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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. Robust Molecular Dipole‐Enabled Defect Passivation and Control of Energy‐Level Alignment for High‐Efficiency Perovskite Solar Cells

   https://doi.org/10.1002/anie.202105512  

   Wang, Bing; Li, Hong; Dai, Qingqing; Zhang, Meng; Zou, Zhigang; Brédas, Jean‐Luc; Lin, Zhiqun (June 2021, Angewandte Chemie International Edition)

   Abstract The ability to passivate defects and modulate the interface energy‐level alignment (IEA) is key to boost the performance of perovskite solar cells (PSCs). Herein, we report a robust route that simultaneously allows defect passivation and reduced energy difference between perovskite and hole transport layer (HTL) via the judicious placement of polar chlorine‐terminated silane molecules at the interface. Density functional theory (DFT) points to effective passivation of the halide vacancies on perovskite surface by the silane chlorine atoms. An integrated experimental and DFT study demonstrates that the dipole layer formed by the silane molecules decreases the perovskite work function, imparting an Ohmic character to the perovskite/HTL contact. The corresponding PSCs manifest a nearly 20 % increase in power conversion efficiency over pristine devices and a markedly enhanced device stability. As such, the use of polar molecules to passivate defects and tailor the IEA in PSCs presents a promising platform to advance the performance of PSCs. 

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5. High‐Performance Tandem Organic Solar Cells Using HSolar as the Interconnecting Layer

   https://doi.org/10.1002/aenm.202000823  

   Ho, Carr Hoi Yi; Kim, Taesoo; Xiong, Yuan; Firdaus, Yuliar; Yi, Xueping; Dong, Qi; Rech, Jeromy J.; Gadisa, Abay; Booth, Ronald; O'Connor, Brendan T.; et al (May 2020, Advanced Energy Materials)

   Abstract Tandem structure provides a practical way to realize high efficiency organic photovoltaic cells, it can be used to extend the wavelength coverage for light harvesting. The interconnecting layer (ICL) between subcells plays a critical role in the reproducibility and performance of tandem solar cells, yet the processability of the ICL has been a challenge. In this work the fabrication of highly reproducible and efficient tandem solar cells by employing a commercially available material, PEDOT:PSS HTL Solar (HSolar), as the hole transporting material used for the ICL is reported. Comparing with the conventional PEDOT:PSS Al 4083 (c‐PEDOT), HSolar offers a better wettability on the underlying nonfullerene photoactive layers, resulting in better charge extraction properties of the ICL. When FTAZ:IT‐M and PTB7‐Th:IEICO‐4F are used as the subcells, a power conversion efficiency (PCE) of 14.7% is achieved in the tandem solar cell. To validate the processability of these tandem solar cells, three other research groups have successfully fabricated tandem devices using the same recipe and the highest PCE obtained is 16.1%. With further development of donor polymers and device optimization, the device simulation results show that a PCE > 22% can be realized in tandem cells in the near future. 

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