Densification and Conductivity of Li-Doped NiO Targets for Hole-Transport Layer of Perovskite Solar Cells

In this review, we will discuss recent progress in metal oxide charge transport layers in perovskite solar cells (PSCs). While a large number of PSCs have at least one metal oxide charge transport layer, here we focus on the progress towards the achievement of high efficiency devices with metal oxide layers prepared under mild deposition conditions, with the ultimate goal being the devices containing metal oxide layer both below and above the perovskite layer to achieve improved stability. Thus, we will provide an overview of recent progress in metal oxides deposited below the perovskite layer (electron transport layers in conventional architecture PSCs, hole transport layers in inverted architecture PSCs), followed by the progress in devices containing both top and bottom metal oxide charge transport layer, and briefly introducing other possible uses of metal oxides in PSCs. For these various applications of metal oxides, we will discuss different approaches (doping, surface treatments, interface modifications) commonly employed to improve device performances, and finally we will provide a brief overview of the characterisation techniques commonly employed to obtain insights into physical mechanisms responsible for the observed device performance. While for several of the experimental techniques extensive reviews exist, this is not the case for all the techniques, and the perovskite literature commonly lacks cautions in interpretation, guidelines on avoiding artefacts, and general overview of what techniques need to be employed for comprehensive device characterisation.

The passivation engineering of the hole transport layer in perovskite solar cells (PSCs) has significantly decreased carrier accumulation and open circuit voltage (Voc) loss, as well as energy band mismatching, thus achieving the goal of high-power conversion efficiency. However, most devices incorporating organic/inorganic buffer layers suffer from poor stability and low efficiency. In this article, we have proposed an inorganic buffer layer of Cu2O, which has achieved high efficiency on lower work function metals and various frequently used hole transport layers (HTLs). Once the Cu2O buffer layer was applied to modify the Cu/PTAA interface, the device exhibited a high Voc of 1.20 V, a high FF of 75.92%, and an enhanced PCE of 22.49% versus a Voc of 1.12 V, FF of 69.16%, and PCE of 18.99% from the (PTAA/Cu) n-i-p structure. Our simulation showed that the application of a Cu2O buffer layer improved the interfacial contact and energy alignment, promoting the carrier transportation and reducing the charge accumulation. Furthermore, we optimized the combinations of the thicknesses of the Cu2O, the absorber layer, and PTAA to obtain the best performance for Cu-based perovskite solar cells. Eventually, we explored the effect of the defect density between the HTL/absorber interface and the absorber/ETL interface on the device and recommended the appropriate reference defect density for experimental research. This work provides guidance for improving the experimental efficiency and reducing the cost of perovskite solar cells.

Characteristics of Mo2C-CNTs hybrid blended hole transport layer in the perovskite solar cells and X-ray detectors

RF sputtered CdS films as independent or buffered electron transport layer for efficient planar perovskite solar cell

In this study, we report the use of ultra-thin VOx film deposited by low temperature (50 °C) atomic layer deposition (ALD) as a hole transport layer (HTL) for perovskite solar cells (PSCs). High efficient PSCs with a power conversion efficiency of 11.53% are achieved with a ∼1 nm VOx layer. It is found that compared to the pristine ALD-VOx films, UV post-treatment significantly enhances the hole transportation ability of the VOx films. To understand the hole transporting mechanism in the VOx films, the ALD-VOx films grown on fluorine-doped tin oxide are investigated by photoelectron spectroscopy. Our investigation confirms that the defect states below the Fermi level of the VOx facilitate hole extractions, and that a greater V5+ oxidation state ratio is found in the UV-treated VOx films. This work shows the potential of using low temperature inorganic VOx films as the HTLs for the application of flexible and large-area PSCs.

An instant p-doping strategy employing 4-tert-butyl-2-chloropyridine and tert-butyl peroxybenzoate for the spiro-OMeTAD hole-transport layer (HTL) in perovskite solar cells (PSCs) is proposed to replace the conventional 4-tert-butylpyridine-doped HTL. The novel doping process eliminates the formation of pores in the HTL. Meanwhile, a 21.4% efficiency is achieved on the corresponding absolute methylammonium-free PSCs with significantly improved thermal and moisture stability.

Organic-inorganic hybrid perovskite photovoltaics are gaining a great attention because of their wide range of applications, while the selection of energy level suitable, high conductivity and commercial hole transport layers is still challenging. Here we familiarize thermally evaporated pristine copper phthalocyanine (CuPc) as hole transport layer in regular perovskite solar cells and validate improved photovoltaic performance, increased stability and uniformity compared to the device without CuPc layer. Here we attempt to develop a scheme for fabricating cost-effective and flexible perovskite solar cells without using a glove box set up.

Nickel oxide (NiO) is used as a hole‐transporting layer (HTL) in perovskite solar cells (PSCs) because of its high optical transmittance, intrinsic p‐type doping, and suitable valence band energy level. However, fabricating high‐quality NiO films typically requires high‐temperature annealing, which limits their applicability for low‐temperature, printable PSCs. Herein, the need for such postprocessing steps is circumvented by coupling 4‐hydroxybenzoic acid (HBA) or trimethyloxonium tetrafluoroborate (Me3OBF4) ligand‐modified NiO nanoparticles (NPs) with a Tesla‐valve microfluidic mixer to deposit high‐quality NiO films at a temperature <150 °C. The NP dispersions and the resulting thin films are thoroughly characterized using a combination of optical, structural, thermal, chemical, and electrical methods. While the optical and structural properties of the ligand‐exchanged NiO NPs remain comparable with those possessing the native long‐chained aliphatic ligands, the ligand‐modified NiO thin films exhibit dramatic reductions in surface energy and an increase in hole mobilities. These are correlated with concomitant and significant enhancements in performance and stability factors of PSCs when the ligand‐modified NiO NPs are used as HTL layers within p−i−n device architectures.

Herein we report a strategy of rapid oxidation of the hole transport layer (HTL) in perovskite solar cells by using oxygen/argon mixture plasma. This strategy offers a promising approach for simple manufacturing, mass production, and industrial applications. Compared to the conventional process of overnight oxidation, only ~10 s of oxygen/argon mixture plasma treatment is enough for the solar cell devices with FTO/ETL/perovskite/HTL/Au structure demonstrating a high power conversion efficiency. It is found that the high concentration of atomic oxygen generated in plasma oxidizing the HTL improves the conductivity and mobility, and therefore the process time is considerably shortened. This novel approach is compatible with continuous mass production, and it is suitable for the fabrication of large-area perovskite solar cells in the future.

In recent years, there has been significant investigation into the high efficiency of perovskite solar cells. These cells have the capacity to attain efficiencies above 14%. As the perovskite materials that include lead pose a substantial environmental risk, components that are free from lead are used during the process of solar cell development. In this work, we use a lead-free double-perovskite material, namely Cs2TiBr6, as the main absorbing layer in perovskite solar cells to enhance power conversion efficiency (PCE). This work is centered on the development of solar cell structures with materials such as an ETL (electron transport layer) and an HTL (hole transport layer) to enhance the PCE. In this theoretical work, we perform simulations and analysis on double-perovskite Cs2TiBr6 to assess its efficacy as an absorber material in various HTLs like Cu2O and CuI, with a fixed ETL of C60 using SCAPS (Solar Cell Capacitance Simulator, SCAPS 3.3.10) Software. This is a one-dimensional solar cell simulation program. In this work, the thickness of the double-perovskite material is also varied between 0.2 and 2.0 µm, and its efficiency is observed. The effect of temperature variation on efficiency in the range of 300 K to 350 K is observed. The effect of defect density on efficiency is also observed in the range of 1 × 1011 to 1 × 1016. In this theoretical work, perovskite solar cells, including their absorbing layer, demonstrate outstanding ETLs and HTLs, respectively. As a result, the cells’ achieved PCE is improved. This work demonstrates the effectiveness of this lead-free double-perovskite structure that absorbs light in perovskite solar cells.

Perovskite solar cells have been researched for high efficiency only in the last few years. These cells could offer an efficiency increase of about 3% to more than 15%. However, lead-based perovskite materials are very harmful to the environment. So, it is imperative to find lead-free materials and use them in designing solar cells. This research investigates the potential for using a lead-free double-perovskite material, La2NiMnO6, as an absorbing layer in perovskite solar cells to enhance power conversion efficiency (PCE). Given the urgent need for environmentally friendly energy sources, the study addresses the problem of developing alternative materials to replace lead-based perovskite materials. Compared to single-perovskite materials, double perovskites offer several advantages, such as improved stability, higher efficiency, and broader absorption spectra. In this research work, we have simulated and analyzed a double-perovskite La2NiMnO6 as an absorbing material in a variety of electron transport layers (ETLs) and hole transport layers (HTLs) to maximize the capacity for high-efficiency power conversion (PCE). It has been observed that for a perovskite solar cells with La2NiMnO6 absorbing layer, C60 and Cu2O provide good ETLs and HTLs, respectively. Therefore, the achieved power conversion efficiency (PCE) is improved. The study demonstrates that La2NiMnO6, as a lead-free double-perovskite material can serve as an effective absorbing layer in perovskite solar cells. The findings of this study contribute to the growing body of research on developing high-efficiency, eco-friendly perovskite solar cell technologies and have important implications for the advancement of renewable energy production.

Perovskite solar cells (PSCs) have demonstrated notable improvements in their power conversion efficiency (PCE), indicating both academic research and commercial application value. The PCE gap is closing when compared to silicon cells sold in stores. Large-scale production, cost, and stability, however, are still far behind. Every functional layer of perovskite solar cells has a range of relevant research for scaling up the preparation of high-efficiency and stable PSCs. The functional layers, such as the electron transport layer, perovskite layer, hole transport layer, and electrode, have been the subject of recent research, which is systematically summarised in this chapter. Significant advancements in device stability and efficiency over the last few decades can be attributed to massive research efforts in compositional, process, and interfacial engineering. We discuss the benefits and drawbacks of PSCs in comparison to the current silicon photovoltaic technology with regard to commercial applications. Moreover, we discuss the structural stability, optical properties, perovskite device structure and operation principle, High efficiency PSCs, Perovskite powder production for diverse application. PSCs provide low manufacturing costs and solution processability, but on the road to commercialization, their poor stability and element toxicity need to be addressed. It is yet unknown how to resolve the costly and unstable issues with electrode materials and Spiro-OMeTAD. There is also discussion of the primary issues and the path for their future growth. In addition, we offer our predictions for PSC commercialization in the solar industry. PSCs are expected to show greater promise in tandem configurations and low-cost modules.

The role of the hole-transport layer (HTL) in CHjNHPbb perovskite solar cells is investigated. It is found that it mainly serves three purposes: First, deposited prior to the gold electrode, it avoids direct contact of the metal electrode with the mesoporous TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> -perovskite layer, and therefore increases the selectivity of the contact. This reduces recombination as evident from an increased open-circuit voltage and a higher luminescence efficiency. Second, the HTL increases the internal quantum efficiency independent of applied voltage and illumination wavelength by reducing (diffusion) losses of charges. Third, due to a smoothing of the TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> -perovskite mesoscopic layer the HTL increases the reflectivity of the gold electrode, allowing for a second path of the light through the absorber. Both effects result in an enhancement of the short-circuit current density.

Most hole transport layers (HTLs) used in perovskite solar cells (PSCs) require extrinsic doping to enhance conductivity and modify energy levels. However, such doping often induces structural disorder, compositional inhomogeneity, and band edge distortion owing to dopant segregation, reducing hole mobility and interfacial charge trapping. Herein, CoxSy with controlled stoichiometry is reported as a dopant‐free inorganic HTL. Three phase‐pure compositions, namely, CoS, Co4S3, and Co9S8, are synthesized using a hot‐injection method by controlling the injection temperature of a sulfur‐oleylamine precursor. Each stoichiometrically defined CoxSy HTL possessed distinct valence band positions, enabling systematic control of band alignment with that of the perovskite layer. PSCs containing these HTLs exhibited power conversion efficiencies (PCEs) of up to 18.65% and open‐circuit voltages of up to 1.09 V. To further enhance hole transport and charge collection efficiency, a bilayer HTL composed of CoxSy and 2,2′,7,7′‐tetrakis[N,N‐di(4‐methoxyphenyl)amino]‐9,9′‐spirobifluorene (spiro‐OMeTAD) is introduced. The PSC containing a Co4S3/spiro‐OMeTAD bilayer HTL exhibited a PCE of 24.41%. Moreover, the thermal and operational stabilities of the PSCs containing the CoxSy HTLs are better than those of the PSCs employing conventional spiro‐OMeTAD‐only HTLs. This strategy can expand the utility of previously underutilized nonstoichiometric materials as functional HTLs in high‐photovoltaic‐performance PSCs.

Indoor photovoltaics (IPV) has recently emerged as a sustainable and reliable energy technology to power the rapidly growing Internet of Things. Among various solar cell technologies, emerging perovskite solar cells (PSCs) have gained great interest for IPV; owing to their unique optoelectronic properties such as bandgap tunability to efficiently harvest the indoor light spectrum. The choice of hole transport layer (HTL) is critical for efficient PSCs, particularly in IPV applications to reduce the parasitic absorption losses in the indoor light spectrum. Here, we explore the potential of CuSCN to be used as a HTL for PSCs in IPV applications. We show that CuSCN-based PSC exhibits remarkable power conversion efficiency (η) as compared to PSCs using conventional PEDOT:PSS as HTL. We explore the effects of wavelength (λ) of incident photons and various design parameters of PSC for optimal cell operations. We show that at a particular perovskite thickness, CuSCN-based PSC exhibits ∼8%–12% higher η than that for PEDOT-based PSC, for all λ in the visible range of the spectrum. We further explore the effect of HTL doping/thickness on PSC performance and show that CuSCN-based PSC performs optimally for a wide range of doping/thickness of HTL. We also find that CuSCN-based PSC outperforms PEDOT-based PSC for a broad range of incident irradiance. Finally, we show that for large values of λ (i.e. λ = 700 nm), η exceeds 30%, close to the highest ever in the past work. The work presented in this study will provide guidance for the development of efficient PSCs for indoor applications.