Efficient Electron Transport Layer Research Articles

Design and simulation of Sb2S3 solar cells based on monolayer graphene as electron transport layer

In Sb2S3 solar cells, the p-n junction are generally formed by combination of p-type Sb2S3 absorber layer and n-type materials, such as CdS and TiO2. In this study, the design and simulation of the Sb2S3 solar cells with graphene as electron transport layer were performed. The device performance parameters with respect to the electron affinity of monolayer graphene, the doping concentration, thickness and bulk defect density of Sb2S3 layer were examined and optimized. The simulation results revealed that the performance of Sb2S3 solar cells could be improved by using a monolayer graphene with lower value of electron affinity. The optimum doping concentration of Sb2S3 absorber layer was found to be 1017 cm−3. Also, the optimum Sb2S3 absorber layer thickness was found to be 0.7 μm when the bulk defect density and the corresponding carrier diffusion length were 1015 cm−3 and 1.6 μm, respectively. According to the optimum values of different variables, the conversion efficiency of the Sb2S3 solar cells could be achieved as high as 23.30%. These results showed that the monolayer graphene could be served as an efficient and inexpensive electron transport layer.

Modulated growth of high-quality CsPbI3perovskite film using a molybdenum modified SnO2layer for highly efficient solar cells

High-quality β-CsPbI3film was grown using an efficient electron transport layer of low temperature Mo-doped SnO2nanocrystals. This work provides a simple strategy to simultaneously modulate CsPbI3perovskite growth and the interfaces in devices.

Comprehensive Electrical modeling analysis of Heterojunction Perovskite Solar Cells by using different electron transport nanostructured layers

Abstract A Comprehensive Electrical modeling analysis of Heterojunction Perovskite Solar Cells by using different nanostructures Electron transport layers is accomplished. COMSOL Multiphysics commercial package was used to design and analyze an optoelectronic model of different device structures of the electron transport layers of Perovskite Solar Cell; mainly single layer, bi-layer, and sandwich structures. This was achieved by investigating three metal oxide materials namely: ZnO, TiO2, and WO3. The results show an enhancement in the device performance by using the sandwich structure of TiO2/ZnO/TiO2 at thicknesses of (10/50/20) nm with a power conversion efficiency of 19.26%. While the study revealed that the least efficient electron transport layer is a single tungsten oxide layer at a thickness ~10 nm) with a power conversion efficiency of 12.14%.

Highly efficient inverted polymer solar cells by using solution processed MgO/ZnO composite interfacial layers

A highly efficient inverted polymer solar cell (PSC) has been successfully demonstrated by utilizing a wide bandgap magnesium oxide (MgO) film and ZnO stacked structure as an effective cathode interfacial layer. The MgO/ZnO bilayer structure is designed to combine the superiorities of both ZnO ETL and MgO film, based on the efficiency comparison of the PSCs without and with MgO interlayer. The ZnO film can serve as an efficient electron transport layer (ETL), while the MgO layer can reduce the surface defects of FTO and block the holes effectively, leading to an elevated electron collection and suppressed carrier recombination at the interface. With the excellent dual functions interface characteristics induced by the MgO/ZnO stacked films, the corresponding inverted PSC device based on the PTB7-Th:PC71BM photoactive layer system presents a superior power conversion efficiency (PCE) of 11.02%, which is higher than that of the PSC without MgO (8.79%). We believe that the MgO/ZnO bilayer structure is a superior interfacial contender for the organic photovoltaics and other photoelectric devices requiring cathode interfacial layers.

Achieving High-Performance Perovskite Photovoltaic by Morphology Engineering of Low-Temperature Processed Zn-Doped TiO2 Electron Transport Layer.

Perovskite solar cells (PSCs) have become one of the most promising renewable energy converting devices. However, in order to reach a sufficiently high power conversion efficiency (PCE), the PSCs typically require a high-temperature sintering process to prepare mesostructured TiO2 as an efficient electron transport layer (ETL), which prohibits the PSCs from commercialization in the future. This work investigates a low-temperature synthesis of TiO2 nanocrystals and introduces a two-fluid spray coating process to produce a nanostructured ETL for the following deposition of perovskite layer. The temperature during the whole deposition process can be maintained under 150 °C. Compared to the typical planar TiO2 layer, the perovskite layer fabricated on a nanostructured TiO2 layer shows uniform compactness, preferred orientation, and high crystallinity, leading to reproducible and promising device performance. The detail mechanisms are revealed by the contact angle test, morphology characterization, grazing incident wide angle X-Ray scattering measurement, and space charge limited currents analysis. Finally, optimized device performance can be achieved through adequate Zn doping in the TiO2 layer, demonstrating an average PCE of 19.87% with champion PCE of 21.36%. The efficiency can maintain over 80% of its original value after 3000 h storage in ambient atmosphere. This study suggests a promising approach to offer high-efficiency PSCs using the low-temperature process.

A Highly Conductive Titanium Oxynitride Electron-Selective Contact for Efficient Photovoltaic Devices.

High-quality carrier-selective contacts with suitable electronic properties are a prerequisite for photovoltaic devices with high power conversion efficiency (PCE). In this work, an efficient electron-selective contact, titanium oxynitride (TiOx Ny ), is developed for crystalline silicon (c-Si) and organic photovoltaic devices. Atomic-layer-deposited TiOx Ny is demonstrated to be highly conductive with a proper work function (4.3eV) and a wide bandgap (3.4eV). Thin TiOx Ny films simultaneously provide a moderate surface passivation and enable a low contact resistivity on c-Si surfaces. By implementation of an optimal TiOx Ny -based contact, a state-of-the-art PCE of 22.3% is achieved for a c-Si solar cell featuring a full-area dopant-free electron-selective contact. Simultaneously, conductive TiOx Ny is proven to be an efficient electron-transport layer for organic photovoltaic (OPV) devices. A remarkably high PCE of 17.02% is achieved for an OPV device with an electron-transport TiOx Ny layer, which is superior to conventional ZnO-based devices with a PCE of 16.10%. Atomic-layer-deposited TiOx Ny ETL on a large area with a high uniformity may help accelerate the commercialization of emerging solar technologies.

Well-ordered vertically aligned ZnO nanorods arrays for high-performance perovskite solar cells

ZnO as a typical wide bandgap n-type semiconductor has been broadly employed as an electron transport layer in perovskite solar cells. In this work, we proposed a mesoporous scaffold constructed of vertically aligned ZnO nanorods through a low-temperature water bath. By precisely adjusting the reaction time, well-ordered ZnO nanorods were grown on FTO substrate with different lengths. Taking advantage of the highly visible transmittance, enhanced contact area, shortened electron transport route and compact integrated interface, high-performance mesoporous perovskite solar cells (PSCs) were fabricated. The optimum length of ZnO nanorod based PSC yielded a power conversion efficiency of 14.22% under AM 1.5G illumination. This research suggests that ZnO nanorods with appropriate length are an efficient electron transport layer in mesoporous perovskite solar cells.

Hybrid interfacial ETL engineering using PCBM-SnS2 for High-Performance p-i-n structured planar perovskite solar cells

Fullerene derivatives, such as PCBM i.e. [6,6]-phenyl C61 butyric acid methyl ester, are actively used as electron-transport layers (ETL) in inverted perovskite solar cells (PSC). However, limitations, such as low electron transportation, large electron trap region, poor film formation, and profuse non-radiative recombination, at the perovskite/PCBM interface result in relatively low performance in inverted PSC. Herein, a significant strategy to overcome these challenges was envisaged via using tin disulphide (SnS2) combined with PCBM, forming a uniform mixture of PCBM-SnS2 with high electron transportation and favorable energy levels. In addition, the greater relative permittivity of SnS2 permits shrinkage in critical electron captured radius from 0.62 nm to 0.22 nm, thus reducing leakage current and non-radiative recombination at the perovskite/PCBM-SnS2 interface. The efficiency of PCBM-SnS2 ETL based inverted PSC reached up to approximately 20% having a high 82% fill factor along with improved internal and external quantum efficiencies. The PCBM-SnS2 ETL reduced the charge transportation resistance and increased recombination resistance. The device stability was improved due to increased hydrophobicity and electrical compactness of the PCBM-SnS2. Hence, the synergetic effect of PCBM-SnS2 as an efficient ETL has great potential in improving the performance of planar inverted PSC.

Study on spray-pyrolyzed In2S3 thin films, targeted as electron transport layer in solar energy

Efficient electron transport layers (ETLs) play a pivotal role in the performance of solar cells. In recent years, Indium sulfide (In2S3) has been studied as a promising ETL in CuInGaS(e)2, Cu2ZnSnS(e)4, and perovskite solar cells. Despite several studies on spray-deposited In2S3, there is no complete experimental investigation on In2S3 thin films. The effect of the molar ratio of S/In and the type of indium precursor on the structural, morphological, optical, and electrical properties of sprayed-In2S3 layers has been studied. Films were characterized using x-ray diffraction, scanning electron microscopy (SEM), optical transmission (UV-Vis), Mott–Schottky analysis, four-point probe, and cyclic voltammetry measurements. The crystallinity and morphological characteristics are strongly influenced by the type of indium salt, where indium acetate precursor results in a highly porous film compared with nitrate and chloride precursors. The chloride precursor demonstrates better crystallinity and considerably lower sheet resistance. All films are n-type with a carrier concentration in the range of ∼2 × 1017 to ∼2 × 1018 cm − 3, with an indirect bandgap of 2.0 eV.

RbF modified FTO electrode enable energy-level matching for efficient electron transport layer-free perovskite solar cells

The development of highly efficient electron transport layer free perovskite solar cells (ETL-free PSCs) with simplified and economical device configurations can significantly motivate the commercialization of PSCs. However, the performance of ETL-free PSCs has been hampered by the sluggish charge extraction and severe charge carrier recombination due to the energy-level mismatch at the interface of the perovskite and the transparent conductive electrode FTO (fluorine doped tin-oxide). In this study, this issue is well solved by modifying the FTO surface with a simple, low-cost and non-toxic rubidium fluoride (RbF) interlayer. An interfacial dipole layer is formed on the FTO surface by inserting a RbF layer, which tunes the work function of FTO, eliminates the electron transport barrier and optimizes the energy-level alignment at the FTO/perovskite interface, thereby enhancing the charge transfer and suppressing the carrier recombination. Consequently, the rigid ETL-free PSCs with RbF layer yield high efficiencies of up to 18.79%, higher than that of ETL-free devices on bare FTO (16.03%). By virtue of the low-temperature processability, a superior PCE of 15.7% has been achieved by flexible ETL-free PSCs fabricated on RbF modified plastic substrate. This study provides a simple, efficient and environmentally friendly approach to modify the FTO electrode for fabricating ETL-free PSCs, which contribute to promote the design of advanced interface materials for simplified and high-performance perovskite photovoltaics.

Simple route to interconnected, hierarchically structured, porous Zn2SnO4 nanospheres as electron transport layer for efficient perovskite solar cells

Constructing electron transport layer (ETL) with higher carrier mobility and suitable bandgap is of key importance as it greatly influences the photovoltaic performance of perovskite solar cells (PSCs). Zn2SnO4 (ZTO) carries a high electron mobility of 10–30 cm2 V−1 s−1, an order of magnitude over the widely used TiO2 ETL in PSCs, rendering it an excellent alternative to TiO2 ETL. Herein, we report a simple yet robust polymer-templating route to interconnected, hierarchically structured, porous ZTO nanospheres as an efficient ETL for high-performance organolead halide PSCs. The porous ZTO nanospheres ETL, composed of an assembly of 4.5-nm ZTO nanoparticles on the surface of porous nanosphere possessing 80–100 nm cavity, renders markedly improved light absorption, enhanced electron extraction, facilitated charger transportation, and suppressed carrier recombination in the resulting PSCs, which exhibit a power conversion efficiency (PCE) of 17.14%, greatly outperforming the device based on the ZTO nanoparticles (14.02%; i.e., without porosity). As such, the strategy for crafting porous yet hierarchically structured semiconductors with high carrier mobility may open up an avenue to create robust ETL, and by extension, hole transport layer (HTL) for high-performance optoelectronics.

The role of GQDs additive in TiO2 nanorods as an electron transfer layer on performance improvement of the perovskite solar cells

The electron transport layer (ETL) plays an important role in improving the performance of the perovskite solar cells (PSCs). The main focus is on different types of TiO2 structures as an efficient ETL. In the present work, TiO2 nanorods (NRs) are prepared by a simple one-step hydrothermal method and employ as an ETL in PSCs. The power conversion efficiency (PCE) of the TiO2 NRs based PSCs is improved about 217% compared with the mesoporous (mp) TiO2 based cells. In order to further enhance PCE of the PSCs, a new approach is adopted to synthesize the graphene quantum dots- TiO2 NRs (GQDs- TiO2 NRs) by hydrothermal method. The PCE of PSCs based on GQDs- TiO2 NRs show improvement of 1.34 times compared to the TiO2 NRs. The GQDs- TiO2 NRs is capable of being a promising alternative to be employed as an efficient electron transport materials for photovoltaic devices.

Tailoring C60 for Efficient Inorganic CsPbI2 Br Perovskite Solar Cells and Modules.

Although inorganic perovskite solar cells (PSCs) are promising in thermal stability, their large open-circuit voltage (VOC ) deficit and difficulty in large-area preparation still limit their development toward commercialization. The present work tailors C60 via a codoping strategy to construct an efficient electron-transporting layer (ETL), leading to a significant improvement in VOC of the inverted inorganic CsPbI2 Br PSC. Specifically, tris(pentafluorophenyl)borane (TPFPB) is introduced as a dopant to lower the lowest unoccupied molecular orbital (LUMO) level of the C60 layer by forming a Lewis acidic adduct. The enlarged free energy difference provides a favorable enhancement in electron injection and thereby reduces charge recombination. Subsequently, a nonhygroscopic lithium salt (LiClO4 ) is added to increase electron mobility and conductivity of the film, leading to a reduction in the device hysteresis and facilitating the fabrication of a large-area device. Finally, the as-optimized inorganic CsPbI2 Br PSCs gain a champion power conversion efficiency (PCE) of 15.19%, with a stabilized power output (SPO) of 14.21% (0.09 cm2 ). More importantly, this work also demonstrates a record PCE of 14.44% for large-area inorganic CsPbI2 Br PSCs (1.0 cm2 ) and reports the first inorganic perovskite solar module with the excellent efficiency exceeding 12% (10.92 cm2 ) by a self-developed quasi-curved heating method.

Successively Regioselective Electrosynthesis and Electron Transport Property of Stable Multiply Functionalized [60]Fullerene Derivatives.

With the recent advance in chemical modification of fullerenes, electrosynthesis has demonstrated increasing importance in regioselective synthesis of novel fullerene derivatives. Herein, we report successively regioselective synthesis of stable tetra- and hexafunctionalized [60]fullerene derivatives. The cycloaddition reaction of the electrochemically generated dianions from [60]fulleroindolines with phthaloyl chloride regioselectively affords 1,2,4,17-functionalized [60]fullerene derivatives with two attached ketone groups and a unique addition pattern, where the heterocycle is rearranged to a [5,6]-junction and the carbocycle is fused to an adjacent [6,6]-junction. This addition pattern is in sharp contrast with that of the previously reported biscycloadducts, where both cycles are appended to [6,6]-junctions. The obtained tetrafunctionalized compounds can be successively manipulated to 1,2,3,4,9,10-functionalized [60]fullerene derivatives with an intriguing “S”-shaped configuration via a novel electrochemical protonation. Importantly, the stability of tetrafunctionalized [60]fullerene products allows them to be applied in planar perovskite solar cells as efficient electron transport layers.

Solution processable small molecules as efficient electron transport layers in organic optoelectronic devices

The coated QPSMs form the interfacial dipole between the active layer and the cathode, which can induce the tuned WF of Al, leading to the enhanced electron transport in OSCs and OLEDs.

Imide-functionalized acceptor–acceptor copolymers as efficient electron transport layers for high-performance perovskite solar cells

Acceptor–acceptor type copolymers are developed as electron transport layers for perovskite solar cells achieving efficiency up to 20.8% with improved device stability.

Efficiency and Stability Enhancement of Fully Ambient Air Processed Perovskite Solar Cells Using TiO2 Paste with Tunable Pore Structure

AbstractCrystallization and nucleation of the perovskite layer in the mesoscopic perovskite solar cells (PSCs) depend on the nucleation sites of the electron transport layer (ETL). The porosity optimization of TiO2 film as an efficient ETL plays an important role in the performance improvement of PSCs. In the present study, nontoxic carbon spheres synthesized with uniform morphology and controllable size under hydrothermal conditions and used as a template to generate the tunable porous TiO2 films. Furthermore, the effect of porosity modification of TiO2 on the formation of perovskite films with large grain size is studied in an ambient atmosphere with humidity higher than 50%. The best TiO2 film is produced with carbon spheres 8 wt% (C8), which results in the formation of a pinhole‐free, and compact‐packed perovskite layer. The fully air processed PSC device with the ETL made of C8 film exhibits an efficiency of 16.66% with reduced hysteresis, which is much superior in performance compared to the standard cell (11.72%). It is believed that this porosity optimization of TiO2 layer is a simple practical strategy for improved stability of fully air processed efficient perovskite solar cells and usable for the fabrication of reproducible compact perovskite layers in uncontrolled laboratories.

Efficient PbSe Colloidal Quantum Dot Solar Cells Using SnO2 as a Buffer Layer.

PbSe colloidal quantum dots (CQDs) are widely used in solar cells because of their tunable band gap, solution processability, and efficient multiple exciton generation effect. The most efficient PbSe CQD solar cells use high-temperature-processed ZnO as the electron transport layer (ETL), limiting their applications in flexible photovoltaics. Currently, low-temperature solution-processed SnO2 has been demonstrated as an efficient ETL for high-efficient PbS CQD and perovskite solar cells because of less parasitic light absorption and higher electron mobility. Herein, we introduce low-temperature solution-processed SnO2 as ETL for PbSe CQD solar cells, and fabricate the PbSe CQD absorber layer with a one-step spin-coating method. The champion device with the structure of FTO (SnO2:F)/SnO2/PbSe-PbI2/PbS-EDT (1,2-ethanedithiol)/Au achieves a high open-circuit voltage of 577.1 mV, a short-circuit current density of 24.87 mA cm-2, a fill factor of 67%, and an impressive power conversion efficiency of 9.67%. Our results pave the way for the development of low-temperature flexible PbSe CQD solar cells.

N-type conjugated polymer as efficient electron transport layer for planar inverted perovskite solar cells with power conversion efficiency of 20.86%

Fullerene and its derivatives are commonly used as electron transport layers (ETLs) in inverted perovskite solar cells (PSCs), since they show suitable band alignment and good electron mobility. However, fullerene-based ETLs typically result in low open-circuit voltages due to the interfacial defects, and they also exhibit poor photochemical and thermal stability. Consequently, there is great interest in the development of novel ETLs for high-performance inverted PSCs. In this work, two n-type polymers PBTI and PDTzTI are utilized as ETL in inverted PSCs, which are based on bithiophene imide and thienylthiazole imide, respectively. Due to its high electron mobility, well matched energy level alignment together with the passivation of interfacial traps/defects, device with the PDTzTI ETL demonstrates a best power conversion efficiency of 20.86%, which outperform those with PBTI and PCBM ETLs. Owning to the highly hydrophobic properties as well as the mobile ion blocking capability of polymer, PDTzTI ETL based device also exhibits excellent long-term and operational device stability as compared with the PCBM one. Our results demonstrate that rational selection of ETLs has great impact on the device efficiency and stability in inverted planar PSCs and that novel n-type polymer might be ideal alternative ETL in inverted planar PSCs.

Red‐Carbon‐Quantum‐Dot‐Doped SnO2 Composite with Enhanced Electron Mobility for Efficient and Stable Perovskite Solar Cells

An efficient electron transport layer (ETL) plays a key role in promoting carrier separation and electron extraction in planar perovskite solar cells (PSCs). An effective composite ETL is fabricated using carboxylic-acid- and hydroxyl-rich red-carbon quantum dots (RCQs) to dope low-temperature solution-processed SnO2 , which dramatically increases its electron mobility by ≈20 times from 9.32 × 10-4 to 1.73 × 10-2 cm2 V-1 s-1 . The mobility achieved is one of the highest reported electron mobilities for modified SnO2 . Fabricated planar PSCs based on this novel SnO2 ETL demonstrate an outstanding improvement in efficiency from 19.15% for PSCs without RCQs up to 22.77% and have enhanced long-term stability against humidity, preserving over 95% of the initial efficiency after 1000 h under 40-60% humidity at 25 °C. These significant achievements are solely attributed to the excellent electron mobility of the novel ETL, which is also proven to help the passivation of traps/defects at the ETL/perovskite interface and to promote the formation of highly crystallized perovskite, with an enhanced phase purity and uniformity over a large area. These results demonstrate that inexpensive RCQs are simple but excellent additives for producing efficient ETLs in stable high-performance PSCs as well as other perovskite-based optoelectronics.