Composite Electron Transport Layer Research Articles

Composites electron transport layer of PVA-regulated SnO2 for high-efficiency stable perovskite solar cells

As a new and efficient solar cell, perovskite solar cell has attracted wide attention due to its excellent performance. The electron transport layer in perovskite solar cells has a significant impact on device performance. SnO2 films that can be prepared by solution method have become the first choice for electron transport layer due to their simple process and excellent performance. However, the defects in SnO2 thin films and non-radiative recombination sites at the SnO2/Perovskite interface will lead to potential losses in the performance of photovoltaic devices. Therefore, in order to improve the interface loss and interface characteristics and prepare more efficient perovskite solar cells. In this work, a functional polymer, polyvinyl alcohol (PVA), is introduced to regulate the arrangement of SnO2 nanocrystals. The SnO2-PVA composite electron transport layer not only improves carrier transport, but also further affects the growth of perovskite films. PVA inhibits the agglomeration of tin dioxide particles by adding it to the aqueous solution of tin dioxide. Meanwhile, the oxygen vacancy defects in the SnO2 layer have also improved. Correspondingly, SnO2-PVA-based PSCs can be obtained a maximum efficiency of 23.73 %. Attributed to the strengthened interface binding and the improved perovskite crystallization process, the devices obtain good long-term stability, retaining 90 % of their initial performance after 1000 h operation at their maximum power point under 1 sun illumination.

Synergetic Optimization of Upper and Lower Surfaces of the SnO2 Electron Transport Layer for High-Performance n-i-p Perovskite Solar Cells.

The SnO2 electron transport layer (ETL) has been recognized as one of the most effective protocols for achieving high-efficiency perovskite solar cells (PSCs). To date, most research has primarily focused on the modification of the upper surface of SnO2 ETL films. The lower surface of the SnO2 film, which directly influences the film formation of solution-processed SnO2, is equally important but receives relatively less attention. Herein, we present a synergetic optimization approach involving the deposition of aluminum oxide (AlOx) via atomic layer deposition (ALD) as a buffer layer and the incorporation of rubidium acetate (RbAc) as an upper surface passivation additive. This process leads to a conformal coating of SnO2 nanoparticles, improved electrical performance, and higher-quality perovskite crystals. As a result, with this composite ETL film, the power conversion efficiency (PCE) reached 22.41 from 20.77%. Further modification with p-butyl iodide (BAI) on the perovskite upper surface increased the champion PCE to 23.32%, with a voltage loss of 0.41 V, ranking among the lowest values for the triple-cation mixed-halide perovskite absorber (1.58 eV). Importantly, the perovskite solar cells remained 87.30% of its initial performance after 14 days of aging and exhibited photostability under long-term UV (254 nm) illumination.

Improved UV stability of perovskite devices based on the synergistic effect of electron layer passivation engineering and component engineering

The electron transport layer is one of the key factors in constructing high-performance perovskite solar cells (PSCs). Pb2+ reduction induced by ultraviolet light can cause the generation of vacancies and defects, leading to the degradation of perovskite films and the reduction of PSCs performances. Ethylenediamine tetraacetic acid disodium salt (EDTA) is a chelating agent that can bind to Sn2+ divalent metal ions and hence change material properties. Herein, EDTA-SnO2/CeO2 composite electron transport layers were constructed to improve the ultraviolet light stability of PSCs. The oxygen defect in electron layers of tin dioxide could be passivated by the surface of EDTA; whilst rod-like CeO2 was used as a mesoporous electron transport layer and UV shielding agent, which can reflect UV light and prevent the absorption layer from being damaged. CeO2 has also a suitable band gap; this accelerates the charge extraction and transfer, suppresses the recombination of interfacial carriers. The experimental results showed that the ultraviolet light stability of PSCs was significantly improved. After continuous irradiation of ultraviolet light with energy of 80 mW/cm2 for 12 h, the unencapsulated device with CeO2 maintained nearly 90% the initial efficiency.

Enhanced Electron Transport and Mitigated Voltage Loss in Perovskite Photovoltaics Using Sb2O5@SnO2 Composite Electron Transport Layer.

The efficacy of electron transport layers (ETLs) is pivotal for optimizing the device performance of perovskite photovoltaic applications. However, colloidal dispersions of SnO2 are prone to aggregation and possess structural defects, such as terminal-hydroxyls (OHT) and oxygen vacancies (VOs), which can degrade the quality of ETLs, impede charge extraction and transport, and affect the nucleation and growth processes of the perovskite layer. In this study, the Sb(OH)4 - ions hydrolyzed from SbCl3 in colloidal dispersion can bind to defect sites and effectively stabilize the SnO2 nanocrystals are demonstrated. Upon oxidative annealing, a Sb2O5@SnO2 composite film is formed, in which the Sb2O5 not only mitigates the aforementioned defects but also broadens the energy range of unoccupied states through its dispersed conduction band. The increased electron affinity (EA) facilitates more efficient capture of photoexcited electrons from the perovskite layer, thus augmenting electron extraction and minimizing electron-hole recombination. As a result, a significant improvement in power conversion efficiency (PCE) from 22.60% to 24.54% is achieved, with an open circuit voltage (VOC) of up to 1.195V, along with excellent stability of unsealed devices under various conditions. This study provides valuable insights for the understanding and design of ETLs in perovskite photovoltaic applications.

An Efficient and Stable Inverted Structure Organic Solar Cell Using ZnO Modified by 2D ZrSe2 as a Composite Electron Transport Layer

AbstractAs an electron transport layer (ETL) widely used in organic solar cells (OSCs), ZnO has problems with energy level mismatch with the active layer and excessive defects on the ZnO surface, which can reduce the efficiency of OSCs. Here, ZnO/ZrSe2 composite is fabricated by modifying ZnO with 2D ZrSe2. The XPS and first‐principles calculation (FPC) show that ZnO obtains electrons from ZrSe2 and forms interfacial dipoles toward the active layer, which decreases the work function of ZnO, thus reducing the interface barrier and favoring the collection of electrons in OSCs. At the same time, after ZrSe2 modification, the oxygen vacancy density on the ZnO surface decreases, thus improving the conductivity of ZnO. More importantly, the femtosecond transient absorption (Fs‐TA) shows that ZrSe2 selectively traps holes from the active layer, which prevents the holes from entering the ZnO, thereby reducing the probability of electron recombination. Finally, ZnO/ZrSe2 composite is used as a novel ETL in OSCs with PBDB‐T: ITIC, PM6:Y6 and PM6: L8‐BO as active layers, and obtaining 12.09%, 16.34%, and 18.24% efficiency, respectively. This study provides a method for the interface modification of ZnO, and further investigates the role of 2D nanosheets in the interface modification.

Amorphous F‐doped TiOx Caulked SnO2 Electron Transport Layer for Flexible Perovskite Solar Cells with Efficiency Exceeding 22.5%

AbstractFlexible perovskite solar cells (f‐PSCs) show great promise in portable‐power applications (e.g., chargers, drones) and low‐cost, scalable productions (e.g., roll‐to‐roll). However, in conventional n–i–p architecture f‐PSCs, the low‐temperature processed metal oxide electron transport layers (ETLs) usually suffer from high resistance and severe defects that limit the power conversion efficiency (PCE) improvement of f‐PSCs. Besides the enhancement in the mobility of metal oxide and passivation for perovskite/ETL interfacial defects reported in previous literature, herein, the electron transport loss between the metal oxide nanocrystallines within the ETL is studied by introducing an amorphous F‐doped TiOx (F‐TiOx) caulked crystalline SnO2 composite ETL. The F‐TiOx in this novel composite ETL acts as an interstitial medium between adjacent SnO2 nanocrystallines, which can provide more electron transport channels, effectively passivate oxygen vacancies, and optimize the energy level arrangement, thus significantly enhancing the electron mobility of ETL and reducing the charge transport losses. The composite ETL‐based f‐PSCs achieve a high PCE of 22.70% and good operational stability. Furthermore, a moderate roughness of the composite ETL endows f‐PSCs with superior mechanical reliability by virtue of a strong coupling at the ETL/perovskite interface, by which the f‐PSCs can maintain 82.11% of their initial PCE after 4000 bending cycles.

MXene‐Regulated Perovskite Vertical Growth for High‐Performance Solar Cells

AbstractDefects at the interfaces of perovskite (PVK) thin films are the main factors responsible for instability and low photoelectric conversion efficiency (PCE) of PVK solar cells (PSCs). Here, a SnO2‐MXene composite electron transport layer (ETL) is used in PSCs to improve interfacial contact and passivate defects at the SnO2/perovskite interface. The introduced MXene regulates SnO2dispersion and induces a vertical growth of PVK. The lattice matching of MXene and perovskite suppresses the concentration of interfacial stress, thereby obtaining a perovskite film with low defects. Compared with SnO2‐based device, the PCE of SnO2‐MXene‐based device is improved by 15 % and its short‐circuit current is up to 25.07 mA cm−2. Furthermore, unencapsulated device maintained about 90 % of its initial efficiency even after 500 h of storage at 30–40 % relative humidity in ambient air. The composite ETL strategy provides a route to engineer interfacial passivation between metal halide perovskites and ETLs.

MXene-Regulated Perovskite Vertical Growth for High-Performance Solar Cells.

Defects at the interfaces of perovskite (PVK) thin films are the main factors responsible for instability and low photoelectric conversion efficiency (PCE) of PVK solar cells (PSCs). Here, a SnO2 -MXene composite electron transport layer (ETL) is used in PSCs to improve interfacial contact and passivate defects at the SnO2 /perovskite interface. The introduced MXene regulates SnO2 dispersion and induces a vertical growth of PVK. The lattice matching of MXene and perovskite suppresses the concentration of interfacial stress, thereby obtaining a perovskite film with low defects. Compared with SnO2 -based device, the PCE of SnO2 -MXene-based device is improved by 15 % and its short-circuit current is up to 25.07 mA cm-2 . Furthermore, unencapsulated device maintained about 90 % of its initial efficiency even after 500 h of storage at 30-40 % relative humidity in ambient air. The composite ETL strategy provides a route to engineer interfacial passivation between metal halide perovskites and ETLs.

Large improvement of photovoltaic performance of flexible perovskite solar cells using a multifunctional phospho-ethanolamine-modified SnO2 layer

The non-radiative recombination loss caused by diverse defects within SnO2 electron transport layer (ETL), perovskite film, and their interface greatly hinders the further improvement of the performance and stability of flexible perovskite solar cells (PSCs). Therefore, it is urgent to develop an effective strategy to address these issues. Herein, a multifunctional material, phospho-ethanolamine (PE), is introduced into SnO2 aqueous colloids to suppress defects and prepare high-quality ETL. The results demonstrate that the incorporation of PE can significantly reduce the number of Sn dangling bonds due to the formation of new Sn—O—P bonds, which is beneficial to ameliorating the electrical properties of SnO2 and obtaining dense SnO2 film. Meanwhile, the amino group (NH2) of PE can interact with uncoordinated Pb2+ in perovskite, thereby suppressing SnO2/perovskite interface defects and obtaining improved perovskite film quality. Consequently, the optimized flexible and rigid PSCs based on the SnO2-PE composite ETL yield outstanding photoelectric conversion efficiency (PCE) of 18.48% and 21.61%, respectively. Moreover, flexible PSCs based on SnO2-PE present excellent mechanical durability, and 90.6% of the original PCE is retained after 1000 bending cycles.

Biological/metal oxide composite transport layers cast from green solvents for boosting light harvesting response of organic photovoltaic cells indoors

Organic solar cells with biological/metal–oxide electron transport layers (ETLs), consisting of a ZnO compact layer covered by a thin DNA layer, both of which deposited with green solvents (water or water/alcohols mixtures) are presented for application under low intensity indoor lighting. Under white LED lamp (200, 400 lx), photovoltaic cells with P3HT:PC70BM polymer semiconductor blends delivered an average maximum power density (MPD) of 8.7 μW cm−2, corresponding to a power conversion efficiency, PCE, of = 8.56% (PCE of best cell was 8.74%). The ZnO/DNA bilayer boosted efficiency by 68% and 13% in relative terms compared to cells made with DNA-only and ZnO-only ETLs at 400 lx. Photovoltaic cells with ZnO/DNA composite ETLs based on PTB7:PC70BM blends, that absorb a broader range of the indoor lighting spectrum, delivered MPDs of 16.2 μW cm−2 with an estimated average PCE of 14.3% (best cell efficiency of 15.8%) at 400 lx. The best efficiencies for cells fabricated on flexible plastic substrates were 11.9% at 400 lx. This is the first report in which polymer photovoltaics incorporating biological materials have shown to increment performance at these low light levels and work very efficiently under indoor artificial light illumination. The finding can be useful for the production of more bio-compatible photovoltaics as well as bio-sensing devices based on organic semiconductors.

Self‐Assembly Metal Chelate as Ultraviolet Filterable Interface Layer for Efficient Organic Solar Cells

AbstractInterface engineering plays a vital role in the further improvement of efficiency and stability for organic solar cells (OSCs). Herein, a self‐assembly metal chelate based on hafnium and a designed ligand, N‐(4‐(3‐oxobutanoyl)phenyl)acetamide (ACBN) is applied as both interfacial modification layer and UV‐light filter in OSCs. The strong hydrogen‐bond induced intermolecular interaction enables Hf(ACBN)4 with the prerequisite of adequate solvent resistance to work as an electron transport layer (ETL) in the inverted OSCs. The self‐assembly behavior of Hf(ACBN)4 on the SnO2 film surface via constructing compact coordination structure has been verified via systematic theory calculations. In addition to optimizing the energy level alignment, the Hf(ACBN)4 modification effectively passivates the surface defect of SnO2 films for less surface charge recombination and a more efficient charge collection process. Thus, the OSCs with Hf(ACBN)4 layer yield a maximum PCE of 18.1%, better than that based on the bare SnO2 layer. Moreover, beneficial from the reduced oxygen vacancies via coordination effect and the UV‐light filter function of Hf(ACBN)4, the OSCs based on SnO2/ Hf(ACBN)4 composite ETL exhibit preferable stabilities under UV‐light irradiation or continuous operational conditions.

Suppressing charge recombination in planar perovskite solar cells by using SnO2/TiO2 nanocomposite as electron transfer layer

Hybrid perovskite solar cells (PSCs) have been paid great attention owing to their excellent photovoltaic properties. However, the presence of charge recombination at the interface of the electron transport layer (ETL)/perovskite hinders the performance of perovskite solar cells, preventing them from reaching the Shockley–Queisser limit. Herein, the SnO2/TiO2 nanoparticles (NPs) composite (S/T-NC) ETL is developed by adopting a simple method at low temperature and applied into planar PSCs. Our results show that the maximum power conversion efficiency of PSCs based on the S/T-NC ETL is 20.51% with a VOC of 1.09 V, a JSC of 24.15 mA/cm2, and a fill factor of 77.84%, much higher than that for both SnO2 NPs based PSCs (18.19%) and TiO2 NPs based PSCs (17.81%). Further analysis reveals that the mixing of TiO2 and SnO2 can improve film quality and reduce trap density, thus, suppressing charge recombination and improving stability. These findings prove that the use of SnO2/TiO2 composite ETL is an effective way to further improve the performance for planar PSCs.

Facile Surface Engineering of Composite Electron Transport Layer for Highly Efficient Perovskite Solar Cells with a Fill Factor Exceeding 81%

AbstractAfter perovskite became a star material, research on perovskite solar cells (PSCs) became a hot topic and developed rapidly. Electron transport layers (ETLs) with high mobility, low‐defect state, and suitable energy level arrangement dominate the development of planar heterojunction PSCs. In this work, the K+ and Cs+ doped composite SnO2 ETL (x mg KC‐SnO2) by a continuous spin‐coating of the x mg Cs+@KOH and SnO2 aqueous solution shows a substantial improvement in carries extraction, transport and collection properties, leading to the increased fill factor (FF) from 72.48% to 81.00% of the planar heterojunction PSCs, and finally the champion device average efficiency is 21.62%. Moreover, this work improves the interface contacts between ETL/Perovskite, as it reduces energy disorder and simultaneously promotes electron transport, charge extraction at the interface, improve energy level alignment and quasi‐Fermi level splitting, and decreased resistance for charge transfer in the device. In conclusion, this simple and effective method of improving the FF value provides a certain shortcut to the performance of plane heterogeneous perovskite devices.

Application of EDTA/SnO<sub>2</sub> double-layer composite electron transport layer to perovskite solar cells

Organic-inorganic hybrid perovskite solar cell devices have received wide attention because of their high efficiency, and interface problem is one of the key problems in the preparation of perovskite solar cells. An efficient double-layered ethylene diamine tetraacetic acid (EDTA)/SnO<sub>2</sub> composite structure, the ultrathin EDTA layer in contact with ITO electrode and an SnO<sub>2</sub> layer interfaced with the perovskite, is developed as an electron-transport layer (ETL) in the preparation of perovskite solar cells. It is interesting that the surface morphology of the top SnO<sub>2</sub> side of the composite ETL can be finely adjusted by tuning the underneath EDTA layer. These control the nucleation process in crystallization of the perovskite layer and adjust carrier extraction process between the electron transport and perovskite layers. High performance perovskite solar cells having a certified power conversion efficiency of 20.2% with negligible hysteresis are achieved.

ZnO:Bio-inspired polydopamine functionalized Ti3C2Tx composite electron transport layers for highly efficient polymer solar cells

The optimized electron transport layer (ETL) plays a crucial role in the practical application of polymer solar cells (PSCs). Herein, bio-inspired polydopamine (PDA) modified Ti3C2Tx (PDA-Ti3C2Tx) as a multifunctional additive is dispersed into ZnO to fabricate ZnO:PDA-Ti3C2Tx composite ETL. PDA-Ti3C2Tx passivates the trap states of ZnO via forming strong and stable chelate interactions through Zn2+ ions and PDA molecules. PDA-Ti3C2Tx also lowers the vacuum level of transport layer by forming interface dipoles between catechol of PDA and Zn2+ ions of zinc oxide. Moreover, PDA-Ti3C2Tx constructs additional electron transport pathways by connecting the discontinuities among ZnO nanocrystals. As such, ZnO:PDA-Ti3C2Tx composite ETL, with higher conductivity and proper work function, can effectively collect electrons in the PSCs. Compared with ZnO control devices, the performance of PSCs with ZnO:PDA-Ti3C2Tx ETL is obviously enhanced with power conversion efficiencies (PCEs) from 10.34% to 12.07% based on PBDB-T:ITIC, 14.84–16.69% based on PM6:Y6, and 8.14–9.41% for PTB7:PC71BM, respectively. The ambient stability of the PSCs with ZnO:PDA-Ti3C2Tx ETLs is significantly improved due to the increased hydrophobicity of ETL and the enhanced crystallinity of active layer. The novel ETLs provide a facile, eco-friendly, low-cost approach to realize the highly performance and stable PSCs.

Amino-capped zinc oxide modified tin oxide electron transport layer for efficient perovskite solar cells

Electron transport layer (ETL)/perovskite interface passivation is particularly challenging because of the use of polar solvents (e.g., DMF) for perovskite solution deposition, which usually destroy the bottom as-formed defect passivation layers. Herein, a novel multifunctional composite ETL, NH2[email protected]2, is prepared by mixing amino-capped ZnO (NH2-ZnO) nanocrystals (NCs) with SnO2 nanoparticles. The best-performing PSCs on the basis of NH2[email protected]2 achieve efficiency of 22.52%, which is significantly higher than that of the pristine SnO2 counterpart (18.45%). The enhanced performance of the NH2[email protected]2 ETL can be attributed to higher electron extraction capacity, better energy-level alignment with perovskite material, and more efficient carrier transport in device. Most important, the NH2 groups on the surface of ZnO NCs can effectively passivate the under-coordinated Pb2+ ions from perovskite films, thus reducing charge recombination at ETL/perovskite interface. The results suggest that NH2-ZnO [email protected]2 composite is a promising ETL for improving the performance of PSCs.

Designing a solution-processable electron transport layer for transparent organic light-emitting diode

In this work, the extensively used opaque metal cathodes of the conventionally structured OLEDs were replaced with the widely used transparent electrode indium tin oxide (ITO) for solution-processed transparent organic light-emitting diode (T-OLED). A new solution-processable electron transport layer (ETL), aside from facilitating the efficient injection of electrons into the T-OLED, protected the organic emission layer (EML) of the T-OLED against the plasma damage during top ITO cathode sputter deposition. The newly designed solution-processed ETL was the composite of the zinc oxide nanoparticles (ZnO-NPs), and cesium carbonate-doped ethoxylated polyethyleneimine (d-PEIE) with the semi-hydrophilic poly (methyl methacrylate) (PMMA) interlayer coated on the EML insured the good wettability and contact of the hydrophilic ETL with the hydrophobic EML. The solution-processed T-OLED emitted the total maximum luminance of about 2417 cd/m 2 (bottom side emission at 1455 cd/m 2 and top emission at 962 cd/m 2 ), total maximum current efficiency at 3.12 cd/A (bottom and top emissions at about 1.78 and 1.34 cd/A, respectively), and total maximum power efficiency at 1.64 l m/W (bottom and top emissions at about 0.95 and 0.69 l m/W, respectively) while having a very high optical transmittance of around 85% at 550 nm light wavelength. • The solution-processed T-OLED with newly designed composite ETL was fabricated. • The electrion injection efficiency and plasma barrier effect of the composite ETL was studied. • The composite ETL had the uniform morphology with even distribution of ZnO in the PEIE matrix. • The T-OLED with composite ETL showed excellent blue light emission.

Composite electron transport layer for efficient N-I-P type monolithic perovskite/silicon tandem solar cells with high open-circuit voltage

Perovskite/silicon tandem solar cells (PSTSCs) have exhibited huge technological potential for breaking the Shockley-Queisser limit of single-junction solar cells. The efficiency of P-I-N type PSTSCs has surpassed the single-junction limit, while the performance of N-I-P type PSTSCs is far below the theoretical value. Here, we developed a composite electron transport layer for N-I-P type monolithic PSTSCs with enhanced open-circuit voltage (VOC) and power conversion efficiency (PCE). Lithium chloride (LiCl) was added into the tin oxide (SnO2) precursor solution, which simultaneously passivated the defects and increased the electron injection driving force at the electron transfer layer (ETL)/perovskite interface. Eventually, we achieved monolithic PSTSCs with an efficiency of 25.42% and VOC of 1.92 V, which is the highest PCE and VOC in N-I-P type perovskite/Si tandem devices. This work on interface engineering for improving the PCE of monolithic PSTSCs may bring a new hot point about perovskite-based tandem devices.

NaCl-passivated and Na+-doped tin oxide electron transport layers enable highly efficient planar perovskite solar cells

Tin oxide (SnO2)-based electron transport layers (ETLs) are used to make flexible perovskite solar cells (PSCs) because of their low-temperature properties. However, when pure SnO2 is used, the poor interface formed between the SnO2 ETL and the perovskite layer is detrimental to the efficiency of the PSCs. In this work, we report the synthesis and characterisation of a SnO2–NaCl composite ETL. Na+ and Cl− at the ETL/perovskite interface passivate the ETL/perovskite contact and suppress nonradiative recombination centres. Meanwhile, Na+ diffuses from the ETL to the perovskite film, passivating its grain boundaries. The outstanding capability of Na + to increase the grain size and consequently improve the charge dynamics and increase the power conversion efficiency was also verified. PSCs with a SnO2–NaCl ETL exhibited an open-circuit voltage of 1.11 V, which was higher than the reference (1.08 V) for lower band gap perovskite absorbers, and achieved a power conversion efficiency of 18.56% with negligible hysteresis.

Diluted-CdS Quantum Dot-Assisted SnO2 Electron Transport Layer with Excellent Conductivity and Suitable Band Alignment for High-Performance Planar Perovskite Solar Cells.

An electron transport layer (ETL) with excellent conductivity and suitable band alignment plays a key role in accelerating charge extraction and transfer for achieving highly efficient planar perovskite solar cells (PSCs). Herein, a novel diluted-cadmium sulfide quantum dot (CdS QD)-assisted SnO2 ETL has been developed with a low-temperature fabrication process. The slight addition of CdS QDs first enhances the crystallinity and flatness of SnO2 ETLs so that it provides a promising workstation to obtain high-quality perovskite absorption layers. It also amazingly increases the conductivity of the SnO2 ETL by an order of magnitude and regulates the energy level matching between the SnO2 ETL and perovskite. These outstanding properties greatly accelerate the charge extraction and transfer. Thus, the MAPbI3-based PSCs with such a diluted-CdSQD-assisted SnO2 ETL achieve a maximum power conversion efficiency of 20.78% and obtain a better stability of devices in air. These findings testify the importance and potential of semiconductor QD modification on ETLs, which may pave the way for developing such composite ETLs for further enhancing photovoltaic performance of planar PSCs.