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1. Improving PbS Colloidal Quantum Dot Solar Cell Performance via Solution-Phase Engineering

   https://doi.org/10.1109/PVSC48320.2023.10359532  

   Gudi, Dhanvini; Chiu, Arlene; Kachman, Dana; Rong, Eric; Kamal, Serene; Lan, Yucheng; Thon, Susanna M (June 2023, IEEE)

   Lead Sulfide (PbS) colloidal quantum dots (CQDs) are promising materials for flexible and wearable photovoltaic devices and technologies due to their low cost, solution processibility and bandgap tunability with quantum dot size. However, PbS CQD solar cells have limitations on performance efficiency due to charge transport losses in the CQD layers and hole transport layer (HTL). This study pursues two promising techniques in parallel to address these challenges. Solution-phase annealing of the absorbing PbS-PbX2 (X = Br, I) layer can reduce charge transport losses by removing oleic acid and parasitic hydroxyl ligands. Additionally, optoelectronic simulations are used to show that HTL performance can be improved by the addition of a 2D transition metal dichalcogenide (TMD) layer to the PbS CQD-based HTL. We use solution-phase exfoliation to produce and incorporate 2D WSe2 nanoflakes into the HTL. We report a power conversion efficiency (PCE) increase of up to 3.4% for the solution-phase-annealed devices and up to 1% for the 2D WSe2 HTL augmented devices. A combination of these two techniques should result in high-performing PbS CQD solar cells, paving the way for further advancements in flexible photovoltaics. 

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2. Solution-processed vanadium oxides as a hole-transport layer for Sb2Se3 thin-film solar cells

   https://doi.org/https://doi.org/10.1016/j.solener.2021.11.009  

   AlAmina, LipingGuoa (January 2022, Solar energy)

   Antimony selenide (Sb2Se3) is a promising light absorber material for solar cells because of its superior photovoltaic properties. However, the current performance of the Sb2Se3 solar cell is much lower than its theoretical value (∼32%) due to its low open-circuit voltage (VOC). In this paper, we have demonstrated inorganic vanadium oxides (VOx) as a hole transport layer (HTL) for Sb2Se3 solar cells to enhance efficiency through the VOC improvement. Here, a solution-processed VOx through the decomposition of the triisopropoxyvanadium (V) oxide is deposited on the Sb2Se3 absorber layer prepared by close-spaced sublimation (CSS). With VOx HTL, the built-in voltage (Vbi) is significantly increased, leading to improved VOC for the Sb2Se3 solar cell devices. As a result, the efficiency of the device increases from an average efficiency of 5.5% to 6.3% with the VOx. 

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3. New Hole Transport Materials via Stoichiometry-Tuning for Colloidal Quantum Dot Photovoltaics

   https://doi.org/10.1109/PVSC45281.2020.9300891  

   Chiu, Arlene; Bambini, Christianna; Rong, Eric; Lin, Yida; Thon, Susanna M. (June 2020, 2020 IEEE 47th Photovoltaic Specialists Conference (PVSC))

   Colloidal quantum dots (CQDs) are of interest for photovoltaic applications such as flexible and multijunction solar cells, where solution processability and infrared absorption are crucial; however, current CQD solar cell performance is limited by the hole transport layers (HTLs) used in the cells. We report on a method to develop new HTLs for the highest-performing PbS CQD solar cell architecture by tuning the stoichiometry via sulfur infiltration of the p-type CQD HTL to increase its doping density and carrier mobility. Using SCAPS simulations, we predict that increased doping density and mobility should improve the performance of the solar cells. We show that sulfur doping of the current HTL is a facile and effective method to boost the performance of CQD photovoltaics. 

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4. Machine learning enhanced characterization and optimization of photonic cured MAPbI ₃ for efficient perovskite solar cells

   https://doi.org/10.20517/jmi.2024.72  

   Allen, Cody R; Bhandari, Bishal; Xu, Weijie; Lee, Mark; Hsu, Julia_W P (December 2024, Journal of Materials Informatics)

   Photonic curing (PC) can facilitate high-speed perovskite solar cell (PSC) manufacturing because it uses high-intensity light pulses to crystallize perovskite films in milliseconds. However, optimizing PC conditions is challenging due to its many variables, and using power conversion efficiency (PCE) as the optimization metric is both time-consuming and labor-intensive. This work presents a machine learning (ML) approach to optimize PC conditions for fabricating methylammonium lead iodide (MAPbI3) films by quantitatively comparing their ultraviolet-visible (UV-vis) absorbance spectra to thermal annealed (TA) films using four similarity metrics. We perform Bayesian optimization coupled with Gaussian process regression (BO-GP) to minimize the similarity metrics. Refining PC conditions using active learning based on BO-GP models, we achieve a PC MAPbI3 film with an absorbance spectrum closely matching a TA reference film, which is further verified by its crystalline and morphological properties. Thus, we demonstrate that the UV-vis absorption spectrum can accurately proxy film quality. Additionally, we use an AI-based segmentation model for a more efficient grain size analysis. However, when we use the optimized PC condition to fabricate PSCs, we find that interaction between MAPbI3 and the hole transport layer (HTL) during PC critically degrades the PSC performance. By adding a buffer layer between the HTL and MAPbI3, the optimized PC PSCs produce a champion PCE of 11.8%, comparable to the TA reference of 11.7%. Using UV-vis similarity metrics instead of device PCE as the objective in our BO-GP method accelerates the optimization of PC processing conditions for MAPbI3 films. 

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5. Chemical and Biological Solutions to the Thermodynamic Challenges Posed by Hydrothermal Liquefaction Process Water

   https://doi.org/10.1088/2516-1083/addc31  

   Lin_Htun, San; Adair, James; Goldfarb, Jillian L (May 2025, Progress in Energy)

   Its ability to upconvert myriad wet carbonaceous wastes into biofuels and platform chemicals makes Hydrothermal Liquefaction (HTL) an attractive process to incorporate into a future bioeconomy. However, while HTL is well suited to process feedstocks with high moisture content, it generates a carbon-laden process water (PW). There is considerable research on the state-of-the-field of HTL; the impact of feedstocks and process conditions on products is well established, as are methods to upgrade recovered biocrudes. However, methods to efficiently separate, recover, and utilize the fugitive carbon in PW are less well understood. We believe this is because of the intrinsic thermodynamic limitations imposed by the PW; PW is a solutropic solution for which liquid-liquid extraction is, depending on the solvent, of minimal utility. Aqueous phase processing and electrocatalytic oxidation could produce high-value products like H2 for biocrude upgrading, though issues of catalyst stability and electrode fouling, along with selectivity and efficiency, plague these nascent technologies. The literature is replete with conflicting opinions on the potential to recycle PW in the reactor (some authors find enhancement of hydrochar or biocrude yield, others no change or a negative impact). The current Edisonian approach to biological treatment (e.g. grow one bacteria on one PW) leaves the field without a clear understanding of the HTL PW compounds that inhibit or promote growth beyond broad classifications. Through this review, we hope to encourage the HTL field to move beyond the current norm of processing singular feedstocks to assess the biocrude produced and consider the carbon balance of the entire system to develop recovery and valorization pathways for the carbon present in HTL PW. 

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