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A pristine electron transport layer (ETL) usually delivers relatively low device performance due to high defect density and/or poor contact. Interface modification has been demonstrated to be one o...

The mesoscopic electron transport layer (m-ETL) has been demonstrated to help perovskite solar cells (PSCs) construct a tough interface against stress and a good contact for efficient extraction of...

In recent years, the perovskite solar cells have gained much attention because of their ever-increasing power conversion efficiency (PCE), simple solution fabrication process, flyable, light-weight wearable and deployable for ultra-lightweight space and low-cost materials constituents etc. Over the last few years, the efficiency of perovskite solar cells has surpassed 25% due to high-quality perovskite-film accomplished through low-temperature synthesis techniques along with developing suitable interface and electrode-materials. Besides, the stability of perovskite solar cells has attracted much well-deserved attention. In this article we have focused on recent progress of the perovskite solar cells regarding their crystallinity, morphology and synthesis techniques. Also, demonstrated different layers such as electron transport-layers (ETLs), hole transport-layers (HTLs) and buffer-layers utilized in perovskite solar-cells, considering their band gap, carrier mobility, transmittance etc. Outlook of various tin (Sn), carbon and polymer-based perovskite solar cells and their potential of commercialization feasibility has also been discussed.

Suitable electron transport materials bearing good interfacial contact, improved electron transport ability, and matched energy levels are indispensable for developing efficient perovskite solar cells (PSCs). Herein, regular (n‐i‐p) planar Cs0.05FA0.83MA0.12PbI2.55Br0.45 (CsFAMA) PSC devices were fabricated using a pyridine‐functionalized fullerene derivative (C60‐3‐BPy) as an independent electron transport layer (ETL), delivering a decent power conversion efficiency (PCE) of 18.22%, which is dramatically higher than that of the control device based on [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) ETL (15.70%). The energy level offset between C60‐3‐BPy and the perovskite is smaller than that based on PCBM ETL, which is beneficial for efficient ohmic contact in ETL/perovskite interface and improved open‐circuit voltage (Voc). Moreover, C60‐3‐BPy affords strong coordination interactions with perovskite, leading to an improved film quality of the perovskite layer with enlarged grain size and decreased trap state density, which contribute to facilitated electron extraction as reflected by the increases of both the fill factor (FF) and the short‐circuit current (Jsc). C60‐3‐BPy‐facilitated electron extraction further results in hysteresis‐free devices.

Achieving long‐term device stability is one of the most challenging issues that impede the commercialization of perovskite solar cells (PSCs). Recent studies have emphasized the significant role of the cathode interfacial layer (CIL) in determining the stability of inverted p‐i‐n PSCs. However, experimental investigations focusing on the influence of the CIL on PSC degradation have not been systematically carried out to date. In this study, a comparative analysis was performed on the PSC device stability by using four different CILs including practical oxides like ZnO and TiOx. A new implemented co‐doping approach was found to results in high device performance and enhanced device stability. The PSC with a thick film configuration of chemically modified TiOx CIL preserves over 77 % of its initial efficiencies of 17.24 % for 300 h under operational conditions without any encapsulation. The PSCs developed are among the most stable reported for methylammonium lead iodide (MAPbI3) perovskite compositions., In for the CIL: Highly stable inverted perovskite solar cells (PSCs) are assembled by using chemically modified titanium suboxide (TiOx) as the cathode interfacial layer (CIL). Codoping enhances the electrical properties of the TiOx CIL, providing better inner encapsulation with thick film configuration. The PSCs exhibit significantly improved operational stability, maintaining >77 % of their initial efficiencies for up to 300 h without encapsulation.

Carbon-based perovskite solar cells are competitive candidate for photovoltaic applications in future due to their high-performance, low-cost and good stability. However, the hole transport materials are limited and their properties are not satisfying in carbon-based perovskite solar cells. Here, we report a typical p-type P3HT as hole transport layer for all low-temperature processed carbon-based perovskite solar cells with ZnO electron transport layer. Because P3HT has energy level matching with perovskite film and can facilitate the hole collection process, the power conversion efficiency of device can reach 16.05% that far higher than devices without P3HT hole transport layer. More importantly, due to good hydrophobicity and encapsulation function of P3HT, the stability of devices can also be significantly improved. The power conversion efficiency of device is able to retain over 90% of their initial value over 1200 h upon ambient air exposure without encapsulation. This present study provides a simple strategy for fabricating low-cost, highly efficient and stable perovskite solar cells.

As an effective electron transport layer, tin oxide (SnO2) has attracted much attention owing to its charge mobility and chemical stability, but it still suffers from high trap at the SnO2/perovski...

The electron transport layer (ETL) plays an important role as a buffer layer in the efficient n-i-p planar heterojunction perovskite solar cells (PSCs). Recently, a new ETL, (CH3)2Sn(COOH)2 (CSCO),...

Despite demonstrating remarkable power conversion efficiencies (PCEs), perovskite solar cells (PSCs) have not yet achieved their full potential. In particular, the interfaces between the perovskite and charge transport layers account for the vast majority of the recombination losses. Interfacial contact and band alignment between the low-temperature-processed TiO2 electron transport layer (ETL) and the perovskite are essential to minimize nonradiative recombination losses. In this study, a CeOx interlayer is employed to modify the perovskite/TiO2 interface, and the charge transport properties of the devices are investigated. The bilayer-structured TiO2/CeOx ETL leads to the modification of the interface energetics, resulting in improved electron extraction and reduced nonradiative recombination in the PSCs. Devices based on TiO2/CeOx ETL exhibit a high open-circuit voltage (Voc) of 1.13 V and an enhanced PCE of more than 20% as compared with Voc of 1.08 V and a PCE of approximately 18% for TiO2-based devices. Moreover, PSCs based on TiO2/CeOx ETL maintain over 88% of their initial PCEs after light illumination for 300 min, whereas PSCs based on TiO2 ETL almost failed. This study provides an efficient strategy to enhance the PCE and stability of PSCs based on a low-temperature-processed TiO2 ETL.

Highlights The (SnO2-cPCN) ETL shows superior electron mobility of 3.3 × 10−3 cm2 V−1 s−1, which is about three times higher than that of pristine SnO2.The less wettable SnO2-cPCN leads to perovskite layers with reduced grain boundaries and enhanced qualities due to suppressed heterogeneous nucleation of perovskite.The PSCs based on SnO2-cPCN showed negligible J–V hysteresis and two champion PCE of 23.17% and 20.3% on devices with 0.1 and 1 cm2 active area, respectively. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-021-00636-0., Efficient electron transport layers (ETLs) not only play a crucial role in promoting carrier separation and electron extraction in perovskite solar cells (PSCs) but also significantly affect the process of nucleation and growth of the perovskite layer. Herein, crystalline polymeric carbon nitrides (cPCN) are introduced to regulate the electronic properties of SnO2 nanocrystals, resulting in cPCN-composited SnO2 (SnO2-cPCN) ETLs with enhanced charge transport and perovskite layers with decreased grain boundaries. Firstly, SnO2-cPCN ETLs show three times higher electron mobility than pristine SnO2 while offering better energy level alignment with the perovskite layer. The SnO2-cPCN ETLs with decreased wettability endow the perovskite films with higher crystallinity by retarding the crystallization rate. In the end, the power conversion efficiency (PCE) of planar PSCs can be boosted to 23.17% with negligible hysteresis and a steady-state efficiency output of 21.98%, which is one of the highest PCEs for PSCs with modified SnO2 ETLs. SnO2-cPCN based devices also showed higher stability than pristine SnO2, maintaining 88% of the initial PCE after 2000 h of storage in the ambient environment (with controlled RH of 30% ± 5%) without encapsulation. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-021-00636-0.

The past few years have witnessed the rapid development of all-inorganic perovskite solar cells (PSCs). The interface of the electron transport layer (ETL)/perovskite is the vital charge separation...

SnO2 has been the most commonly used electron transport layer (ETL) in perovskite solar cells (PSCs) due to its excellent electron mobility and stability. To meet the applications of SnO2 ETL in la...

Abstract As a promising photovoltaic technology, perovskite solar cells (pero-SCs) have developed rapidly over the past few years and the highest power conversion efficiency is beyond 25%. Nowadays, the planar structure is universally popular in pero-SCs due to the simple processing technology and low-temperature preparation. Electron transport layer (ETL) is verified to play a vital role in the device performance of planar pero-SCs. Particularly, the metal oxide (MO) ETL with low-cost, superb versatility, and excellent optoelectronic properties has been widely studied. This review mainly focuses on recent developments in the use of low-temperature-processed MO ETLs for planar pero-SCs. The optical and electronic properties of widely used MO materials of TiO2, ZnO, and SnO2, as well as the optimizations of these MO ETLs are briefly introduced. The commonly used methods for depositing MO ETLs are also discussed. Then, the applications of different MO ETLs on pero-SCs are reviewed. Finally, the challenge and future research of MO-based ETLs toward practical application of efficient planar pero-SCs are proposed. Graphical abstract

Interests in minimalist device structure design of perovskite solar cells (PSCs) have accelerated the rapid advances of electron transport layer-free PSCs by composition and solvent engineering. Fo...

The development of perovskite solar cells (PSCs) as an efficient and cost-effective alternative to traditional approaches to solar energy transduction has received much recent attention, and there has been considerable progress made with reported power conversion efficiencies now surpassing 25%. This development is encouraging and is a result of intensive research on device design, factors affecting long-term stability of PSCs, and systematic material development in which electron transport layer (ETL) materials play a crucial role to afford high-performance PSC devices. ETL materials, including (6-(1,10-phenanthrolin-3-yl)naphthalen-2-yl)diphenylphosphine oxide (Phen-NaDPO), and n-type materials based on the naphthalene diimide (NDI) structure, appear to be amongst the most promising materials to date. This article provides an up-to-date review on organic n-type ETL materials, both polymeric and small molecules, based on NDI format, detailing reports of structures with key relevant parameters, such as the efficiency and stability of PSCs. The review is written from a perspective of organic chemistry and we believe this will provide fundamental advice on the future design of new ETL materials based on NDIs that will afford more efficient and stable PSCs.

UV induced decomposition of perovskite material is one of the main factors to severely destroy perovskite solar cells for instability. Here we report a UV stable perovskite solar cell with an Fe2O3 electron transport layer (ETL) made by spin-coating water dispersed Fe3O4 nanoparticles. Devices with Fe2O3 ETLs prepared from 10 nm Fe3O4 nanoparticles show nearly no decrease of photoelectric conversion efficiency (PCE) upon continuous exposure to very high UV light irradiation (300 W Xe lamp) for 10 hours in contrast to the TiO2 ETL based samples with more than 30% reduction of PCE, and their PCE (14.33) is also much superior to those of devices with Fe2O3 ETLs made conventionally from FeCl3 solution (7.7%). Through the study of Fe2O3 thin film prepared perovskite solar cells, it is found that compact, high transmittance, low leakage and low transmission impedance devices can be obtained by using an appropriate size of Fe3O4 nanoparticles. Our major findings are expected to provide a guide to design UV-protected compact electron transport layers for UV-stable perovskite solar cells.

The experimental search for high-efficiency perovskite solar cells (PSCs) is an extremely challenging task due to the vast search space comprising the materials, device structures, and preparation methods. Herein, using a two-step machine learning approach and 2006 PSC experimental data points extracted from 880 articles published between 2013 to 2020, we develop some heuristics for high-efficiency PSC and power conversion efficiency (PCE) improvement induced by doping of the electron transport layer (ETL). We show that the utilizations of SnO2 and TiO2 ETLs, mixed-cation perovskites, dimethyl sulfoxide and dimethylformamide perovskite precursor solvents and anti-solvent treatment are the most significant factors that lead to the high PCEs of PSCs. The PCE can be further improved by ETL doping for tuning the conduction band minimum, Fermi level, and conductivity of the ETL. Moreover, we predict that a FA–MA based PSC with a Cs-doped TiO2 ETL and a Cs–FA–MA based PSC with S-doped SnO2 ETL exhibit PCEs of as high as 30.47% and 28.54%, respectively. This study provides insightful guidance for the development of high-efficiency PSCs.

The industrialization of perovskite solar cells (PSCs) is based on the development of efficiency and stability. Here, a composite film of a polyethylenimine ethoxylated (PEIE) and tellurophene-based two-dimensional metal–organic framework (2D MOF) was introduced to realize the nondestructive passivation of TiO2. This interfacial layer can not only realize the effective passivation of TiO2, but can also further improve the morphology of the perovskite film. After the modification of the PEIE-2D MOF composite film, the morphology and crystallinity of the perovskite film are greatly optimized, the trap states in the TiO2 layer are reduced, and the electron transport in the device is enhanced, thus finally achieving highly efficient and stable FA0.25MA0.75PbI3 PSCs with a maximum efficiency of 22.22%. It was demonstrated that the reduced trap states and the smooth surface of the TiO2 electron transport layer are the reasons for the high performance of modified PSCs. This method provides a new way for improving the interface state to achieve highly efficient and stable PSCs.

Improved device performance of perovskite light-emitting diodes (LEDs) is demonstrated through the synergistic effect of the optimized CsPbI3 nanocrystals (NCs) as the emissive layer (EML) and ZnO/...

The study focuses on optoelectronic model of perovskite solar cell using finite element method to optimize the thickness of electron transport and absorber layers implemented using COMSOL multi-physics modeling. The analyzed perovskite solar cell shows a power conversion efficiency of 17.95% for an optimum film thickness of TiO2 (90 nm)/CH3NH3PbI3 (100 nm)/Spiro-OMeTAD (300 nm). The obtained simulated results were examined to improve the efficiency of the device and also to understand the impact of factors affecting the performance of the solar cell. Furthermore, the working potential of perovskite solar cell was explored to demonstrate the impending scope of stepwise progress in the novel technology.

Vertically aligned ZnO nanorods were grown using the chemical deposition method. The presence of various ZnO seed layers in the growth process was examined. Perovskite cells, with these films, were...

Among deposition methods, ultrasonic spray-coating has particularly strong potential for large-scale production due to its low cost and capability to produce thin films with large-scale areas for i...

Recently, organic–inorganic hybrid metal halide perovskite (O-IHMHP) has been diffusely used in solar cells due to its remarkable photoelectric property and inexpensive film-forming process. Since organic–inorganic hybrid metal halide perovskite solar cells (O-IHMHPSCs) were introduced in 2009, their photoelectric conversion efficiency has been increased to 25.2%, and their lifespan has been extended to tens of thousands of hours. However, due to processing factors, defects consist in the interfaces of O-IHMHP with the electron transport layer and the hole transport layer. To improve the stability and property of O-IHMHPSCs, these defects must be addressed; to do so, passivation is commonly applied at the interface. This work reviews research on the interface passivation of O-IHMHPSCs. Here, the passivation mechanisms of different additives on the interface defects of O-IHMHP films are analyzed, their impacts on the stability and property of O-IHMHPSCs are compared, and their roles in O-IHMHPSCs are summarized. Finally, the research and development trends of the defect passivation of O-IHMHPSCs are discussed.

In the past few years, the power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have increased from 3.81 to 25.2%, surpassing those of all almost all thin films solar cells. For hi...

Tin oxide (SnO2) has recently emerged as a promising electron transport layer for perovskite solar cells (PSCs) in light of the material’s optical and electronic properties and its low-temperature ...

In recent years, perovskite material has been extensively studied due to its unique physical properties and promising application in the third generation of solar cells. In particular, Sn-based perovskite has been considered to replace Pb-based perovskite because of the toxic effects and it can lead to other serious problems related to the environment. Cs2SnI6 perovskite has been known to be synthesized in a simple chemical process and it can be produced on a large scale. Moreover, this material is also oxygen and moisture stable due to the high oxidation state of tin. In this study, we synthesize air-stable Cs2SnI6 perovskite by the use of the wet chemical process at room temperature. Next, we attempt to fabricate the inverted bulk heterojunction solar cells incorporated Cs2SnI6 as electron transport layer in the configuration of ITO/ZnO/Cs2SnI6/P3HT:PCBM/PEDOT:PSS/Ag to improve device performance. The Cs2SnI6 perovskite shows an Fm-3m space group with a cubic lattice parameter of 11.62Å confirmed by X-Ray Diffraction (XRD) measurement, while UV-Vis measurement indicates this type of perovskite has direct band gap ~3.1 eV. The fabricated solar cell device reveals the enhancement in current density at short circuit condition (Jsc) from 64.69 mA/cm2 to 77.02 mA/cm2 with the addition of 2.25 mg/ml Cs2SnI6 along with the enhancement of power conversion efficiency (PCE) from 7.05% to 9.75% as characterized by J-V measurement. In our case, the voltage at open circuit condition (Voc) of the device does not perform significant improvement. Besides, it is found that the solar cell devices are quite stable even after exposure in the air for six weeks after fabrication, as indicated by PCE performance.

Nickel oxide (NiOx) film is employed to replace PEDOT:PSS as the hole transport layer for the inverted perovskite solar cells (PSCs) with Zinc Oxide as electron transport layer, and we focus on the...

The mismatch of the energy level between electron transport layer (ETL) and perovskite film (PS) is one of the origins of current-voltage (J-V) hysteresis in perovskite solar cells (PSCs). Drift-di...

PCBM is a fullerene derivative, which is commonly employed as an electron transport layer (ETL), and still has some issues to fabricate low temperature-processed perovskite solar cells (PSCs) such as surface trap states, low electron mobility, and extra recombination losses at the perovskite/PCBM interface. Herein, a novel perylene diimide dimer (2FBT2FPDI) is synthesized and employed as an ETL or intermediary layer to overcome these challenges. Owing to its suitable energy levels and high electron mobility, 2FBT2FPDI shows great potential to serve as a promising efficient ETL in the photovoltaic devices. Moreover, 2FBT2FPDI can coordinate with the lead site of the perovskite surface, which helps to heal the surface defects and suppress charge-trapped recombination. Therefore, the performance of PSCs is greatly improved from 17.3 to 20.3%, when 2FBT2FPDI was used as the intermediary layer to assist the growth of the PCBM film. This work presents a new direction through interface engineering with n-type nonfullerene small molecules for low temperature-processed stable and highly efficient inverted PSCs.

Organic-inorganic lead halide perovskites are promising materials for realization of low-cost and high-efficiency solar cells. Because of the toxicity of lead, Sn-based perovskite materials have been developed as alternatives to enable fabrication of Pb-free perovskite solar cells. However, the solar cell performance of Sn-based perovskite solar cells (Sn-PSCs) remains poor because of their large open-circuit voltage (

The use of LiF as a thin interlayer between the electron transport layer and cathode has played a pivotal role in remarkable advances in perovskite LEDs (PeLEDs); however, the mechanism behind the effect of LiF remains to be fully understood. Here, we report a combined experimental and computational study, from which we ascribe the benefits of a LiF interlayer to the migration of dissociated Li into the cathode and dissociated F into the anode. Electronic device simulations reveal that the former improves electron injection by lowering the Schottky barrier height, while the latter reduces the barrier width. These reduce turn-on voltage and improve current density and charge balance in LEDs. We fabricate PeLEDs with and without the LiF interlayer and link these materials and electronic phenomena to the device light-current-voltage characteristics. X-ray photoelectron spectroscopy obtained in sputter profiling of PeLEDs corroborates the dissociation of LiF.

The electrical character and interface contact of the electron transport layer (ETL) play a critical role in high-efficiency planar perovskite solar cells. Here, a dual functional surface alkali-ga...

The structure-dependent thermal stability of fullerene electron transport layers (ETLs) and its impact on device stability have been underrated for years. Based on cocrystallographic understanding, herein, we develop a thermally stable ETL comprising a hybrid layer of [6,6]-phenyl-C

Choline chloride as a photosynthesis promoter is important for increasing plant yield, and we have found that it has a similar effect in perovskite solar cells (PSCs). Here, we propose the innovati...

SnO2 has been proven to be an effective electron transport layer (ETL) material for perovskite solar cells (PSCs) owing to its excellent electrical and optical properties. Here, we introduce a viable spray coating method for the preparation of SnO2 films. Then, we employ a SnO2 film prepared using the spray coating method as an ETL for PSCs. The PSC based on the spray-coated SnO2 ETL achieves a power conversion efficiency of 17.78%, which is comparable to that of PSCs based on conventional spin-coated SnO2 films. The large-area SnO2 films prepared by spray coating exhibit good repeatability for device performance. This study shows that SnO2 films prepared by spray coating can be applied as ETLs for stable and high-efficiency PSCs. Because the proposed method involves low material consumption, it enables the low-cost and large-scale production of PSCs.

To extract charges more efficiently through charge-transporting layers (CTLs), various dopants are necessary. Lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) is the most widely used dopant in ...

A high‐quality electron transport layer (ETL) is a critical component for the realization of high‐efficiency perovskite solar cells. We developed a controllable direct‐contact reaction process to prepare a chlorinated SnO2 (SnO2‐Cl) ETL. It is unique in that (a) 1′2‐dichlorobenzene is used to provide more reactive Cl radicals for more in‐depth passivation; (b) it does not introduce any impurities other than chlorine. It is found that the chlorine modification significantly improves the electron extraction. Consequently, its associated solar cell efficiency is increased from 17.01% to 17.81% comparing to the pristine SnO2 ETL without the modification. The hysteresis index is significantly reduced to 0.017 for the SnO2‐Cl ETL.

A major problem in the application of mesoporous TiO2 as an electron transport layer for flexible perovskite solar cells is that a high-temperature sintering process is required to remove organic a...

Titanium oxide (TiO2) is commonly used as an electron transport layer (ETL) of regular-structure perovskite solar cells (PSCs); however, it suffers from inherent drawbacks such as low electron mobility and a high density of trap states. Modifying the surface chemistry of TiO2 has proved facile and efficient in enhancing key electron-transport properties, thereby improving device performance. In this review, we summarize recent progress on the surface modification of TiO2 in planar PSCs. The functions of different modifiers in improving device performance are elucidated, revealing the influence of modifier chemical and electronic structure on the properties of TiO2. This offers new opportunities to exploit novel materials for modifying TiO2 toward high-efficiency PSCs.

The design of electron transport layers (ETLs) with good optoelectronic properties is one of the keys to the improvement of the power conversion efficiencies (PCEs) and stability of perovskite solar cells (PSCs). Titanium dioxide (TiO2), one of the most widely used ETL in PSCs, is characterized by low electrical conductivity that increases the series resistance of PSCs, thus limiting their PCEs. In this work, we incorporated tin oxide (SnO2) into titanium dioxide (TiO2) and studied the evolution of its microstructural and optoelectronic properties with SnO2 loading. The thin films were then integrated as ETLs in a regular planar Formamidinium (FA)-rich mixed lead halide PSCs so as to assess the overall effect of SnO2 incorporation on their charge transport and Photovoltaic (PV) characteristics. Analysis of the fabricated PSCs devices revealed that the best performing devices; based on the ETL modified with 0.2 proportion of SnO2; had an average PCE of 17.35 ± 1.39%, which was about 7.16% higher than those with pristine TiO2 as ETL. The improvement in the PCE of the PSC devices with 0.2 SnO2 content in the ETL was attributed to the improved electron extraction and transport ability as revealed by the Time Resolved Photoluminescence (TRPL) and Electrochemical Impedance Spectroscopy (EIS) studies.