Efficient Electron Transport Layer Research Articles

Bowl-Assisted Ball Assembly for Solvent-Processing the C60 Electron Transport Layer of High-Performance Inverted Perovskite Solar Cell.

Pristine fullerene C60 is an excellent electron transport material for state-of-the-art inverted structure perovskite solar cells (PSCs), but its low solubility leaves thermal evaporation as the only method for depositing it into a high-quality electron transport layer (ETL). To address this problem, we herein introduce a highly soluble bowl-shaped additive, corannulene, to assist in C60 -assembly into a smooth and compact film through the favorable bowl-ball interaction. Our results show that not only corannulene can dramatically enhance the film formability of C60 , it also plays a critical role in forming C60 -corannulene (CC) supramolecular species and in boosting intermolecular electron transport dynamics in the ETL. This strategy has allowed CC devices to deliver high power conversion efficiencies up to 21.69 %, which is the highest value among the PSCs based on the solution-processed-C60 (SP-C60 ) ETL. Moreover, the stability of the CC device is far superior to that of the C60 -only device because corannulene can retard and curb the spontaneous aggregation of C60 . This work establishes the bowl-assisted ball assembly strategy for developing low-cost and efficient SP-C60 ETLs with high promise for fully-SP PSCs.

Tailoring defects in electron transporting Zn2SnO4 layers by multilayer engineering and Cr doping towards efficient and stable carbon-based perovskite solar cells

The quality of the electron transporting layer (ETL) is crucial for perovskite solar cell (PSC) performance and stability. Defects in the ETL can cause charge recombination losses and device instability. Herein, crystalline chromium-doped zinc stannate (Cr-doped Zn2SnO4) nanoparticles bilayered with a compact zinc tin oxide (c-ZTO) are proposed as an efficient ETL in PSCs. It was found that Cr incorporation improved the quality of the ZTO crystal by inducing more crystal lattice oxygen, reducing the surface defects, and narrowing the particle size distribution. A perovskite film with larger grains was achieved on the Cr-doped ZTO film. The best PSC showed power conversion efficiency (PCE) of 15.32% and a reduction in the device hysteresis effect. The PSC based on Cr-doped ZTO exhibited superior thermal and UV light stability compared to the conventional single c-ZTO PSC. The main improvement in device performance and device stability was attributed to the suppression of defect trap density. Additionally, the colloidal Cr-doped ZTO solution could be reused for at least 10 months, making it suitable for industrial PSC manufacturing due to the negligible solution aging effect. Our bilayered c-ZTO/Cr-ZTO nanoparticles provide a high quality ETL, offering great potential for efficient and stable PSCs.

Nitrogen-Doped Graphene Quantum Dot–Tin Dioxide Nanocomposite Ultrathin Films as Efficient Electron Transport Layers for Planar Perovskite Solar Cells

Tin dioxide (SnO2) has recently been recognized as an excellent electron transport layer (ETL) for perovskite solar cells (PSCs) due to its advantageous properties, such as its high electron mobility, suitable energy band alignment, simple low-temperature process, and good chemical stability. In this work, nitrogen-doped graphene quantum dots (N-GQDs) were prepared using a hydrothermal method and then used to fabricate N-GQD:SnO2 nanocomposite ultrathin films. N-GQD:SnO2 nanocomposite ultrathin films were investigated and applied as electron transport layers in planar PSCs. The presence of N-GQDs with an average size of 6.2 nm in the nanocomposite improved its morphology and reduced surface defects. The excitation–emission contour map indicated that the N-GQDs exhibited a remarkably enhanced light-harvesting capability due to the possibility of absorbing UV light and producing emissions in the visible range. The quenching of photoluminescence spectra showed that the N-GQDs in nanocomposite ultrathin films improved electron extraction and reduced charge recombination. As a result, the power conversion efficiency (PCE) of our planar PSCs fabricated with the optimized N-GQD:SnO2 nanocomposite electron transport layer was improved by 20.4% over pristine SnO2-based devices.

Moderate temperature deposition of RF magnetron sputtered SnO2-based electron transporting layer for triple cation perovskite solar cells

The perovskite solar cells (PSCs) are still facing the two main challenges of stability and scalability to meet the requirements for their potential commercialization. Therefore, developing a uniform, efficient, high quality and cost-effective electron transport layer (ETL) thin film to achieve a stable PSC is one of the key factors to address these main issues. Magnetron sputtering deposition has been widely used for its high quality thin film deposition as well as its ability to deposit films uniformly on large area at the industrial scale. In this work, we report on the composition, structural, chemical state, and electronic properties of moderate temperature radio frequency (RF) sputtered SnO2. Ar and O2 are employed as plasma-sputtering and reactive gases, respectively. We demonstrate the possibility to grow a high quality and stable SnO2 thin films with high transport properties by reactive RF magnetron sputtering. Our findings show that PSC devices based on the sputtered SnO2 ETL have reached a power conversion efficiency up to 17.10% and an average operational lifetime over 200 h. These uniform sputtered SnO2 thin films with improved characteristics are promising for large photovoltaic modules and advanced optoelectronic devices.

Doped/Undoped A1‐A2 Typed Copolymers as ETLs for Highly Efficient Organic Solar Cells

AbstractThe electron transport layer (ETL) is a critical component in achieving high device performance and stability in organic solar cells. Conjugated polyelectrolytes (CPEs) have become an attractive alternative due to film‐forming properties and ease of preparation. However, p‐type CPEs generally exhibit poor charge mobility and conductivity, incorporation of electron‐withdrawing units forming alternated D‐A conjugated backbone can make up for these deficiencies. Herein, the ratio of electron withdrawing moieties are further increased and two poly(A1‐alt‐A2) typed PIIDNDI‐Br and PDPPNDI‐Br based on the combination of naphthalene diimide (NDI) with isoindigo (IID) or diketopyrrolopyrrole (DPP) via direct arylation polycondensation are synthesized. These CPEs possess excellent alcohol solubility, a suitable lowest unocuppied molecular orbital energy level, and work function tunability. Surprisingly, the incorporation of IID and DPP units generate distinct self‐doping behaviors, which are confirmed by UV–vis absorption and ESR spectra. However, no matter doped or undoped, both CPEs present better charge‐transporting properties and conductivity when utilized as ETLs. The PIIDNDI‐Br and PDPPNDI‐Br display good universal compatibility with the blend of PM6:Y6 and PM6:L8‐BO, and PCEs of 18.32% and 18.36% are obtained, respectively, which also present excellent storage stability. In short, the combination of two different acceptors demonstrates an efficient strategy to design highly efficient ETLs for high performance photovoltaic devices.

New Insights into Interfacial Passivation on 3D Graphene–CuInS2 Composites‐Based Perovskite Solar Cells

Although it is generally accepted by the perovskite solar cells community that their interface behaviors have a profound impact on their power conversion efficiency (PCE) and stability, such interfacial engineering on the bottom interface between electron transport layer (ETL) and perovskite film is still lagging. Herein, a 3D graphene (G)–CuInS2 composite is designed as an efficient ETL to improve both the interfacial contact and passivate defects at the G–CuInS2/perovskite interface. The lattice matching of graphene and methylammonium lead iodide CH3NH3PbI3 inhibits the concentrated stress generated during the growth of perovskite, resulting in crystal films with large grain boundaries. The low‐electron defect density in 3D G–CuInS2 composite facilitates the electron transport from perovskite film to CuInS2 quantum dots. In addition, 3D G–CuInS2 shows excellent carrier extraction capability of reducing carrier extraction time by 1.47 times than that of the counterpart. Correspondingly, a highly improved PCE of 22.4% is obtained, which increases by 15% of the counterpart. Furthermore, the unencapsulated device based on 3D G–CuInS2 shows long‐term stability, maintaining 85% of its original efficiency in air for 30 days. This strategy provides a new route to interfacial passivation engineering for preparation of high‐performance perovskite solar cells.

Round-comb Fe2O3@SnO2 heterostructures enable efficient light harvesting and charge extraction for high-performance all-inorganic perovskite solar cells

The precise design of an electron transport layer (ETL) to improve the light-harvesting and quality of perovskite (PVK) film plays a crucial role in the photovoltaic performance of n-i-p perovskite solar cells (PSCs). In this work, a novel three-dimensional (3D) round-comb Fe2O3@SnO2 heterostructure composites with high conductivity and electron mobility induced by its Type-II band alignment and matched lattice spacing is prepared and employed as an efficient mesoporous ETL for all-inorganic CsPbBr3 PSCs. Arising from the multiple light scattering sites provided by the 3D round-comb structure, the diffuse reflectance of Fe2O3@SnO2 composites is increased to improve the light absorption of the deposited PVK film. Besides, the mesoporous Fe2O3@SnO2 ETL affords not only more active surface for sufficient exposure to the CsPbBr3 precursor solution but also a wettable surface to reduce the barrier for heterogeneous nucleation, which realizes the regulated growth of a high-quality PVK film with less undesired defect. Hence, both the light-harvesting capability, the photoelectrons transport and extraction are improved, and the charge recombination is restrained, delivering an optimized power conversion efficiency (PCE) of 10.23 % with a high short-circuit current density of 7.88 mA cm−2 for the c-TiO2/Fe2O3@SnO2 ETL based all-inorganic CsPbBr3 PSCs. Moreover, under lasting erosion at 25 °C and 85 % RH for 30 days and light-soaking (AM 1.5G) for 480 h in air atmosphere, the unencapsulated-device shows superiorly persistent durability.

Spray-Deposited Aluminum-Doped Zinc Oxide as an Efficient Electron Transport Layer for Inverted Organic Solar Cells

Spray-deposited thin films of zinc oxide (ZnO) and aluminum-doped zinc oxide (Al-ZnO) are characterized in detail to get insight into the role of a dopant in the matrix. ZnO and Al-ZnO are implemented as electron transport layers (ETLs) in inverted organic solar cells (IOSCs) with PTB7-Th as a donor and IEICO-4F as a nonfullerene acceptor, forming the bulk heterojunction (BHJ) photoactive layer. Organic solar cells (OSCs) based on the ZnO ETL exhibit a short-circuit current density (JSC) of 24.46 mA/cm2 and an open-circuit voltage (VOC) of 0.68 V, yielding a power conversion efficiency (PCE) of 9.3%. A solar cell based on the Al-ZnO ETL yields a higher JSC of 25.16 mA/cm2 and a VOC of 0.71 V, resulting in a PCE of 10.5%, which indicates that Al doping improves the device performance. Time-delayed collection field (TDCF) measurements yielded field-independent charge generation for both devices. Furthermore, steady-state photoluminescence (PL), time-resolved PL, and transient absorption measurements confirm reduction in the number of defect states in Al-ZnO thin films compared to ZnO thin films and efficient charge transfer, yielding an overall improved IOSC device performance.

Low‐Temperature Synthesis of SnO2 Nanocrystals as Electron Transport Layers for High‐Efficiency CsPbI2Br Perovskite Solar Cells

Perovskite solar cells (PSCs) have recently become a hot topic in photovoltaics due to their high power conversion efficiency (PCE) and low‐cost processing. As a key component of PSCs, electron transport layers (ETLs) that play a vital role in efficient PSCs generally require high charge extraction ability, mobility, and easy fabrication. Herein, a simple route to obtain dispersion of tin oxide nanocrystals (SnO2 NCs) with uniform diameters and high stability as efficient ETLs for CsPbI2Br solar cells is demonstrated. The champion device achieves a remarkable PCE of 16.22% with an open‐circuit voltage of 1.30 V. This work offers a facile and effective way to fabricate high‐performance ETL nanocrystals in PSCs.

Efficient Tuning of the Opto-Electronic Properties of Sol-Gel-Synthesized Al-Doped Titania Nanoparticles for Perovskite Solar Cells and Functional Textiles.

The efficient electron transport layer (ETL) plays a critical role in the performance of perovskites solar cells (PSCs). Ideally, an unobstructed network with smooth channels for electron flow is required, which is lacking in the pristine TiO2-based ETL. As a potential solution, here we tuned the structure of TiO2 via optimized heteroatom doping of Al. Different concentrations (1, 2, and 3 wt%) of Al were doped in TiO2 and were successfully applied as an ETL in PSC using spin coating. A significant difference in the structural, opto-electronic, chemical, and electrical characteristics was observed in Al-doped TiO2 structures. The opto-electronic properties revealed that Al doping shifted the absorption spectra toward the visible range. Pure titania possesses a bandgap of 3.38 eV; however, after 1, 2, and 3% Al doping, the bandgap was linearly reduced to 3.29, 3.25, and 3.18 eV, respectively. In addition, higher light transmission was observed for Al-doped TiO2, which was due to the scattering effects of the interconnected porous morphology of doped-TiO2. Al-doped titania shows higher thermal stability and a 28% lower weight loss and can be operated at higher temperatures compared to undoped titania (weight loss 30%) due to the formation of stable states after Al doping. In addition, Al-doped TiO2 showed significantly high conductivity, which provides smooth paths for electron transport. Thanks to the effective tuning of band structure and morphology of Al-doped TiO2, a significant improvement in current densities, fill factor, and efficiency was observed in PSCs. The combined effect of better Jsc and FF renders higher efficiencies in Al-doped TiO2, as 1, 2, and 3% Al-doped TiO2 showed 12.5, 14.1, and 13.6% efficiency, respectively. Compared to undoped TiO2 with an efficiency of 10.3%, the optimized 2% Al doping increased the efficiency up to 14.1%. In addition, Al-doped TiO2 also showed improvements in antibacterial effects, required for photoactive textiles.

Spray-assisted deposition of a SnO2 electron transport bilayer for efficient inkjet-printed perovskite solar cells

A mesoporous SnO2-electron transport bilayer with a high surface-area-to-volume ratio is developed for application in inkjet-printed PSCs (IJP-PSCs). The use of SnO2-bilayer has uplifted the efficiency of IJP-PSCs up to a maximum of 16.9%.

Graphdiyne (CnH2n−2) coupled with ZnCo-MOF double S-scheme heterojunction forms an efficient electron transport layer and its characterizationvia in situXPS

The catalyst constructs double S-scheme heterojunctions. The excellent electrical conductivity of GDY and the synergistic effect of S-scheme heterojunctions promote the charge transfer and significantly improve the photocatalytic hydrogen evolution activity of GDY.

Achieving Small Temperature Coefficients in Carbon‐Based Perovskite Solar Cells by Enhancing Electron Extraction

AbstractHole transport layer (HTL)‐free carbon electrode‐based perovskite solar cells (C‐PSCs) have drawn great attention due to their excellent stability and simple fabrication process. However, the photovoltaic parameters of C‐PSCs usually exhibit large negative temperature coefficients (TCs). Herein, the TCs of C‐PSCs can be suppressed by enhancing electron extraction. An efficient electron transport layer (ETL), [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM)‐coated nanoneedle‐like brookite TiO2 (ND‐B‐TiO2) is used as ETL to prepare HTL‐free pure FAPbI3‐based C‐PSCs. Compared with bare ND‐B‐TiO2, PCBM@ND‐B‐TiO2 shows higher electron mobility, and better band alignment with formamidinium lead triiodide (FAPbI3) perovskite, as well as improved contact with perovskite, which leads to enhanced electron extraction and transportation. Consequently, the power conversion efficiency (PCE) of HTL‐free carbon‐based FAPbI3 PSC can reach up to 14.55%, which is one of the highest efficiencies for FAPbI3‐based planar C‐PSCs so far. More importantly, the optimized device is less sensitive to the operating temperature due to the boosted carrier extraction and passivated interface defects, showing a small TC(PCE) of only ≈−0.11%/°C between 25 °C and 85 °C. The work demonstrates that enhancing electron extraction is an effective way to achieve high‐performance C‐PSCs and high‐temperature solar cells.

Carrier Management via Integrating InP Quantum Dots into Electron Transport Layer for Efficient Perovskite Solar Cells

Metal oxides are the most efficient electron transport layers (ETLs) in perovskite solar cells (PSCs). However, issues related to the bulk (i.e., insufficient electron mobility, unfavorable energy level position) and interface of metal oxide/perovskite (detrimental surface hydroxyl groups) limit the transport kinetics of photoinduced electrons and prevent PSCs from unleashing their theoretical efficiency potential. Herein, the inorganic InP colloid quantum dots (CQDs) with outstanding electron mobility (4600 cm2 V-1 s-1) and carboxyl (-COOH) terminal ligands were uniformly distributed into the metal oxide ETL to form consecutive electron transport channels. The hybrid InP CQD-based ETL demonstrates a more N-type characteristic with more than 3-fold improvement in electron mobility. The formation of the Sn-O-In bond facilitates electron extraction due to suitable energy level alignment between the ETL and perovskite. The strong interaction between uncoordinated Pb2+ at the perovskite/ETL interface and the -COO- in the ligand of InP CQDs reduces the density of defects in perovskite. As a result, the hybrid InP CQD-based ETL with an optimized InP ratio (18 wt %) boosts the power conversion efficiency of PSCs from 22.38 to 24.09% (certified efficiency of 23.43%). Meanwhile, the device demonstrates significantly improved photostability and atmospheric storage stability.

High-Performance Deep Red Colloidal Quantum Well Light-Emitting Diodes Enabled by the Understanding of Charge Dynamics.

Colloidal quantum wells (CQWs) have emerged as a promising family of two-dimensional (2D) optoelectronic materials with outstanding properties, including ultranarrow luminescence emission, nearly unity quantum yield, and large extinction coefficient. However, the performance of CQWs-based light-emitting diodes (CQW-LEDs) is far from satisfactory, particularly for deep red emissions (≥660 nm). Herein, high efficiency, ultra-low-efficiency roll-off, high luminance, and extremely saturated deep red CQW-LEDs are reported. A key feature for the high performance is the understanding of charge dynamics achieved by introducing an efficient electron transport layer, ZnMgO, which enables balanced charge injection, reduced nonradiative channels, and smooth films. The CQW-LEDs based on (CdSe/CdS)@(CdS/CdZnS) ((core/crown)@(colloidal atomic layer deposition shell/hot injection shell)) show an external quantum efficiency of 9.89%, which is a record value for 2D nanocrystal LEDs with deep red emissions. The device also exhibits an ultra-low-efficiency roll-off and a high luminance of 3853 cd m-2. Additionally, an exceptional color purity with the CIE coordinates of (0.719, 0.278) is obtained, indicating that the color gamut covers 102% of the International Telecommunication Union Recommendation BT 2020 (Rec. 2020) standard in the CIE 1931 color space, which is the best for CQW-LEDs. Furthermore, an active-matrix CQW-LED pixel circuit is demonstrated. The findings imply that the understanding of charge dynamics not only enables high-performance CQW-LEDs and can be further applied to other kinds of nanocrystal LEDs but also is beneficial to the development of CQW-LEDs-based display technology and related integrated optoelectronics.

SnO2 modified mesoporous ZrO2 as efficient electron-transport layer for carbon-electrode based, low-temperature mesoscopic perovskite solar cells

SnO2 modified mesoporous ZrO2 is used to replace the mesoporous TiO2 layer and serves as a kind of mesoporous electron-transport layer during the low-temperature fabrication of mesoscopic perovskite solar cells that are based on carbon electrode. X-ray/ultraviolet photoelectron spectroscopy studies and electrical test observe that SnO2 modification brought down the work function while increasing the conductivity of the mesoporous ZrO2. Transient photovoltage/photocurrent decay curves, impedance spectroscopy, and photoluminescence mapping show that after the bottom layer of ZrO2 is modified by SnO2, the charge extraction process is accelerated while recombination is retarded. This modification helps to increase the power conversion efficiency from 4.70 (±0.85)% to 10.15 (±0.35)%, along with the optimized efficiency at 13.37% (AM1.5G, 100 mW/cm2) for the low-temperature devices. In addition, the effects of modification layers of SnO2 on the power conversion properties are carefully studied. This study shows that SnO2 modified mesoporous ZrO2 could serve as an efficient electron-transport layer for the low-temperature mesoscopic devices.

Solution-processed quantum dot SnO2 as an interfacial electron transporter for stable fully-air-fabricated metal-free perovskite solar cells

Perovskite solar cells could strongly compete with the silicon solar cells in the market soon as illustrated in recent studies. In this work, promising and stable metal-free perovskite solar cells (PSCs) has been successfully fabricated using an inorganic SnO2/Quantum dot SnO2 (QD-SnO2) double layer as an efficient electron transport layer via a low-temperature solution process. The fully-air fabricated PSCs in the form of FTO/SnO2/QD-SnO2/CH3NH3PbI3/Carbon were tested at different annealed QD-SnO2 between 300 and 500 °C. The as-prepared QD-SnO2 and the fabricated devices are characterized by various techniques, including XRD, XPS, HR-TEM, FE-SEM, UV–vis–NIR spectroscopy, PL, and solar simulator. The prepared QD-SnO2 at 300 °C has shown well-ordered nanoparticles of 5.6 nm in diameter with superior carrier density (1.5 × 1015 cm−3) and highest carrier mobility (64.1 cm2·V-1·s−1), accelerating the carriers separation process within the cell. The best devices demonstrated a maximum power conversion efficiency (PCE) of 11.7%, VOC 0.81 V, JSC 19.5 mA·cm−2, and FF 74%. The presence of an interfacial layer of QD-SnO2 over the blocking SnO2 upsurges the band gaps alignment and accelerates the carriers extraction rate affecting the performance of the fabricated perovskite devices. Moreover, the optimized fabricated devices revealed a shelf stability-life of four months in humid air (40%–50%) with >83% of its initial PCE. This simple synthetic approach can develop the opportunities to transfer the cell from the lab to the market, which will be compatible with large-scale production.

Ni-Doped SnO2 as an Electron Transport Layer by a Low-Temperature Process in Planar Perovskite Solar Cells.

Perovskite solar cells (PSCs) based on a planar structure have recently become more attractive due to their simple manufacturing process and relatively low cost, while most perovskite solar cells employ highly porous TiO2 as an electron transport layer in mesoporous devices offering higher energy conversion efficiency (PCE). In planar structural devices, non-radiative recombination effects of the absorber layer and the electron transport layer cause potential loss and lower PCE. We created an efficient electron transport layer by combining low-temperature Ni-doped SnO2 with SDBS as a surfactant (denoted as Ni:SnO2). Doping Ni+ into low-temperature solution-processed SnO2 increased the power conversion efficiency of PSCs from 17.8 to 19.7%.

P‐25: Student Poster: Solution‐Processed CH3NH3PbI3/ZnO Phototransistor with High Photodetectivity

We report a phototransistor using the CH3NH3PbI3/ZnO heterostructure. The CH3NH3PbI3 (MAPbI3) and ZnO are deposited via low‐cost solution process. MAPbI3 coated ZnO TFTs exhibited enhanced photocurrent upon exposure to white light. The heterostructure formed between perovskite and ZnO, works as an efficient electron transport layer. The device had a responsivity of 195 A/W and a high detectivity of 1.10 × 1013 Jones under white light. The high photo‐responsivity and detectivity resulted from the combination of suitable optoelectronic property of MAPbI3 films and the high mobility of the spray coated ZnO films.

Inside Front Cover: Volume 1 Issue 2

Interdisciplinary MaterialsVolume 1, Issue 2 p. ii-ii COVER IMAGEOpen Access Inside Front Cover: Volume 1 Issue 2 First published: 30 April 2022 https://doi.org/10.1002/idm2.12029AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract Inside Front Cover: Tin oxide is known as an efficient electron transport layer in perovskite solar cells (PSCs) due to its high transmittance, wide bandgap, and high electron mobility. In article number idm212021, Fuzhi Huang and co-workers develop high-quality tin oxide films via a nitrogen-doping strategy, the power conversion efficiency (PCE) and stability of devices have been improved significantly owing to the optimized interface of doped SnO2/perovskite. This simple scalable strategy has shown great promise toward highly efficient and stable PSCs. Volume1, Issue2April 2022Pages ii-ii RelatedInformation