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1. New Chalcogenide-Based Hole Transport Materials for Colloidal Quantum Dot Photovoltaics

   Rong, Eric; Bambini, Christianna; Lin, Yida; Lu, Chengchangfeng; Thon, Susanna M. (January 2021, Conference record of the IEEE Photovoltaic Specialists Conference)

   null (Ed.)

   Colloidal Quantum Dot (CQD) thin films are ad- vantageous for solar energy generation because of their low- cost and size-tunable, solution-processable nature. However, their efficiency in solar cells is limited in part by the performance of the hole transport layer (HTL). Through Solar Cell Capacitance Simulations and Transfer Matrix Method calculations, we show that significant photogeneration occurs in the standard HTL of ethanedithiol-passivated lead sulfide CQDs which is a problem due to the sub-optimal carrier mobility in this material. We report new HTLs composed of chalcogenide-based materials to address these issues, and demonstrate an absolute power conversion efficiency improvement of 1.35% in the best device. 

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2. 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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3. 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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4. Improving the Performance and Yield of Colloidal Quantum Dot Solar Cells Through Electron Transport Layer Optimization

   https://doi.org/10.1109/PVSC48320.2023.10359662  

   Kachman, Dana; Chiu, Arlene; Gudi, Dhanvini; Lu, Chengchangfeng; Rong, Eric; Chintapalli, Sreyas; Lin, Yida; Khurgin, Daniel; Thon, Susanna M (June 2023, IEEE)

   Colloidal quantum dots (CQDs) are promising materials for photovoltaic applications due to their solution processibility and size-dependent band gap tunability. The electron transport layer (ETL) is an important component of PbS CQD solar cells, and the quality of the zinc oxide nanoparticle (ZnO NP) ETL film significantly impacts both the power conversion efficiency (PCE) and fabrication yield of CQD solar cells. We report on multiple methods to improve the quality of ZnO NP ETL films and demonstrate increased PCE and device yield in standard CQD solar cells employing optimized ZnO NP films. We also discuss the application of these methods in an inverted CQD solar cell architecture. 

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5. Spectrally-selective Photovoltaics via Photonic Band Engineering in Absorbing Media

   https://doi.org/10.1109/PVSC40753.2019.8980467  

   Chiu, Arlene; Qiu, Botong; Lin, Yida; Arinze, Ebuka S.; Li, Lulin; Thon, Susanna M. (June 2019, Spectrally-selective Photovoltaics via Photonic Band Engineering in Absorbing Media)

   Spectral selectivity is of interest for many photovoltaic applications, such as in multijunction and transparent solar cells, where wavelength-selectivity of the photoactive material is necessary. We investigate using artificial photonic band engineering as a method for achieving spectral selectivity in an absorbing material such as PbS CQD thin films. Using FDTD simulations, we find that a CQD-based photonic crystal (CQD-PC) is able to maintain its photonic band structure, including the existence of a reduced photonic density of states, in the presence of weak material absorption. This shows that CQD-PCs are a promising material for photovoltaic applications that require spectral selectivity. 

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