Unlocking the potential of transport layers in solar cells: a universal design principle for high efficiency despite high extraction barriers

Carrier Dynamics Engineering for High-Performance Electron-Transport-Layer-free Perovskite Photovoltaics

18 - Perovskite solar cells: A review of architecture, processing methods, and future prospects

Lead-free tin 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.

Nanoparticles made of metal sulfides as quantum dots (QDs) have been prepared as electron transporting, light harvesting, and/or stabilizing parts for solar cells to improve their photovoltaic performance and durability. (AgIn)xZn2(1-x)S2 with its band gap in the range from 1.8 eV to 2.2 eV [1,2] has attractive potentials as the light absorber and the fluorescent material [3-5]. It was also found that the annealing of (AgIn)xZn2(1-x)S2 film at 500 ˚C in air brought the improvement of charge mobilities up to around 6.0 cm2 V-1 s-1[1,6]. In this context, preparation and band gap tuning of (AgIn)xZn2(1-x)S2 QDs through mixing with ZnO or TiO2 as the electron transport layer for inorganic-organic hybrid solar cells or metal halide perovskite solar cells (PSCs) have been investigated. Monodispersed AgInS2 [viz. x = 0 in (AgIn)xZn2(1-x)S2] QDs with an average value of the diameter of 6.22 ± 0.79 nm were prepared according to the reported procedures [7]. The interplanar spacing of the QDs was 0.33 nm, which corresponds to (112) crystal planes of the tetragonal phase of AgInS2. Introduction of AgInS2 QDs into hybrid solar cells resulted in over doubled enhancement of the photocurrent generation from 400 nm to 450 nm and the improvement of power conversion efficiencies (PCEs) as twice as the device without AgInS2 QDs [8]. While PSCs have been attracting many researchers because of their outstanding photophysical properties for photovoltaic performance. Development of the electron (or hole) transport layer of planar PSCs is one of the most important keys to improve the photovoltaic performance and the stability. Accordingly, development of hole transport layers by using various conjugated polymers for PSCs have been reported [9]. TiO2 and TiO2 mixed with AgInS2 QDs as dual electron transport layers were also introduced in PSCs in order to improve the photovoltaic performance and the stability. To prepare a decent physical contact between the electron transport layer and the rough surface of fluorine doped tin oxide, convective deposition technique was adopted because it has previously been confirmed that this method is one of the effective solution-based coating methods to deposit some self-assembled monolayer of both micro- and nanoparticles [10]. It was found that the addition of AgInS2 into TiO2 reduced pinholes at the interspace of the grains of the TiO2, enhanced a rectification ratio of the planar PSCs and improved the efficiency of the electron extraction from the active layer of metal halide perovskite through the TiO2/TiO2:AgInS2 QDs electron transport layer. PCE of the device was increased from 16.3% to 17.5% by the TiO2/TiO2:AgInS2 QDs (1.6 mg mL-1) as dual electron transport layers. The device with the dual electron transport layers showed the improvement of the external quantum efficiency in the wavelength region from 300 nm to 750 nm as compared with that of the device with TiO2 single layer. This result probably caused by the enhancement of light harvesting by AgInS2 QDs and the enhancement of the charge transfer from the perovskite layer to the dual electron transport layers. The long-term stability of the PSCs with the dual electron transport layers was confirmed when 1.6 mg mL-1 of AgInS2 was added, which was followed by the encapsulation and improvement of the retained PCE after the storage of the device in air for 15 days from 11% to 34% was also observed. This result implies that the TiO2/TiO2:AgInS2 QDs as dual electron transport layers not only brought the improvement of photovoltaic performance but also the durability. [1] Akaki, Y.; Kurihara, S.; Shirahama, M.; Tsurugida, K.; Seto, S.; Kakeno, T.; Yoshino, K. J. Phys. Chem. Solids. 2005, 66, 1858-1861. [2] Liu, B.; Li, X.; Zhao, Q.; Ke, J.; Tadé, M.; Liu, S. Appl. Catal., B 2016, 185, 1-10. [3] Kim, J.-H.; Lee, K.-H.; Jo, D.-Y.; Lee, Y.; Hwang, J. Y.; Yang, H. Appl. Phys. Lett. 2014, 105, 133104. [4] Shen, T.; Bian, L.; Li, B.; Zheng, K.; Pullerits, T.; Tian, J. Appl. Phys. Lett. 2016, 108, 213901. [5] Jasieniak, J.; Califano, M.; Watkins, S. E. ACS Nano. 2011, 5, 5888-5902. [6] Akaki, Y.; Kurihara, S.; Shirahama, M.; Tsurugida, K.; Kakeno, T.; Yoshino, K. J Mater Sci: Mater Electron 2005, 16, 393-396. [7] Torimoto, T.; Adachi, T.; Okazaki, K.-i.; Sakuraoka, M.; Shibayama, T.; Ohtani, B.; Kudo, A.; Kuwabata, S. J. Am. Chem. Soc. 2007, 129, 12388-12389. [8] Kim, E.-M.; Ruankham, P.; Lee, J.-H.; Hachiya, K.; Sagawa, T. Jpn. J. Appl. Phys. 2016, 55, 02BF06. [9] Ruankham, P.; Sagawa, T. J Mater Sci: Mater Electron 2018, 29, 9058-9066. [10] Kaewprajak, A.; Kumnorkaew, P.; Sagawa, T. Org. Electron. 2018, 56, 16-26.

ABX3 Perovskites for Tandem Solar Cells

The perovskite exhibited outstanding performance and was a promising alternative material for a low-cost, high power conversion efficiency (PCE) solar cell application. To avoid the high-cost organic materials as electron transport layers (ETL) and hole transport layers (HTL) in perovskite solar cells (PSCs), here introduce the inorganic semiconductor nanomaterials ZnS and CuS work as an ETL and HTL, respectively. In this work, we selected chalcogenides such as zinc sulfide (ZnS) and copper sulfide (CuS) as the 2-electron and hole transport layers and utilized them for perovskite solar cell application. For the proposed cell structure FTO/ZnS/perovskite (CH3NH3PbI3)/CuS/Ag, the deposition of layers has been achieved via different techniques such as thermal evaporation, spin coating and doctor blade, respectively. X-ray diffraction and Field effect scanning electron microscopy (FESEM) with Energy-dispersive X-ray spectroscopy were used to characterize the structural and morphological properties of the prepared samples. UV-Visible spectrophotometer and current density-voltage curve were used to measure the optical and electrical parameters of the deposited layers, respectively. From the J-V characteristics, for the proposed and fabricated PSCs, the estimated PCE is about 0.28 %, open-circuit voltage (VOC) = 0.29 V, and short-circuit current density (JSC) = 3.96 mA/cm2. The results are good and the inorganic nanomaterial layers used in this study are promising for future studies. HIGHLIGHTS In this study, chalcogenide materials such as zinc sulphide (ZnS) as the electron transport layer and cadmium sulfide (CdS) as the hole transport layer in solar perovskite cell applications were investigated Use easy and simple deposit methods such as chemical bath deposition and doctor blade method The possibility of using chalcogenide materials in the field of perovskite solar cells, although the efficiency of the obtained cell is very small, is an indication of the response of such materials in the application of perovskite solar cells GRAPHICAL ABSTRACT

The CsPbBr3 perovskite exhibits strong environmental stability under light, humidity, temperature, and oxygen conditions. However, in all-inorganic perovskite solar cells (PSCs), interface defects between the carbon electrode and CsPbBr3 limit the carrier separation and transfer rates. We used black phosphorus (BP) nanosheets as the hole transport layer (HTL) to construct an all-inorganic carbon-based CsPbBr3 perovskite (FTO/c-TiO2/m-TiO2/CsPbBr3/BP/C) solar cell. BP can enhance hole extraction capabilities and reduce carrier recombination by adjusting the interface contact between the perovskite and the carbon layer. Due to the coordination of the energy structure related to interface charge extraction and transfer, BP, as a new type of hole transport layer for all-inorganic CsPbBr3 solar cells, achieves a power conversion efficiency (PCE) that is 1.43% higher than that of all-inorganic carbon-based CsPbBr3 perovskite solar cells without a hole transport layer, reaching 2.7% (Voc = 1.29 V, Jsc = 4.60 mA/cm2, FF = 48.58%). In contrast, the PCE of the all-inorganic carbon-based CsPbBr3 perovskite solar cells without a hole transport layer was only 1.27% (Voc = 1.22 V, Jsc = 2.65 mA/cm2, FF = 39.51%). The unencapsulated BP-based PSCs device maintained 69% of its initial efficiency after being placed in the air for 500 h. In contrast, the efficiency of the PSC without HTL significantly decreased to only 52% of its initial efficiency. This indicates that BP can effectively enhance the PCE and stability of PSCs, demonstrating its great potential as a hole transport material in all-inorganic perovskite solar cells. BP as the HTL for CsPbBr3 PSCs can passivate the perovskite interface, enhance the hole extraction capability, and improve the optoelectronic performance of the device. The subsequent doping and compounding of the BP hole transport layer can further enhance its photovoltaic conversion efficiency in PSCs.

Perovskite solar cells (PSCs) have emerged as a promising alternative to traditional silicon solar cells due to their low cost of fabrication and high power conversion efficiency (PCE). The utilization of lead halide perovskites as absorber layers in perovskite solar cells has been impeded by two major issues: lead poisoning and stability concerns. These hindrances have greatly impeded the industrialization of this cutting-edge technology. In light of the harmful effects of lead in perovskite solar cells, researchers have shifted their attention to exploring lead-free metal halide perovskites. However, the present alternatives to lead-based perovskite exhibit poor performance, thus prompting further inquiry into this matter. The primary objective of this research is to investigate the use of Cu2O as a hole transport layer in combination with lead-free metal halide perovskite (CsSn0.5Ge0.5I3) to achieve superior performance. Through meticulous experimentation, the suggested model has achieved outstanding results by optimizing several key variables. These variables include the thickness of the absorber layer (CsSn0.5Ge0.5I3), defect density, and doping densities, as well as the back contact work function and the operating temperature associated with each layer. The proposed FTO/PC60BM/CsSn0.5Ge0.5I3/Cu2O/Au solar cell structure surpassed prior configurations by comprehensively examining key aspects such as absorber layer thickness and defect density, doping densities, and back contact work. The structure has been also compared with multiple electron transport elements and concluded that the proposed model functions superior due to the use of PC60BM as an electron transport layer and it has an improved electron extraction procedure. Finally, the proposed model has achieved the optimized values as Jsc of 31.56 mA/cm-2, Voc of 1.12 V, FF of 81.47%, and PCE of 27.72%. As a consequence of this research, the investigated structure may be an excellent contender for the eventual creation of lead-free solar power cells made from perovskite.

A key to achieve high efficiency in solar cells is to have charge extraction layer with proper energy levels. This layer selectively extracts electrons (or holes) whilst blocking the hole (or electron) and therefore help in reducing the recombination at various interfaces. Conventionally, WO3 is used as a hole-transport and electron-blocking layer in perovskite and polymer solar cells owing to high work function and carrier mobility and excellent thermal stability. In this paper, we report preparation of crystalline ultra-thin WO3 films at low temperature and its application as electron-transport and hole blocking layer (BL). For this purpose, WO3-octadecyl amine (ODA) multilayers were prepared by Langmuir-Blodgett (LB) technique and decomposed by UV-ozone treatment. The films were annealed at different temperatures in order to improve the crystallinity. The conversion of WO3-ODA complex (WO3-ODA) in WO3 was confirmed from X-ray photoelectron spectroscopy (XPS), Fourier Transform infrared spectroscopy (FTIR) and Raman spectroscopy. Films were further characterized using electrochemical technique in order to assess their blocking properties. Excellent blocking behavior observed for prepared WO3 films suggest their suitability as BL in solar cell application. The WO3 films, when employed as BL in dye sensitized solar cells (DSSC), were found to improve efficiency as well as short-circuit current density (Jsc) and open-circuit potential (Voc) in comparison with DSSCs fabricated using conventionally prepared TiO2 BL. The analyses of obtained results suggest that the WO3 film prepared by LB technique can be a potential blocking layer for DSSC and perovskite solar cells.

Performance analysis of several electron/hole transport layers in thin film MAPbI3-based perovskite solar cells: A simulation study

Decoupling the effects of defects on efficiency and stability through phosphonates in stable halide perovskite solar cells

Perovskite materials have gained considerable attention in recent years for their potential to improve the efficiency of solar cells. This study focuses on optimizing the efficiency of perovskite solar cells (PSCs) by investigating the thickness of the methylammonium-free absorber layer in the device structure. In the study we used a SCAPS-1D simulator to analyze the performance of MASnI3 and CsPbI3-based PSCs under AM1.5 illumination. The simulation involved using Spiro-OMeTAD as a hole transport layer (HTL) and ZnO as the electron transport layer (ETL) in the PSC structure. The results indicate that optimizing the thickness of the absorber layer can significantly increase the efficiency of PSCs. The precise bandgap values of the materials were set to 1.3 eV and 1.7 eV. In the study we also investigated the maximum thicknesses of the HTL, MASnI3, CsPbI3, and the ETL for the device structures, which were determined to be 100 nm, 600 nm, 800 nm, and 100 nm, respectively. The improvement techniques used in this study resulted in a high power-conversion efficiency (PCE) of 22.86% due to a higher value of VOC for the CsPbI3-based PSC structure. The findings of this study demonstrate the potential of perovskite materials as absorber layers in solar cells. It also provides insights into improving the efficiency of PSCs, which is crucial for advancing the development of cost-effective and efficient solar energy systems. Overall, this study provides valuable information for the future development of more efficient solar cell technologies.

Two-dimensional materials are a new class of materials for energy applications because of their tunable bandgap, and economical and solution-processable nature. The power conversion efficiencies of organic and perovskite solar cells are increasing dramatically, owing to the utilization of various nanomaterials and large-scale fabrication processes. Hence, utilization of 2D materials in organic and perovskite solar cells is an advantageous option due to their tunable electronic structure, high mobility, and high optical transparency. In order to further increase the power conversion efficiency, 2D nanomaterials could be applied as hole (HTL) and electron transport layers (ETL) for organic and perovskite solar cells. The tunable band structure and the enhanced charge transfer mechanism in 2D nanomaterials could boost the performance of the solar cell. Hence, this chapter focuses on integration of 2D nanomaterials, such as graphene, transition metal dichalcogenides, and MXenes, in organic and perovskite solar cells, as HTLs or ETLs. The fundamental processes as well as stability and lifetime of 2D nanomaterials incorporated in solar cells are also discussed. Furthermore, the chapter highlights recent advances and the future potential of 2D nanomaterial-based solar cells towards high performance, flexibility, and high stability.

Compared to conventional silicon solar cells, perovskite solar cells (PSCs) provide a number of advantages, including a high power conversion efficiency (PCE) and affordable manufacturing expenses. Lead poisoning and stability concerns have been the main challenge to use lead halide perovskites as absorber layers in perovskite solar cells. These obstacles have made it much more difficult to industrialize this state-of-the-art technology. Researchers are now focusing on lead-free metal halide perovskites due to the negative impacts of lead in perovskite solar cells. In demand to explore the physical properties and efficiency of perovskites, as well as their working principle, a comprehensive study of both the material and device is required. Therefore the WEIN2k and SCAPS-1D tools are employed to explore the structural, electronic and optical properties along with the solar cell efficiency of halide Cs2TMGaCl6 (TM = Cu, Ag) perovskites. The reported findings of structural properties are aligned with experiments. The electronic properties of Cs2TMGaCl6 (TM = Cu, Ag) compounds reveal the direct bandgap and visible light semiconducting nature make them ideal for optoelectronic devices and solar cell applications. To model the efficiency of these compounds based solar cells, WS2 and TiO2-SnO2 as electron transport layer (ETL), different type of hole transport layer (HTL) and Cs2TMGaCl6 (TM = Cu, Ag) as the absorber layer is used. The most efficient solar cell is the FTO/WS2/Cs2TMGaCl6 (TM = Cu, Ag)/CBTS/Cu, which achieved Jsc values of 15.32 and 12.30 mA cm−2, Voc values of 1.44 and 1.13 V, FF values of 81.08 and 79.39%, and PCE values of 14.14 and 14.08% respectively upon consequence of radiative recombination coefficients. This finding facilitates future studies aimed at developing fully inorganic perovskite photovoltaics lacking of lead halide, demonstrating improved photovoltaic performance.