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1. Solution-processed broadband photodetectors without transparent conductive oxide electrodes

   https://doi.org/10.1039/D1TC04278E  

   Sheng, Lening; Yi, Chao; Zheng, Luyao; Liu, Yanghe; Zheng, Jie; Gong, Xiong (February 2022, Journal of Materials Chemistry C)

   Broadband photodetectors (PDs) have great applications in both industrial and scientific sectors. In this study, solution-processed broadband PDs with an “inverted” vertical photodiode device structure without incorporating transparent conductive oxides electrodes, fabricated by bulk heterojunction (BHJ) composites composed of a low optical gap conjugated polymer blended with highly electrically conductive PbS quantum dots (QDs), operated at room temperature, are reported. The low optical gap conjugated polymer incorporated with PbS QDs contributes to the spectral response from the ultraviolet (UV)-visible to the infrared (IR) range. To realize the IR spectral response and to circumvent the weak IR transparency of the transparent oxide electrodes, the implementation of a photodiode with an “inverted” vertical device structure with the Au anode and the Ba/Al bilayer semitransparent cathode passivated with the MgF 2 layer is demonstrated. Photoinduced charge carrier transfer occurring within the BHJ composite gave rise to decent photocurrent, resulting in detectivities greater than 10 12 Jones (cm Hz 1/2 /W) over the wavelength from the UV-visible to the IR range under low applied bias. Thus, our findings of the utilization of the BHJ composites and an “inverted” vertical photodiode without the incorporation of the transparent conductive oxide electrodes provide a facile way to realize broadband PDs. 

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2. Perspective on integrated photonic devices using transparent conductive oxides: Challenges and opportunities

   https://doi.org/10.1063/5.0179441  

   Wang, Alan X; Hsu, Wei-Che (February 2024, Applied Physics Letters)

   Transparent conductive oxides (TCOs) are gaining increasingly high research interest for integrated photonic devices due to the strong plasma dispersion effect and process compatibility with versatile optoelectronic platforms. In this perspective article, the authors gave a brief review of research efforts both on theoretical modeling and experimental demonstration of integrated photonic devices, especially on high-efficiency electro-optic modulators through the integration with plasmonics and silicon photonics. In addition, the authors discussed the challenge and opportunity associated with TCO photonic devices and the application in photonic integrated circuits (PICs) with emphasis on high mobility materials, high-speed E-O modulators, and large-scale integration. Finally, we conclude that collaboration with existing silicon photonics foundry is a necessary route to incorporate TCOs into existing PIC ecosystems. 

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3. High-Pressure Polymorphism in Silver Ferrite Delafossite, AgFeO ₂

   https://doi.org/10.1021/acs.inorgchem.3c04631  

   Manganaro, Nicholas S; Ambos, Scott D; DeCapua, Matthew; Thiel, Scott D; Mitchell, Wyatt E; Liu, Zhenxian; Zhang, Dongzhou; Nguyen, Phuong_Q H; Lavina, Barbara; Alp, Esen Ercan; et al (May 2024, Inorganic Chemistry)

   The delafossites are a class of layered metal oxides that are notable for being able to exhibit optical transparency alongside an in-plane electrical conductivity, making them promising platforms for the development of transparent conductive oxides. Pressure-induced polymorphism offers a direct method for altering the electrical and optical properties in this class, and although the copper delafossites have been studied extensively under pressure, the silver delafossites remain only partially studied. We report two new high-pressure polymorphs of silver ferrite delafossite, AgFeO2, that are stabilized above ∼6 and ∼14 GPa. In situ X-ray diffraction and vibrational spectroscopy measurements are used to examine the structural changes across the two phase transitions. The high-pressure structure between 6 and 14 GPa is assigned as a monoclinic C2/c structure that is analogous to the high-pressure phase reported for AgGaO2. Nuclear resonant forward scattering reveals no change in the spin state or valence state at the Fe3+ site up to 15.3(5) GPa. 

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4. Printing flexible two-dimensional indium tin oxide for multifunctional transparent bioelectrodes

   https://doi.org/10.1557/s43580-025-01320-w  

   Rahman, Md Saifur; Ong, Samuel A; Tiwari, Anand P; Scheideler, William J (June 2025, MRS Advances)

   Transparent conductive oxides (TCOs) are a high-performance material system that could enable new wearable sensors and electronics, but traditional fabrication methods face scalability and performance challenges. In this work, we utilize liquid metal printing to produce ultrathin two-dimensional (2D) indium tin oxide (ITO) films with superior microstructural, optical, and electrical properties compared to conventional techniques. We investigate the dynamics of grain growth and its influence on conductivity and the optical properties of 2D ITO, demonstrating the tunability through annealing and multilayer deposition. Additionally, we develop Au-decorated transparent electrodes, showcasing their adhesion and flexibility, low contact impedance, and biocompatibility. Leveraging the transparency of these electrodes, we enable enhanced simultaneous multimodal biosignal acquisition by integrating biopotential-based methods, such as electrocardiogram (ECG) or bioimpedance sensing (e.g., impedance plethysmography, IPG), with optical modalities like photoplethysmography (PPG). This study establishes CLMP-fabricated flexible 2D TCOs as a versatile platform for advanced bioelectronic systems and multimodal diagnostics. 

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5. Band Gap Tuning of Films of Undoped ZnO Nanocrystals by Removal of Surface Groups

   https://doi.org/10.3390/nano12030565  

   Zhang, Chengjian; Tu, Qiaomiao; Francis, Lorraine F.; Kortshagen, Uwe R. (February 2022, Nanomaterials)

   Transparent conductive oxides (TCOs) are widely used in optoelectronic devices such as flat-panel displays and solar cells. A significant optical property of TCOs is their band gap, which determines the spectral range of the transparency of the material. In this study, a tunable band gap range from 3.35 eV to 3.53 eV is achieved for zinc oxide (ZnO) nanocrystals (NCs) films synthesized by nonthermal plasmas through the removal of surface groups using atomic layer deposition (ALD) coating of Al2O3 and intense pulsed light (IPL) photo-doping. The Al2O3 coating is found to be necessary for band gap tuning, as it protects ZnO NCs from interactions with the ambient and prevents the formation of electron traps. With respect to the solar spectrum, the 0.18 eV band gap shift would allow ~4.1% more photons to pass through the transparent layer, for instance, into a CH3NH3PbX3 solar cell beneath. The mechanism of band gap tuning via photo-doping appears to be related to a combination of the Burstein–Moss (BM) and band gap renormalization (BGN) effects due to the significant number of electrons released from trap states after the removal of hydroxyl groups. The BM effect shifts the conduction band edge and enlarges the band gap, while the BGN effect narrows the band gap. 

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