Perovskite solar cells (PSCs) have emerged as a promising class of photovoltaic devices since they combine the benefits of high efficiency beyond 20%, low material cost, as well as easy and scalable ...processing. The appropriate choice of the electron transport layer (ETL) in these devices is one crucial aspect for achieving high efficient PSCs. The conventional ETL TiO2 is not the best choice due to its relatively low conductivity and problematic photocatalytic activity. Therefore, novel ETLs have attained increasing attention and are making rapid progress and with it the further development and optimization of planar PSCs has been promoted. In this review, we start by introducing the essential functions of ETLs in planar PSCs. Next, we give an extensive description of novel ETL materials, looking at both crystalline and amorphous systems. Their emergence, development, and accompanying optimization strategies will be discussed. Additionally, we provide a brief discussion about the correlation between materials, fabrication methods, and interface related issues. In the end, we propose some prospective research subjects that will be relevant for the further development of novel ETLs.
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•The essential functions of ETLs in planar PSCs were discussed in terms of ETL-free PSCs.•We give an extensive description of novel ETL materials, looking at both crystalline and amorphous systems.•We provide a brief discussion about the correlation between materials, fabrication methods, and interface related issues.
Given that thermal stability is of considerable importance in the field of photovoltaics, inorganic perovskites have attracted numerous attempts to overcome instability caused by volatile cations in ...organic–inorganic hybrid perovskites. As always, crystallization optimization is a paramount strategy to enhance the performance of inorganic perovskite‐based solar cells. Recently, nanoconfined crystallization is regarded as a novel and effective strategy due to the absence of chemical reactions. Herein, 1D ordered mesoporous silica is introduced into inorganic perovskite precursors to facilely induce the nanoconfined crystallization. Both theoretical and experimental analyses verify that the nanoconfined crystallization is successfully triggered by the ordered mesoporous silica, fostering the formation of 1D perovskite monocrystal. In addition, the crystallization and morphology of inorganic perovskite are effectively facilitated. As a result, the nonradiative recombination is suppressed along with the distinctly reduced trap‐state density and remarkably enhanced charge transport in perovskite. Finally, the power conversion efficiencies of CsPbIBr2‐ and CsPbI3‐based solar cells are boosted from 8.67% to 10.04% and from 14.10% to 14.69%, respectively. Meanwhile, stability tests of solar cells also show enhancement using the nanoconfined crystallization. This work provides a facile, effective, and flexible crystallization modulating strategy for fabricating efficient and stable inorganic perovskite solar cells.
ZrSBA‐15 is utilized in the nanoconfined crystallization of inorganic perovskites for the optimization of lattice strain as well as the enlargement of grain size. The as‐prepared perovskite solar cells thus obtain well‐promoted power conversion efficiency (PCE).
The future of mankind holds great promise for things like the Internet of Things, personal health monitoring systems, and smart cities. To achieve this ambitious goal, it is imperative for ...electronics to be wearable, environmentally sustainable, and safe. However, large‐scale manufacture of self‐sufficient electronic systems by exploiting multifunctional materials still faces significant hurdles. Herein, multitasking aqueous printable MXene inks are reported as an additive‐free high‐capacitance electrode, sensitive pressure‐sensing material, highly conducting current collector, metal‐free interconnector, and conductive binder. By directly screen printing MXene inks, MXene‐based micro‐supercapacitors (MSCs) and lithium‐ion microbatteries (LIMBs) are delicately fabricated on various substrates. The as‐prepared MSCs exhibit ultrahigh areal capacitance of 1.1 F cm−2 and the serially connected MSCs offer a record voltage of 60 V. The quasi‐solid‐state LIMBs deliver a robust areal energy density of 154 μWh cm−2. Furthermore, an all‐flexible self‐powered integrated system on a single substrate based on the multitasking MXene inks is demonstrated through seamless integration of a tandem solar cell, the LIMB, and an MXene hydrogel pressure sensor. Notably, this integrated system is exceptionally sensitive to body movements with a fast response time of 35 ms. Therefore, this multipurpose MXene ink opens a new avenue for powering future smart appliances.
An all‐flexible MXene‐based self‐powered electronic system is demonstrated on a single substrate through seamless integration of a tandem solar cell, MXene‐based lithium‐ion microbatteries or micro‐supercapacitors, and an MXene hydrogel pressure sensor, where the multitasking MXene is fully exploited as a high‐capacitance electrode, a sensitive pressure‐sensing material, a highly conducting current collector, a metal‐free interconnector, and a conductive binder.
Slot‐die coating holds advantages over other large‐scale technologies thanks to its potential for well‐controlled, high‐throughput, continuous roll‐to‐roll fabrication. Unfortunately, it is ...challenging to control thin.film uniformity over a large area while maintaining crystallization quality. Herein, by using a high‐pressure nitrogen‐extraction (HPNE) strategy to assist crystallization, a wide processing window in the well‐controlled printing process for preparing high‐quality perovskites is achieved. The yellow‐phase perovskite generated by the HPNE acts as a crucial intermediate phase to produce large‐area high‐quality perovskite film. Furthermore, an ionic liquid is developed to passivate the perovskite surface to reduce surface defect density and to suppress carrier recombination, resulting in significantly increased efficiency to 22.7%, the highest for large‐area fabrication. The strategies are successfully extended to large‐area device fabrication, making it possible to produce a 40 × 40 mm2 module with stabilized PCE as high as 19.4%, the highest‐efficiency for a large‐area module to date.
A high‐pressure nitrogen‐extraction strategy to drive the formation of a stable intermediate for uniform perovskite crystallization and an effective passivation strategy by utilizing an ionic liquid are reported. As such, the PCEs of a small‐area PSC and a large‐area PSC module are 22.7% and 19.6% respectively, representing a high level made using a large‐area fabrication process.
Metal‐halide perovskite has emerged as an effective photovoltaic material for its high power conversion efficiency (PCE), low cost and straightforward fabrication techniques. Unfortunately, its ...long‐term operational durability, mainly affected by halide ion migration and undercoordinated Pb2+ is still the bottleneck for its large‐scale commercialization. In this work, an ionic liquid (IL) is designed to effectively cap the grain surface for improved stability and reduced trap density. More specifically, the Br− in the IL passivates the undercoordinated Pb2+ by chemically bonding to it, resulting in a thin layer of ionic‐liquid‐perovskite formed on the surface, leading to improved photovoltaic performance and better stability. Specifically, the solar cell exhibits an open‐circuit voltage of 1.192 V and PCE of 24.33% under one‐sun illumination with negligible hysteresis, and a large area (10.75 cm2) integrated module achieves PCE of 20.33%. Moreover, the bare device maintains over 90% of its initial efficiency after 700 h of aging at 65 °C. It also shows outstanding stability with only about 10% degradation after being exposed to the ambient environment for 1000 h. The superior efficiency and stability demonstrate that the present IL passivating strategy is a promising approach for high‐performance large area perovskite solar cell applications.
An ionic liquid (IL) is designed to passivate undercoordinated Pb2+ by chemically bonding to form an IL capped perovskite surface, leading to superior photovoltaic performance and operational stability. Specifically, the small solar cell (0.1 cm2) exhibits an open‐circuit voltage of 1.192 V, power conversion efficiency of 24.33%, and the large area (10.75 cm2) integrated module achieves a PCE of 20.33%.
Despite intense development of inkjet printing for scalable and customizable fabrication of power sources, one major shortcoming is the lack of eco‐friendly aqueous inks free of additives (e.g., ...toxic solvents, surfactants). Here, an aqueous printable MXene/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonic acid) (MP) hybrid ink is demonstrated that has an adjustable viscosity to directly inkjet‐print micro‐supercapacitors (MP‐MSCs) with excellent performance, seamless integration, and desirable customization, which is crucial for scalable industrialization of self‐powered integrated systems. The MP‐MSCs deliver an unprecedented volumetric capacitance of 754 F cm−3 and a remarkable energy density of 9.4 mWh cm−3, superior to previously reported inkjet‐printed MSCs. Such outstanding performance is partly attributed to highly conductive PH1000 that prevents restacking of MXene nanosheets, enabling fast electron and ion diffusion throughout the microelectrodes. Moreover, MP‐MSCs present exceptional miniaturization and superior modularization featuring high voltage output up to 36 V from 60 serially connected cells and impressive areal voltage of 5.4 V cm−2 connected in tandem. Further, a printable temperature sensor integrated with the MP‐MSC and a flexible solar cell exhibits an exceptional response of 2% and mechanical flexibility without any bias voltage input. Therefore, the MXene inks are expected to create various opportunities for miniaturization and innovative construction of flexible, self‐sustaining, energy harvesting–storing–consuming microsystems for printable electronics.
A flexible and durable self‐powered integrated system composed of a silicon film solar cell, inkjet‐printed micro‐supercapacitor and a temperature sensor, is demonstrated, where aqueous MXene/MXene/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonic acid) hybrid inks serve as microelectrodes for micro‐supercapacitors, current collector for temperature sensor, and metal‐free interconnection.
Perovskite solar cells (PSCs), have exhibited potential value for revolutionizing photovoltaic technology for space applications, and they have passed a series of tests in a simulated space ...environment. Nevertheless, the simulated space environment on land is definitely distinguished from the real‐space conditions, and the results cannot completely represent the real operating state of PSCs in space. Herein, PSCs mounted on a high‐altitude balloon are launched into near‐space and the current–voltage characteristics are measured in situ throughout the 19‐h flight, during which the PSCs are exposed directly to near‐space and experience wide temperature variation, vacuum, and strong irradiation. Thus, the diurnal performance evolution of PSCs is obtained for the first time and a possible variation mechanism is identified. The PSCs present expected stability and a champion power density of ≈12 mW cm−2 at noon, which is demonstrated as the highest result achieved in near‐space for PSCs. Additionally, despite a complex degradation process, the PSCs still deliver a high energy density comparable to that of silicon solar cells. Finally, the challenges facing the space application of PSCs are discussed. This work highlights the feasibility of PSCs in near space and provides direction for further exploration.
Perovskite solar cells (PSCs) mounted on a high‐altitude balloon are launched into near‐space. During the 19‐h flight, the PSCs are exposed directly to near space. Then, the diurnal performance evolution of PSCs is obtained for the first time, and strikingly, they deliver a high energy density comparable to that of silicon solar cells.
The applications of wide‐bandgap (WBG) perovskite solar cells (PSCs) are limited by their subpar efficiency and stability due to their high density of defects, especially those at interfaces. ...Theoretical analyses suggest a monolayer of molecules, which is of minimum thickness and, hence, minimum resistance across the interface, possessing multifunctional groups and a permanent dipole, should effectively passivate the defects and minimize energy losses at interfaces. Herein, a self‐assembled monolayer (SAM) composed of amphiphilic molecules is designed and assembled as the interface layer to reduce the energy loss and enhance interface coupling between the perovskite and hole transport layer. It is found that the SAM also builds a back surface field through a p‐type doping effect, which promotes hole extraction and suppress the carrier recombination. Consequently, a remarkable power conversion efficiency (PCE) of 20.4% in parallel with a high open‐circuit voltage up to 1.25 V is attained. Additionally, an indoor PCE of 38.7% is realized. Both are among the best in their respective categories. Moreover, an all‐perovskite tandem solar cell is configured, presenting a decent PCE of 23.2%. This work emphasizes the significance of WBG PSCs for optoelectronic applications and indicates the eminent effects of SAMs for optimization of WBG PSCs.
A self‐assembled monolayer composed of amphiphilic molecules as the interface layer to reduce the energy loss between the perovskite and hole transport layers is reported. A remarkable power conversion efficiency (PCE) of 20.4% for wide‐bandgap perovskite solar cells is attained. Additionally, excellent performance in indoor photovoltaics and tandem solar cells, with respective PCEs of 38.7% and 23.2%, are realized.
It is arduous to prepare thin charge transport layers (CTLs) of only a few nanometers in thickness for meter-sized products, particularly for commonly used solution processes. Thus, it is desirable ...to take advantages of both solution-processed perovskites and vacuum-deposited CTLs. Herein, a surface redox engineering (SRE) is proposed for vacuum-deposited NiOx to make it match with the slot-die-coated perovskite films. Not only does it eliminate the de-wetting problem of perovskite ink, but it also imparts enhanced electronic properties at buried interfaces. Consequently, high-performance PSCs are achieved with amazing stability and outstanding power conversion efficiencies of 23.4% and 21.3% for rigid and flexible devices, respectively. Furthermore, perovskite submodules of area 156 × 156 mm2 are successfully assembled with a remarkable PCE of 18.6% along with excellent stability. The SRE provides a strategy to use the advantages of both vacuum-fabricated CTLs with wet-processed perovskites for the development of large-area perovskite modules.
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•High-performance NiOx by large-area e-beam evaporation at room temperature•Facile SRE for NiOx films to make the large-area slot-die-coated PSCs•SRE mechanism is revealed by experiments and theoretical simulations•SRE strategy improves the efficiency and stability of the solar cells
Nickel oxide (NiOx) is one of the most commonly used inorganic hole transport materials in inverted perovskite solar cells (PSCs) because of its outstanding stability and optical transmittance in entire visible spectrum. Unfortunately, its hydrophobicity and oxidizability badly affect uniform preparation of large-area stable devices. Here, we report a facile surface redox engineering (SRE) for electron-beam evaporated NiOx to perfectly match the slot-die-coated large-area PSCs. This SRE strategy eliminates the local de-wetting problem of the perovskite ink and also imparts enhanced performance in electronic properties at the buried interface via modulating the NiOx surface features. Consequently, high-performance PSCs are attained with power conversion efficiencies (PCEs) of 23.4% and 21.3% for rigid and flexible devices. Furthermore, the large-area (156 × 156 mm2) perovskite submodules are successfully assembled with a remarkable PCE as high as 18.6%.
We propose a surface redox engineering (SRE) for NiOx films, which is achieved by subjecting the films to an Ar-plasma-initiated oxidation process and a Brønsted-acid-mediated reduction process. The multifunctional SRE can foster the formation of a stabilized surface state and increase the surface energy. The assembled rigid (flexible) PSCs delivered high PCEs of up to 23.4% (21.3%) with excellent stability. Furthermore, large-area (156 × 156 mm2) submodules are designed and integrated to yield PCE as high as 18.6%.
An all-in-one self-sustained integrated system composed of a Si film solar cell, spray-printed a micro-supercapacitor and a gas sensor, exhibits excellent flexibility and durability.
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...Printable micro-supercapacitors (MSCs) with remarkable versatility, customizability, high power density and long cycling lifespan, are regarded as a promising class of miniaturized power source for wearable and portable microelectronics. Herein, we demonstrate a novel Fe-based zeolitic imidazolate framework (Fe-ZIF)/graphene (FZG) heterostructure with high specific surface area and outstanding electrical conductivity for planar MSCs (FZG-MSCs) worked in a high-voltage ionic liquid gel electrolyte via a spray-printed strategy. The fully printed FZG-MSCs deliver a high areal energy density of 9.5 μWh/cm2, extraordinary cyclability, and tailored voltage/capacitance output. Furthermore, using a fully printed FZG-MSC, we seamlessly integrate a monolithically planar all-flexible self-sustained sensor system with a mounted solar cell and a printable NH3 gas sensor on the same side of single flexible substrate. The self-sustained sensor system exhibits high-sensitivity NH3 detection with a good response of 18.3% at 20 ppm and linear sensibility exposed to 2–20 ppm. Such a fully integrated system can utilize the converted solar energy stored in the MSC, and offer efficient electricity to power microelectronics whenever needed. Therefore, this contribution of printable planar device and integrated system paves a new avenue for constructing flexible microelectronics.
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