Efficient Electron Transport Layer Research Articles

Sol-gel derived mesoporous TiO2: Effects of non-ionic co-polymers on the pore size, morphology, specific surface area and optical properties analysis

Titanium dioxide (TiO2) nanoparticles were synthesized using sol-gel method and incorporated with co-polymers polyethylene glycol (PEG), polyvinylpyrrolidone (PVP) and pluronic F127 as pore forming agents. The samples were then calcined at 550 °C for 4 h to evaluate the effect of these co-polymers on the pore size and specific surface area. X-ray diffraction (XRD) analysis revealed a rutile phase with crystalline diffraction peaks. Crystal system of the observed rutile phase for all samples was tetragonal assigned to the group space P42/mm (136). Porous morphology was observed from scanning electron microscopy (SEM) images with spherical nanoparticles from all synthesized samples. Upon calcining at 550 °C, samples showed morphology with more and clear pores compared to as-prepared samples and mesoporous type was observed through Nitrogen adsorption – desorption isotherm measurements. Brunnauer–Emmet–Teller (BET) revealed the specific surface area of ∼69.82, 37.80 and 57.08 m2/g for TiO2@F127, TiO2@PVP and TiO2@PEG, respectively, after calcining at 550 °C. The pore size was found to be ∼13.01, 10.10 and 8.53 nm for TiO2@F127, TiO2@PVP and TiO2@PEG, respectively. Ultimately, the comparison of the non-ionic co-polymers on TiO2 is done to evaluate the morphological properties, specific surface area, porosity and optical properties that could promote TiO2 to act as an efficient electron transport layer in solar cells application.

Tin Oxide Electron Transport Layers for Air-/Solution-Processed Conventional Organic Solar Cells

Commercialization of organic solar cells (OSC) is imminent. Interlayers between the photoactive film and the electrodes are critical for high device efficiency and stability. Here, the applicability of SnO2 nanoparticles (SnO2 NPs) as the electron transport layer (ETL) in conventional OSCs is evaluated. A commercial SnO2 NPs solution in butanol is mixed with ethanol (EtOH) as a processing co-solvent to improve film formation for spin and slot-die coating deposition procedures. When processed with 200% v/v EtOH, the SnO2 NPs film presents uniform film quality and low photoactive layer degradation. The optimized SnO2 NPs ink is coated, in air, on top of two polymer:fullerene-based systems and a nonfullerene system, to form an efficient ETL film. In every case, addition of SnO2 NPs film significantly enhances photovoltaic performance, from 3.4 and 3.7% without the ETL to 6.0 and 5.7% when coated on top of PBDB-T:PC61BM and PPDT2FBT:PC61BM, respectively, and from 3.7 to 7.1% when applied on top of the PTQ10:IDIC system. Flexible, all slot-die-coated devices, in air, are also fabricated and tested, demonstrating the versatility of the SnO2 NPs ink for efficient ETL formation on top of organic photoactive layers, processed under ambient condition, ideal for practical large-scale production of OSCs.

Revival of Insulating Polyethylenimine by Creatively Carbonizing with Perylene into Highly Crystallized Carbon Dots as the Cathode Interlayer for High-Performance Organic Solar Cells.

The development of new electron transporting layer (ETL) materials to improve the charge carrier extraction and collection ability between cathode and the active layer has been demonstrated to be an effective approach to enhance the photovoltaic performance of organic solar cells (OSCs). Herein, water-soluble carbon dots (CDs) as ETL material have been creatively synthesized by a vigorous chemical reaction between polyethylenimine (PEI) and 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) via a simple one-step hydrothermal method. Taking full advantage of the high electron transfer property of PTCDA and the work function (WF) reduction ability of PEI, CD gained high electron mobility due to its large π-conjugated area and reduced the WF of indium tin oxide (ITO) by 0.75 eV. As for the photovoltaic performance of devices, inverted OSCs based on CDs have achieved a high power conversion efficiency (PCE) of 17.35%, exhibiting no burn-in effect with no reduction in PCE after more than 4000 h of storage. The successful application of CDs in OPV has developed a new avenue for designing efficient ETL materials that benefits the photovoltaic performance of OSCs.

Optimization of TiO2 paste concentration employed as electron transport layers in fully ambient air processed perovskite solar cells with a low-cost architecture

The optimization of thickness and surface roughness of the TiO 2 layer as an efficient electron transporting layer (ETL) plays a significant role on the performance improvement of perovskite solar cells (PSCs). In the present investigation, TiO 2 pastes synthesized with various concentrations under hydrothermal conditions were utilized to deposit the TiO 2 films of tunable porosities as the ETLs of PSCs. Also, the PSCs were fabricated with a structure of FTO/block-TiO 2 (b-TiO 2 )/m-TiO 2 /CH 3 NH 3 PbI 3 (MAPbI 3 )/CuInS 2 (CIS)/carbon as a low-cost architecture. Moreover, the effect of the TiO 2 paste concentration was studied on the performances of PSCs under fully ambient conditions. The optimal TiO 2 layer was constructed with 20 wt% TiO 2 paste concentration, which resulted in the formation of a hole‐free, smooth, and compact ETL layer. The champion perovskite solar cell fabricated with the 20 wt% TiO 2 paste concentration showed the highest power conversion efficiency (PCE) of 13.09% (J SC = 20.80 mA cm −2 , V OC = 0.98 V and FF = 0.64) but the champion PSC device made with the 10 wt% TiO 2 paste exhibited the lowest PCE = 8.05% (J SC = 19.83 mA cm −2 , V OC = 0.91 V and FF = 0.45). These results illustrated that the optimal 20 wt% TiO 2 paste caused ∼163% enhancement in the PCE of the device. Consequently, it could be suggested for application in fabrication of cost-effective and large scale PSCs. • Perovskite solar cells (PSCs) were fabricated by TiO 2 pastes of diverse concentrations. • Surface roughness and thickness of the TiO 2 electron transporting layers were optimized. • The optimal concentration of the mesoporous TiO 2 film was 20 wt%. • The highest efficiency (13.09%) was measured for the cell containing 20 wt% TiO 2 . • The champion device displayed FF = 0.64, J SC = 20.80 mA cm −2 and V OC = 0.98 V.

Graphene oxide decorated with gold enables efficient biophotovolatic cells incorporating photosystem I.

This paper describes the use of reduced graphene oxide decorated with gold nanoparticles as an efficient electron transfer layer for solid-state biophotovoltic cells containing photosystem I as the sole photo-active component. Together with polytyrosine–polyaniline as a hole transfer layer, this device architecture results in an open-circuit voltage of 0.3 V, a fill factor of 38% and a short-circuit current density of 5.6 mA cm−2 demonstrating good coupling between photosystem I and the electrodes. The best-performing device reached an external power conversion efficiency of 0.64%, the highest for any solid-state photosystem I-based photovoltaic device that has been reported to date. Our results demonstrate that the functionality of photosystem I in the non-natural environment of solid-state biophotovoltaic cells can be improved through the modification of electrodes with efficient charge-transfer layers. The combination of reduced graphene oxide with gold nanoparticles caused tailoring of the electronic structure and alignment of the energy levels while also increasing electrical conductivity. The decoration of graphene electrodes with gold nanoparticles is a generalizable approach for enhancing charge-transfer across interfaces, particularly when adjusting the levels of the active layer is not feasible, as is the case for photosystem I and other biological molecules.

Modeling and optimization of CZTS kesterite solar cells using TiO2 as efficient electron transport layer

In this paper, a numerical simulation study via AMPS 1D simulator is carried out to investigate the degradation mechanisms occurred in hybrid Cu2(Zn,Sn)Se4 (CZTS) solar cells that use a nonporous n-type-TiO2 material as a window. The advantageous Spike-like conformation against recombination at the TiO2/CZTS interface, which is ensured by the band-engineering offset established using TiO2 material, is discussed. The influence of the geometrical and physical parameters on the device fundamental figures of merit is assessed. Besides, the degradation effect linked to both deep and tail states situated in the gap of the materials, and the effective working temperature, are taken into account. The results reveal that the actual defect type (donor or neutral) at the Cu2ZnSnS4 layer has a harsh influence on the device performance. This is attributed to the raised Shockley–Read–Hall (SRH) recombination highlighted by investigating the variation of the carrier density along the absorber layer. A low barrier height at the back contact (ϕbl = 0.1 eV) and a suitable doping level and thickness of both the window (ND = 4 × 1017 cm−3, WTiO2 = 0.02 µm) and the absorber (NA = 6.5 × 1016 cm−3, WCZTS = 3.2 µm) layers could efficiently improve the device performance.

Low‐Temperature Atomic Layer Deposited Electron Transport Layers for Co‐Evaporated Perovskite Solar Cells

In this work, we explore the potentials and the characteristics of electron‐transporting layers (ETL) grown by atomic layer deposition (ALD) at low temperature in co‐evaporated perovskite solar cells (PSCs). The thermal‐based ALD process has been investigated by tuning the main growing conditions as the number of cycles and the growth temperature. We show that un‐annealed ALD‐SnO2 thin films grown at temperatures between 80 °C and 100 °C are efficient ETL in n.i.p co‐evaporated MAPbI3 PSCs which can achieve power conversion efficiencies (PCEs) consistently above 18%. Moreover, the champion PSC achieved a PCE of 19.30% at 120 °C with 150 cycles. We show that the low‐temperature processed ALD SnO2 is very promising for flexible, large‐area PSCs and mini‐modules. We also report the first co‐evaporated PSCs employing low temperature processed ALD ZnO with PCEs approaching 18%. This work demonstrates the potential of the low‐temperature ALD deposition method as a potential route to fabricate efficient PSCs at low temperatures.

Highly efficient and durable electron transport layer for QDSSC: An integrated approach to address recombination losses

Quantum dot sensitized solar cells (QDSSC) are up-and-coming low cost third-generation solar cells technology. The distinctive properties of quantum dots (QDs) feature QDSSC as an optimistic future of photovoltaics. The real concern with these devices is the wide band gap semiconductors used as the electron transport layer. Electron transport layers in quantum dot sensitized solar cells suffer from performance losses arising from recombination of electrons. This work tries to entail an integrated approach of tailoring the nanostructure as an exclusive electron transport layer to overcome the recombination losses. We adopted doping of Neodymium into TiO2 (Nd-TiO2) to create intermittent band gap states that can extend the charge carrier lifetime and rendered the defect material (Nd-TiO2) as a hybrid composite with 1D Graphene nanoribbons for quick electron extraction. This approach carefully alters ETL's functionality, and its utility has emerged into a potential electrode for QDSSC. Our tailored photoanode reports a higher efficiency of ~ 6% for cadmium sulfide QDs deposited via successive ionic layer adsorption and reaction (SILAR) and stands as highly efficient photoanode for QDSSC. This opens a clear channel in the realm of applications like photocatalysis, photovoltaics, and energy devices that involve metal oxide nanostructures for efficient charge separation.

Low-temperature fabrication of perovskite solar cells using modified TiO2 electron transport layer

Low-temperature preparation of efficient electron transport layer (ETL) can effectively expand the application of perovskite solar cells (PSCs). We herein introduce anatase TiO2 nanoparticles (NPs) with an average diameter of 15 nm prepared by hydrothermal method and optimized with acetic acid (AA) as well as oleic acid (OA). The Ti3+ as well as Ti–OH signals indicate the surface defects of TiO2 NPs investigated by X-ray photoelectron spectroscopic (XPS) are observed to be passivated by the modifiers through chelate or bridging pattern. Thus, when the modified NPs are dispersed into the precursor for spin-coating ETLs under 150 °C, higher power conversion efficiency (PCE) of 20.15% and 19.41% is achieved based on planar structured PSC using TiO2 modified with AA and OA, respectively. The device stability is also considerably increased. Analyzed by photoluminescence and electrochemical impedance spectroscopies, the improved cell performance can be ascribed to the reduced charge transport resistance, enhanced electron extraction, and suppressed recombination behavior. We anticipate this facile approach of fabricating efficient TiO2 ETLs can be further employed into PSCs commercialization.

N-Type Self-Doped Hyperbranched Conjugated Polyelectrolyte as Electron Transport Layer for Efficient Nonfullerene Organic Solar Cells.

The electron transport layer (ETL) exerts a dramatic influence on the power conversion efficiency (PCE) of the nonfullerene organic solar cells (NOSCs). Currently, the majority of the organic ETLs possess a relatively poor conductivity, which is not conducive to carrier transport and collection. Herein, we design and develop a novel hyperbranched conjugated polyelectrolyte (CPE) based on n-type perylene diimide (PDI) as the center core and quaternary ammonium salt as the side polar groups. The lone pair electrons of the nitrogen atoms can transfer to the electron deficient PDI core and endow the molecule with an efficient n-type self-doping effect. Moreover, the hyperbranched structure makes the molecule functionalized with more side polar groups, favoring forming more dipoles and stronger dipole moments. Therefore, the CPE PTPAPDINO possesses a high conductivity and can notably decrease the work function (WF) of the electrode, contributing to the carrier transport and collection of the device. The NOSC with PTPAPDINO as ETL delivers an excellent PCE of 15.62%, which is even superior to the device using the classical PDINO ETL. Moreover, the PCE can retain 82.6% of the optimal device when the thickness has been increased to 28 nm. These results manifest that it is a feasible strategy to design an n-type self-doping hyperbranched CPE as efficient ETL, and PTPAPDINO is a promising alternative ETL for high performance NOSCs.

Perovskite Metal–Oxide–Semiconductor Structures for Interface Characterization

AbstractPerovskite solar cells (PSCs) are one of the most promising photovoltaic technologies. Amongst several challenges, developing and optimizing efficient electron transport layers that can be up‐scaled still remains a massive task. Admittance measurements on metal–oxide–semiconductor (MOS) devices allow to better understand the optoelectronic properties of the interface between perovskite and the charge carrier transport layer. This work discloses a new pathway for a fundamental characterization of the oxide/semiconductor interface in PSCs. Inverted MOS structures, that is, glass/fluorine‐doped tin oxide/tin oxide (SnO2)/perovskite are fabricated and characterized allowing to perform a comparative study on the optoelectronic characteristics of the interface between the perovskite and sputtered SnO2. Admittance measurements allow to assess the interface fixed oxide charges (Qf) and interface traps density (Dit), which are extremely relevant parameters that define interface properties of extraction layers. It is concluded that a 30 nm thick SnO2 layer without annealing presents an additional recombination mechanism compared to the other studied layers, and a 20 nm thick SnO2 layer without annealing presents the highest positive Qf values. Thus, an effective method is shown for the characterization of the charge carrier transport layer/perovskite interface using the analysis performed on perovskite‐based inverted MOS devices.

The low temperature pyrolysis preparation of In2S3 thin film and its application in Sb2S3 thin film solar cells

In2S3 thin films were successfully prepared by the low temperature pyrolysis of indium-butyldithiocarbamate (In-BDCA) complex at 200 °C for 30 min and first applied as the electron transport layer in Sb2S3 thin film solar cells. The influence of the In-BDCA complex content in the precursor solution on the microstructure of the In2S3 thin films was investigated and the photovoltaic performance of the corresponding Sb2S3 thin film solar cells was evaluated. The result revealed that In2S3 thin film with 2:1 possessed compact and full-coverage surface morphology and its thickness was 25 nm. The corresponding Sb2S3 thin film solar cells achieved the photoelectric conversion efficiency (PCE) of 2.87% with the open-circuit voltage (Voc) of 0.60 V, short-circuit current density (Jsc) of 10.38 mA cm−2, fill factor (FF) of 46.40%. When the preparation temperature of Sb2S3 thin films increased from 200 °C to 300 °C, the corresponding Sb2S3 thin film solar cells achieved the PCE of 4.03% with the Voc of 0.66 V, Jsc of 12.56 mA cm−2, FF of 48.63%. This result demonstrated that the In2S3 thin film can be applied as the efficient electron transport layer in Sb2S3 thin film solar cells.

Universal electron transporting layers via mixing two homostructure molecules with different polarities for organic light-emitting diodes

In general, electron transport layer (ETL) in organic light-emtting diodes (OLEDs) consists of single component of electron transporting material (ETM) or a mixture with n-dopant such as 8-hydroxyquinolinolato-lithium (Liq). However, there exists a limit to controlling a wide range of carrier density in OLEDs according to the required characteristics of the devices due to electrically insulating property of Liq. Here, we suggest a universal strategy to construct an efficient ETL. We synthesized two ETMs, diphenyl-[4-(10-phenyl-anthracene-9-yl)-phenyl]-amine (An-Ph) and phneyl-[4-(10-phenyl-anthracene-9-yl)-phenyl]-pyridin-3-yl-amine (An-Py) that have the same core structures with different polarities in functional groups. The electrical characteristics of electron-only-devices (EODs) were investigated by space charge limited current (SCLC) modeling and impedance spectroscopy analysis. Interestingly, the homostructure type ETL composed of An-Ph and An-Py showed not only superior electron transporting capability, but also the possibility of controlling electron injection and transporting in a wide range compared to the heterostructure type ETL of An-Ph and Liq. Compared to the An-Ph-only EOD, the electron mobility in 75% An-Py-mixed homostructure EOD increased by almost 4 orders of magnitude. Such dramatic variation of electron mobility was achieved thanks to the molecular design strategy to separate charge injection and charge transport regions within a molecule, which consequently induced the giant surface potential (GSP) effect between the ETL/cathode interface. As a result, the external quantum efficiency (EQE) of blue fluorescent and phosphorescent OLEDs with the homostructure ETLs was enhanced by 28.6% and 34%, respectively, compared to that of each control device without manipulating outcoupling effects. • The anthracene-based electron transporting materials, An-Py and An-Ph with different polarities were designed and synthesized for universal electron transporting layers. • The superior charge injection property was comprehensively investigated with impedance spectroscopy and attributed to the giant surface potential in the ETL. • Compared to Liq-based ETL, the EQE of fluorescent and phosphorescent OLEDs with An-Py and An-Ph ETL was enhanced by 28.6% and 34%, respectively.

Non-conjugated natural alginate as electron-transport layer for high performance polymer solar cells after modification

The search for the alternatives to expensive synthesized conjugated polymers as interfaces in polymer solar cells (PSCs), which could largely decrease the cost and promote the commercialization process of PSCs, is now highly relevant. To introduce natural polymer as the interface layer for the high-efficiency PSCs would be a potential choice. In this study, a purely natural polysaccharide from ocean without any conjugated structure, sodium alginate (SA), is utilized as efficient electron transport layer (ETL) to replace the conjugated star molecule, poly [(9,9-bis(3'-(N,NdiMethyl)-NethylaMMoiniuM-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)]dibroMide (PFN–Br), and modify the aluminum (Al) electrode in conventional PSCs. The reduction of the work function of Al is successfully achieved by SA forming a dipole and keeping the ohmic contact at the interface. Meantime, the ideal charge transfer and exciton dissociation are realized, along with decreasing charge recombination, resulting in a comparable power conversion efficiency (PCE) with devices of PFN-Br as ETL. For poly([2,6′-4,8-di(5-ethylhexylthienyl)benzo[1,2-b; 3,3-b]dithiophene]3-fluoro-2[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl):[6,6]-phenyl-C71-butyric acid methyl ester (PTB7-Th:PC71BM) system, PCE is increased to 9.5% and for Poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo[1,2-b:4,5-b’]dithio-phene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c’]dithio-phene-4,8-dione)]:3,9-bis(2methylene-((3-(1,1-dicyanomethylene)-6,7-difluoro)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d']-s-indaceno[1,2-b:5,6-b'] dithiophene (PM6:IT-4F) system, PCE 13.4%, respectively, which illustrates a promising future for photovoltaic research of natural alginate non-conjugated polyelectrolyte in conventional PSCs.

Electron Transport Layers Based on Oligo(ethylene glycol)-Incorporated Polymers Enabling Reproducible Fabrication of High-Performance Organic Solar Cells

Interlayers in organic solar cells (OSCs) play a crucial role in determining their charge extraction properties, device performance, and stability. In this work, two naphthalene diimide (NDI)-based n-type polymers (P(NDIDEG-T) and P(NDITEG-T)) incorporating oligo(ethylene glycol) (OEG) side chains of different lengths are designed and used as new electron transport layers (ETLs) in OSCs. The hydrophilic OEG side chains enable the processing of these n-type polymers using eco-friendly water/ethanol mixtures. In addition, the polar OEG groups effectively modify the work function of the Ag cathode, enabling the polymers to function as efficient ETLs. Consequently, when these OEG-based ETLs are applied to PM6:Y6-based OSCs, a maximum power conversion efficiency (PCE) of 15.43% is achieved, which is substantially higher than that of a reference OSC without an ETL (9.93%) and comparable to that of an OSC with a representative high-performance PFN-Br ETL (15.34%). We demonstrate that the P(NDIDEG-T)-based OSCs show both enhanced PCEs and better reproducibility than their P(NDITEG-T)-based counterparts, which are attributed to the lower surface tension and improved film uniformity of the P(NDIDEG-T) ETL. Also, the P(NDIDEG-T) ETL realizes OSCs with higher storage stability and more thickness-tolerant performance compared to the P(NDITEG-T) and PFN-Br ETLs. Our study provides useful guidelines for the design of ETLs suitable for the fabrication of high-performance, reproducible, and stable OSCs.

N-doped anatase TiO2 as an efficient electron transport layer for mesoporous perovskite solar cells

In this work, anatase N-doped TiO2 was prepared by a facile pre-sintering method. The usage of N-doped TiO2 not only improved the electrical performance of the electron transport layer, but prevented high-temperature sintering of the substrate. As a result, the devices with N-doped TiO2 exhibited higher average power conversion efficiency of 16.65%. Furthermore, N-doped TiO2 was used in flexible devices, and high performance of flexible perovskite solar cells with power conversion efficiency of 14.52% was achieved. Consequently, the preparation of N-doped TiO2 could be a promising method for boosting the development of flexible perovskite solar cells.

Magnesium doped TiO2 as an efficient electron transport layer in perovskite solar cells

Perovskite solar cells (PSCs) are rapidly emerging as efficient solar cells due to the efficient photovoltaic and physiochemical properties. Ideally, the absorber layer in PSCs is sandwiched between highly conductive electron transport layer (ETL) and highly stable hole transport layer (HTL). The interfaces between these layers highly affect the performance of PSCs. In this study Magnesium (Mg) doped TiO2 based ETL is systematically investigated to enhance the optical and morphological properties of the layer and the interface. It was observed that with Mg doping in mesoporous TiO2, morphology of TiO2 based ETL film was significantly improved thereby providing an interface for the growth of absorber layer. Optoelectronic studies suggested that band gap was effectively reduced with the addition of Mg and absorption range was also enhanced. Electrical analysis yielded, Mg doped TiO2 based ETL showed enhanced conduction and better sheet carrier mobility as compared to undoped films. Thermal studies indicate fabrication of a thermally stable ETL material for PSCs. Moreover, Current density-Voltage (J-V) measurements indicated more than two-fold increase in photovoltaic efficiency of 3 wt% Mg.

Reduced extrinsic recombination process in anatase and rutile TiO2 epitaxial thin films for efficient electron transport layers

TiO2 is the most widely used material for the electron transport layers (ETLs) because it is characterized by proper band alignment with light absorbers, adequate optical transmittance, and high electron mobility. There are two thermodynamically stable crystal phases of TiO2: anatase and rutile. However, understanding which phase is more effective as the ETL is still required. In this paper, we demonstrate the different effects of using epitaxial anatase TiO2 and epitaxial rutile TiO2 (both grown using pulsed laser deposition) as the ETL material on the electrical and optical properties. Epitaxial Nb-doped TiO2 layers were used as the common electrode material for the both epitaxial ETLs for which the crystalline structural analysis revealed high crystalline qualities and good coherency for both phases. By analyzing the recombination kinetics, the anatase phase shows a preferable performance in comparison with the rutile phase, although both epitaxial phases show remarkably reduced extrinsic recombination properties, such as trap-assisted recombination. This study demonstrates not only a better electron transporting performance of anatase phase but also reduced extrinsic recombination through epitaxy growth.

Double‐layered SnO2/NH4Cl‐SnO2 for efficient planar perovskite solar cells with improved operational stability

AbstractTin oxide (SnO2) is widely used as an electron transport layer (ETL) to fabricate planar perovskite solar cells (PSCs) due to their easy and low‐temperature processed fabrication. Enhancing carrier extraction and energy level alignment at the perovskite/SnO2 interface is vital to improve the device performance further. Here, we demonstrate a double‐layered SnO2/ NH4Cl‐SnO2 as an efficient ETL. The top NH4Cl‐SnO2 shows a better energy level alignment with the perovskite and reduced alkalinity to avoid perovskite degradation, resulting in enhanced electron extraction efficiency and interfacial stability. Furthermore, the bottom SnO2 retains the capability of efficient carrier transport to avoid charge accumulation. As a result, we achieve a champion device with a power conversion efficiency of 21.01% and negligible hysteresis. Moreover, the corresponding PSCs show much improved operational stability, retaining 80% of the initial efficiency after 1090 hours of operation at the maximum power point under 1‐sun illumination. While the pristine SnO2 based PSCs only insist on 278 hours before losing 20% of the initial efficiency.

Flexible Solar Cells: Low‐Temperature‐Deposited TiO2 Nanopillars for Efficient and Flexible Perovskite Solar Cells (Adv. Mater. Interfaces 3/2021)

Sunlight can be converted to electricity via solar cells, with which then light can be generated the other way around. In this regard, skyscrapers performing light show during night or the bright Karst landscape under the ground are exemplified, echoing the geometry of the TiO2 nanopillars which are fabricated via a low-temperature dry process and work as the efficient electron-transporting layer in flexible perovskite solar cells. More details can be found in article number 2001512 by Zhifeng Huang, Zijian Zheng, and co-workers.