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Öğe Applications of carbon-based materials for ımproving the performance and stability of perovskite solar cells(John Wiley and Sons Inc., 2023) Patel, Krina; Prochowicz, Daniel; Akın, Seçkin; Kalam, Abul; Tavakoli, Mohammad Mahdi; Yadav, PankajOrganic–inorganic hybrid perovskite solar cells (PSCs) attract many researchers in the field of photovoltaic because of their high-power conversion efficiency and low-cost manufacturing. However, improper interfacial charge transfer, perovskite degradation, and poor stability are major concerns for their commercialization and scale-up. Significant efforts have been made in recent years mainly by employing different strategies such as optimizing fabrication, developing novel materials, use of additives, and an interfacial layer in PSCs. Nowadays, carbon materials are widely recognized as promising candidates for alternative usage in PSCs because of their cost effectiveness, high conductivity, appropriate work function (5.0 eV), and low-temperature sintering process. In addition, the highly hydrophobic nature of the carbon-based materials prevents moisture penetration into the perovskite layer, resulting in enhanced stability. This review shows how effectively carbon-based materials can improve the performance of PSCs. First, the different carbon materials such as graphene and its derivatives, fullerenes and its derivatives, carbon quantum dots, and carbon nanotubes are described. Subsequently, the role of these carbon-based materials employed in electron-transport layers, hole-transport layers, and perovskite layers in PSCs is discussed. Thus, this review highlights the recent advancements made in carbon-based PSCs and their role in improving the performance of PSCs.Öğe Investigation on the facet-dependent anisotropy in halide perovskite single crystals(American Chemical Society, 2022) Parikh, Nishi; Pandey, Manoj; Prochowicz, Daniel; Kalam, Abul; Tavakoli, Mohammad Mahdi; Satapathi, Soumitra; Akın, Seçkin; Yadav, PankajMetal halide perovskite (MHP) single crystals (SCs) are proven to possess superior optoelectronic properties compared to those of their polycrystalline thin film analogues. With the advancement and progress in the study of MHP SCs, it is found that the properties at the surface and bulk of SCs are significantly different. However, there are only a few studies present for the facet-dependent performance of MHP SCs. In this work, we have systematically investigated the anisotropic properties of naturally exposed facets ((100) and (112)) in MAPbI3 SCs. We studied the influence of temperature and illumination on the properties of these facets. It was found that hysteresis at the (112) facet is higher than that at the (100) facet because of the higher trap density of 1.17 × 1013 cm-3 at this facet as compared to the trap density of 2.11 × 1012 cm-3 for the (100) facet. Although there exist different kinds of defects at both the facets, the ion migration mechanism remains the same at both facets, which is confirmed by the obtained almost same activation energy of 0.378 and 0.308 eV for (100) and (112) facets, respectively, for ion migration. The photocurrent, responsivity, and EQE values further confirm anisotropic properties of both the facets in MAPbI3 SCs although they are the same from the crystallography point of view. Thus, this study provides a detailed and systematic investigation of the facet-dependent properties in MHP SCs.Öğe Probing the low-frequency response of ımpedance spectroscopy of halide perovskite single crystals using machine learning(American Chemical Society, 2023) Parikh, Nishi; Akın, Seçkin; Kalam, Abul; Prochowicz, Daniel; Yadav, PankajElectrochemical impedance spectroscopy (EIS) has emerged as a versatile technique for characterization and analysis of metal halide perovskite solar cells (PSCs). The crucial information about ion migration and carrier accumulation in PSCs can be extracted from the low-frequency regime of the EIS spectrum. However, lengthy measurement time at low frequencies along with material degradation due to prolonged exposure to light and bias motivates the use of machine learning (ML) in predicting the low-frequency response. Here, we have developed an ML model to predict the low-frequency response of the halide perovskite single crystals. We first synthesized high-quality MAPbBr3 single crystals and subsequently recorded the EIS spectra at different applied bias and illumination intensities to prepare the dataset comprising 8741 datapoints. The developed supervised ML model can predict the real and imaginary parts of the low-frequency EIS response with an R2 score of 0.981 and a root mean squared error (RMSE) of 0.0196 for the testing set. From the ground truth experimental data, it can be observed that negative capacitance prevails at a higher applied bias. Our developed model can closely predict the real and imaginary parts at a low frequency (50 Hz-300 mHz). Thus, our method makes recording of EIS more accessible and opens a new way in using the ML techniques for EIS.Öğe Probing the surface and bulk electrical response of MAPbBr3Single crystals(American Chemical Society, 2022) Yadav, Pankaj; Parikh, Nishi; Prochowicz, Daniel; Kalam, Abul; Tavakoli, Mohammad Mahdi; Akın, SeçkinSingle crystals (SCs) of halide perovskites are rapidly gaining attention over their polycrystalline thin-film counterparts due to their superior optoelectronic properties. One of the various reasons for their improved properties is the reduced defect concentration as compared with thin films. Since their discovery, many efforts have been devoted to discerning the surface and bulk properties of SCs. However, it is difficult to probe the surface and bulk responses of SCs, and only a few reports distinguishing between these properties have been presented. In this study, we distinguished between the surface and bulk electrical responses of methylammonium lead tribromide (MAPbBr3) SCs using impedance spectroscopy (IS). The electrical response of the MAPbBr3SC was recorded using different optical excitations for the generation of carriers. The Nyquist plots and capacitance-frequency responses observed under blue and red wavelengths differ significantly from each other and were studied systematically. The results obtained suggest that the photocurrent and capacitive response under blue light are higher than those under red light. Moreover, the change in the low-frequency capacitance is lower in the case of blue light. This is because of the polarization of the interface of metal contacts and the surface of SCs or due to defect-mediated conductivity. As the carriers are collected efficiently from the surface following a rapid process, they do not contribute to the capacitance build-up with temperature. To the best of our knowledge, electrical responses such as the impedance and the capacitive response of SCs using different illumination wavelengths and temperatures have been rarely discussed in the literature. © 2022 American Chemical Society. All rights reserved.Öğe Recent progress of light intensity-modulated small perturbation techniques in perovskite solar cells(John Wiley and Sons Inc, 2021) Parikh, Nishi; Narayanan, Saranya; Kumari, Hemant; Prochowicz, Daniel; Kalam, Abul; Satapathi, Soumitra; Akın, SeçkinThe small perturbation frequency-resolved techniques have been powerful tools in unraveling the kinetic processes governing the operation of perovskite solar cells (PSCs). One such technique is electrochemical impedance spectroscopy (EIS). However, a thorough interpretation of the EIS response of PSCs is still lacking owing to the absence of a uniform electrical equivalent circuit. In this context, intensity-modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS) can be the link between the optical and electrical responses of PSCs and complement the IS technique. In this review, the progress made in interpreting the IMPS/IMVS response of various types of PSCs is summarized and diverse prospects are discussed. First, the basic theory and models present in the literature are discussed. Next, the IMPS/IMVS response of mesoporous and planar PSCs based on various physical parameters is discussed. At last, proposed future prospects for the development of this field are discussed.
