記住我
Aloke Verma1*
, Shilpi Shrivastava2, Anushree Saha2 and Swapnil Jain 3
1Department of Physics, Kalinga University, Naya Raipur (CG) India.
2Department of Chemistry, Kalinga University, Naya Raipur (CG) India.
3Department of Mechanical Engineering, Kalinga University, Naya Raipur (CG) India.
Corresponding Author E-mail: alokeverma1785@gmail.com
Article Publishing History
Article Received on : 26 Oct 2023
Article Accepted on :
Article Published : 09 Jan 2024
In recent studies, researchers have explored the use of carbazole-based self-assembled monolayers (SAM) as hole transport layer (HTL) in perovskite solar cell (PSC). Still, their application in Sn or mixed Sn/Pb PSCs has faced challenges due to the underprivileged perovskite solderability indicant solution on the surface of carbazole. In response to this study introduces a novel approach using a self-assembled bilayer (SAB) composed of a covalent monolayer (Br-2PACz) and a noncovalent solderability layer (4CzNH3I) as the HTL in Cs1/4FA3/4Sn1/2Pb1/2I3 PSCs. Additionally, the ammonium groups in the solderability layer contribute to the deactivation of state of trap at the camouflaged SAB/ABO3 interface. The incorporation of SAB significantly improves accuracy of perovskite solar devices, resulting in moderate efficiency of 18.98 ± 0.28%. SAM-only devices exhibit lower efficiency, with moderate value of 11.54 ± 9.36%. Furthermore, the enhanced processability of the perovskite on the SAB leads to improved reproducibility for larger-sized devices. Improved perovskite processability on SAB results in improved reproducibility of larger devices, yielding a 12.5% efficiency for a 0.8 cm2 active area device. Lastly, the operational stability of the devices is extended, with the SAB-based SCs demonstrating a T80% operational stability of 358 hours, compared to 220 hours for the SAM-based counterparts.
KEYWORDS:Carbazole-based SAM; Device reproducibility; Operational stability; PSCs; Surface energy tuning; Sn/Pb mixed perovskite; Wetting layer
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Copy the following to cite this article:Verma A, Shrivastava S, Saha A, Jain S. The Efficiency Enhancement of Perovskite Solar Cells with Carbazole Self-Assembled Monolayers in Hole Transport Layers. Orient J Chem 2024;40(1).
Verma A, Shrivastava S, Saha A, Jain S. The Efficiency Enhancement of Perovskite Solar Cells with Carbazole Self-Assembled Monolayers in Hole Transport Layers. Orient J Chem 2024;40(1). Available from: https://bit.ly/41OTvEQ
Introduction
Organic-inorganic metal halide PSC have shown significant advancements in device efficiency, reaching a record-high efficiency of 26.08%. However, these devices face challenges in long-term stability and large-area devices with comparable efficiency levels. Excellent mixed Sn/Pb PSCs efficiency of 23.7% use p-i-n assembly with poly[3,4-ethylenedioxythiophene] (PEDOT) and polystyrene sulfonate (PSS) as HTL. Concerns exist regarding the use of PEDOT:PSS right to its absorbent and corrosive manner, potentially impacting long-term device stability [1]. Alternative materials like PTAA and NiOx have been explored as HTLs in mixed Sn/Pb PSCs, but have exhibited poor device replication. Carbazole-based Self-Assembled Monolayers (SAMs) are utilized as hole transport layers in organic electronic devices due to their electron-donating properties, stability, and durability. Therefore, a potential solution for safer, more efficient and financially scalable HTL is the use of carbazole-based SAM [2]. Carbazole-based monolayers have proven successful in Pb-based PSCs and Si-perovskite tandem devices. Nevertheless, limited research has focused on employing SAMs like exacting contacts in Sn/Pb perovskite devices mixed. To address this challenge, a Br-2PACz SAM is introduced as an HTL in Cs1/4FA3/4Sn1/2Pb1/2I3 PSCs. This approach improves scalability of devices, enabling full active area coverage, leading to devices with efficiencies of 12.5% [3].
Experimental Method:
In this research, all the chemicals used are AR-grade and 99.99% pure. The study used hole transport layer (HTL) Br-2PACz molecules on an ITO substrate. Using the liquid phase deposition method to create a uniform monolayer result in a densely packed and well-ordered monolayer. A washing step was conducted to eliminate non-covalently attached molecules, yielding a homogeneous monolayer. The ultimate thickness of Br-2PACz atomic plane was approximately 1 nm [4]. To enhance the surface polarity of the HTL and facilitate the formation of a uniform polycrystalline perovskite layer, a solderability layer composed of 4NH3CzI molecules was introduced onto the Br-2PACz layer [5]. The surface energy of the HTL can be altered by these organic cations, which consist of a four-unit methylene chain with NH4+ group the alkyl spacer is appended at the terminus. This modification does not negatively impact the advantageous transport properties of the Br-2PACz SAM. We added a layer that could be soldered by spin coating a 1 mg/ml solution of ethanol of 4CzNH3I on top (see Figure 1b). The idea behind our study was that the two carbazole structures found in Br-2PACz and 4CzNH3I would interact with each other and form a sandwich-like structure [6]. This arrangement exposes ammonium groups on the surface, significantly improving the ability of the Cs1/4FA3/4Sn1/2Pb1/2I3 solution of precursor in DMF and DMSO to spread and adhere [7].
Figure 1: a) A schematic illustration of the liquid-phase and b) spin coating techniques
utilized in the 4CzNH3I deposition process.
Figure 2A: (a, b). Contact angle of Cs1/4FA3/4Sn1/2Pb1/2I3 perovskite solution droplets on ITO/Br-2PACz and ITO/Br-2PACz/4CzNH3I surfaces with photographs of spin-coated thin films.
Results and Discussion
The study investigates the wetting behavior of perovskite precursors on Br-2PACz SAM and SAB. Figure 2 (a, b) shows the contact angle measurement and schematics of perovskite solution of Cs1/4FA3/4Sn1/2Pb1/2I3 [8 – 10]. The results showed a contact angle of 18° for a droplet of perovskite solution on the Br-2PACz monolayer, while it decreased to 3.3° on uppermost of SAB, indicating a transition to a more polar surface. This explains the continuous perovskite film on SAB surface, while the perovskite coverage remains discontinuous on the Br-2PACz monolayer [11–13]. The study also conducted XPS analysis on three samples to confirm the presence of an ammonium-rich surface.
Figure 2B: (c, d, e) The data includes XPS spectra for ITO/Br-2PACz and ITO/Br-2PACz/4CzNH3I trials, with fitting results for C–N═C and C-NH3 peaks.
The study focuses on the identification of ammonium groups in self-assembled monolayer (SAM) and sandwich-assembled bilayer (SAB) samples. The N1s core level spectra from ITO/Br-2PACz and SAB samples show a single peak at 399.1 eV, confirming the occurrence of Br-2PACz surface-bound molecules in ITO [14]. SAB trials also display the identical peak at 399.1 eV and an additional peak at 400.8 eV, indicating a bilayer surface containing ammonium groups. Because the carbon atoms in 4CzNH3I molecules have slightly different chemical properties from those in SAM, they contribute something new to the C1s spectra. When the SAB is formed, a uniform 4CzNH3I layer can be seen in the Br3d core spectra of both the ITO/Br-2PACz and ITO/Br-2PACz/4CzNH3I experiments. In this study, the XPS and contact angle of ITO coated with a 2PACz monolayer and the proposed wetting layer were measured. This demonstrated that this method is applicable to carbazole-based monolayers in general. Br-2PACz and 4CzNH3I interact with one another using AMS-ADF density functional theory calculations at the B3LYP/TZP level. The optical thickness of HTL was estimated using variable-angle spectroscopic ellipsometry (SE); the minimum MSE values imply an optical thickness of 3 nm and a refractive index of 1.73.
The layer produced by spin coating 4CzNH3I molecules has a global thickness of 3 nm and a refractive index in line with previous findings.
Figure 3: (a-d) PL measurements were conducted on ABO3 on Br-2PACz SAM and Br-2PACz/4CzNH3I SAB using two probing approaches: from the perovskite surface crosswise and from the glass crosswise.
The study analyzed the optical and electrical properties of the sandwich-assembled bilayer (SAB) for use in solar cells. Intensity measurements of UV-vis absorption showed an increase between 330 and 435 nm, but ITO’s optical bandgap was unaffected. Kelvin-probe force microscopy was used to analyze the material’s electrical conductivity and work function. Perovskite films made of Cs1/4FA3/4Sn1/2Pb1/2I3 deposited on either SAM or SAB showed identical optical and morphological properties. The active layer quality and interaction with the new HTL were assessed through equilibration and sequential PL spectroscopy [15]. The SAB-based film showed longer charge carrier lifetimes (76.4 ns) compared to the SAM-based film (70.1 ns), attributed to a longer initial decay.
Figure 4A: The device configuration, consisting of ITO/Br2PACz/4CzNH3I/perovskite/C60 /BCP/ITO, is depicted in a schematic and cross-sectional scanning electron microscope image on the right side.
Figure 4B: A devices made with Br-2PACz and Br-2PACz/ 4CzNH3I were analyzed, with special attention paid to their J-V characteristics and PCEs values.
The study fabricated solar cells using two different HTLs, with the Br-2PACz monolayer showing a high short-circuit current VOC, fill factor, and power conversion efficiency [16]. The SAB-based device showed a higher ISC, VOC; fill factor, and power conversion efficiency. The study found that using the SAB as a High-Performance Transistor significantly improved the performance of solar cells. A possible explanation for the passivation of the buried interface and the improved VOC is the decreased number of traps at the SAB/perovskite interlayer. The SAB-based devices also showed lower leakage current (ILL), possibly due to less p-doping of the Pb/Sn system. The most significant improvement was the improved device statistics, with SAB-based SCs exhibiting an average PCE of 18.99 ± 0.29%. The SAB-based SCs also showed improved stability and scalability, with the champion SAB-based SCs retaining 80% of its initial efficiency after 358 hours. Finding a way to improve the wettability of perovskite solutions, according to the study, is essential for increasing the surface area of SAM-based SCs at a large scale [18].
Figure 5: J-V characteristics of Br-2PACz and Br-2PACz/4CzNH3I hole transport layers under AM1.5 G conditions
Conclusion
A method has been developed to improve the deposition of Sn/Pb perovskite active layers on carbazole-based HTLs. This involves applying a layer of 4CzNH3I on a Br-2PACz self-assembled monolayer (SAM), adjusting the surface energy to a more polar state. This results in high-quality Sn/Pb perovskite thin films with excellent reproducibility and reliability. The improved efficiency of SAB-based solar cells is also observed, paving the way for their industrial application.
Acknowledgement
The authors are thanks to Research Lab of Physics and Central Instrumentation Facility (CIF), Kalinga University, Naya Raipur (CG) India for the various characterization.
Conflict of Interest Statement
Aloke Verma, Shilpi Shrivastava, Anushree Saha, and Swapnil Jain conducted ethical and transparent research, demonstrating the importance of ethical practices in scientific research.
References
Pitaro, M., Alonso, J. E. S., Di Mario, L., Romero, D. G., Tran, K., Kardula, J., Zaharia, T., Johansson, M. B., Johansson, E. M. J., Chiechi, R. C., & Loi, M. A. (2023). Tuning the Surface Energy of Hole Transport Layers Based on Carbazole Self‐Assembled Monolayers for Highly Efficient Sn/Pb Perovskite Solar Cells. Advanced Functional Materials, 2306571.
This work is licensed under a Creative Commons Attribution 4.0 International License.
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