms and perovskite or interactions between side arms themselves, which may lead to a good balance of mobility and charge recombination.

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Water-dispersible Conducting Polyazulene for Thermoelectrics

In the article at ChemComm (DOI:10.1039/d0cc03840g), water-dispersible conducting polymer polyazulene-polystyrenesulfonate (PAZ:PSS) is synthesized using PSS as template. PAZ:PSS can achieve overall conductivity up to 0.1 Scm-1,  and ion Seebeck coefficient as high as 4,500 μVK-1, demonstrating that PAZ:PSS is another promising water-dispersible polymer for thermoelectrics.


High-Performance Inverted Planar Perovskite Solar Cells Enhanced by Thickness Tuning of New Dopant-free Hole Transporting Layer

In the article at Small (DOI:10.1002/smll.201904715), a new hole transporting material (HTM) 4,4',4'',4'''-([9,9'-bifluorenylidene]-2,2',7,7'-tetrayl)tetrakis(N,N-bis(4-methoxyphenyl)aniline) named DMZ is synthesized and employed as a dopant-free HTM in inverted planar perovskite solar cells (PSCs). Systematic studies demonstrate that the thickness of HTL can effectively enhance the morphology and crystallinity of perovskite layer, leading to low series resistance and less defects in the crystal. As a result, the champion power conversion efficiency (PCE) of 18.61% is achieved with a thickness of ~ 13 nm of DMZ (2 mg/mL) under standard AM 1.5G illumination,


Passivation of Perovskite with Organophosphorus Ligands

In the article at Solar Energy Materials and Solar Cells (DOI:10.1016/j.solmat.2020.110527), organophosphorus ligands, trioctylphosphine oxide (TOPO) and triphenylphosphine oxide (TPPO), are used as passivators through antisolvent process for the interfacial modification. The organophosphorus ligands can effectively passivate the defects of perovskite crystals through the formation of Pb-O bond between organophosphorus ligand and undercoordinated Pb2+ ion in perovskite. Moreover, benzene rings with pi-electron in TPPO facilitate the charge transfer between perovskite and hole-transporting layer,  achieving the best power conversion efficiency of 18.29% with negligible hysteresis.


Passivation of Perovskite with Fluorinated Polymer

In this work, we applied dithienobenzodithiophene-based π-conjugated polymer consisting of fluorinated benzotriazole and benzothiadiazole through anti-solvent method to passivate the defects of perovskite crystals. The fluorinated polymer interacts with under coordinated Pb2+ ions in the perovskite crystals to form Pb-F bond which effectively passivates the defects. As a result, a power conversion efficiency (PCE) of 18.03% is achieved in the champion cell. Moreover, the defect passivation blocks the pathway for moisture to diffuse into perovskite film, preventing the decomposition of the perovksite crystal. Therefore, the device retains 90% of the original PCE even after storing in an ambient environment with 60% relative humidity for 1000 h. The related work was published in Solar RRL, DOI: 10.1002/solr.201900029 and highlighted at MaterialsViewsChina (

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Saddle-shaped Small Molecule as Bi-functional Hole Transporting Layer (HTL) 

In the collaboration work with Prof Li Gongqiang from Nanjin Tech University, we design and synthesize a saddle-shaped organic small molecule named α, β-COTh-Ph-OMeTAD. This bi-functional small molecule serves as a dopant-free HTL as well an interfacial layer to passivate the perovskite. With the dopant-free α, β-COTh-Ph-OMeTAD as a HTM and an interfacial layer, the perovskite solar cells (PSCs) exhibits a power conversion efficiency PCE of 17.22%, which is higher than that of device based-on conventional, doped spiro-OMeTAD (16.83%). Our work opens a new avenue for efficient and stable PSCs by exploring new dopant-free materials as alternatives to spiro-OMeTAD. The related work was published in Solar RRL, DOI:10.1002/solr.201900011


E-skin Project by Undergraduate Students

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Kyaw Research Group
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