awn

In article number 2001509, Cheng‐Liang Liu and coworkers demonstrate the scalable ultrasonic spray‐coating method combined with ternary channel pumping of precursor solutions and vacuum‐assisted thermal annealing to fabricate large‐area MAPbI_3−x Br _x mixed halide perovskite films of size 7 × 10 cm². Eight subcells are obtained with a champion and average PCE of 17.11% and 16.25 ± 0.77%, respectively.

Solid oxide fuel cell oxygen electrode is improved by introducing a nanocrystalline interlayer of electrochemically active oxide between the electrolyte and oxygen electrode. Active interfacial layers are fabricated by spray pyrolysis technique. The microstructure and crystallization of the active interfacial layer are investigated. The symmetrical cells and solid oxide cells with active interfacial layer show an improved electrochemical performance.

Abstract

Intermediate temperature solid oxide fuel cells oxygen electrodes are modified by active interfacial layers. Spray pyrolysis is used to produce thin (≈500 nm) layers of mixed ionic and electronic conductors: Sm_0.5Sr_0.5CoO_{3− δ} (SSC), La_0.6Sr_0.4CoO_{3− δ} (LSC), La_0.6Sr_0.4Co_0.2Fe_0.8O_{3− δ} (LSCF), and Pr₆O₁₁ (PrO _x ) on the electrode–electrolyte interface. The influence of the annealing temperature on the electrode polarization (area specific resistance—ASR_pol) is investigated by impedance spectroscopy of symmetrical electrodes in the temperature range of 400–700 °C. The results show that the introduction of nanocrystalline interlayers promotes an oxygen reduction reaction by extending the active surface area and improved contact between the electrode and the electrolyte. Introducing LSCF, LSC, or SSC interlayer reduces ASR_pol by a factor of 4 and PrO _x by a factor of 2 against the reference, powder processed LSCF electrode. At 600 °C, the obtained ASR_pol values for PrO _x , LSCF, LSC, and SSC interlayer are 245, 137, 119, and 107 mΩ cm², which can be considered very low in comparison to standard powder processed oxygen electrodes. Anode supported single cell with developed LSC/LSCF electrode reveals ≈1.2 W cm⁻² power output at 600 °C and maintains stable cell voltage of 0.75 V under 1 A cm⁻² during 60 h of the test.

A multi‐cation halide composition of perovskite solar cells is engineered via a two‐step sequential deposition method by adding mixtures of 1D polymorphs of orthorhombic δ‐RbPbI₃ and δ‐CsPbI₃ to the PbI₂. This approach greatly facilitates heterogeneous nucleation which leads to perovskite with high crystallinity and superior optoelectronic properties. Solar cells fabricated with these perovskites exhibit an efficiency of over 22%.

Abstract

The performance of perovskite solar cells is highly dependent on the fabrication method; thus, controlling the growth mechanism of perovskite crystals is a promising way towards increasing their efficiency and stability. Herein, a multi‐cation halide composition of perovskite solar cells is engineered via the two‐step sequential deposition method. Strikingly, it is found that adding mixtures of 1D polymorphs of orthorhombic δ‐RbPbI₃ and δ‐CsPbI₃ to the PbI₂ precursor solution induces the formation of porous mesostructured hexagonal films. This porosity greatly facilitates the heterogeneous nucleation and the penetration of FA (formamidinium)/MA (methylammonium) cations within the PbI₂ film. Thus, the subsequent conversion of PbI₂ into the desired multication cubic α‐structure by exposing it to a solution of formamidinium methylammonium halides is greatly enhanced. During the conversion step, the δ‐CsPbI₃ also is fully integrated into the 3D mixed cation perovskite lattice, which exhibits high crystallinity and superior optoelectronic properties. The champion device shows a power conversion efficiency (PCE) over 22%. Furthermore, these devices exhibit enhanced operational stability, with the best device retaining more than 90% of its initial value of PCE under 1 Sun illumination with maximum power point tracking for 400 h.

Thin-film, cover, and hybrid encapsulation technologies, that function as a moisture and oxygen permeation barrier and mechanical protection to prevent leakage of toxic by-product, and limit decomposition of reactants in a confined space, can be applied in organic light emitting diodes, organic and perovskite solar cells, leading to robust stability and long lifetime in three types of devices.

Abstract

Organic light emitting diodes (OLEDs) employing organic thin-film based emitters have attracted tremendous attention due to their widespread applications in lighting and as displays in mobile devices and televisions. The novel thin-film photovoltaic techniques using organic or organic–inorganic hybrid materials such as organic photovoltaics (OPVs) and perovskite solar cells (PSCs) have become emerging competitive candidates with regard to the traditional photovoltaic techniques on account of high-efficiency, low-cost, and simple manufacturing processing properties. However, OLEDs, OPVs, and PSCs are vulnerable to the undesired degradation induced by moisture and oxygen. To afford long-term stability, a robust encapsulation technique by employing materials and structures that possess high barrier performance against oxygen and moisture must be explored and employed to protect these devices. Herein, the recent progress on specific encapsulation materials and techniques for three types of devices on the basis of fundamental understanding of device stability is reviewed. First, their degradation mechanisms, as well as, influencing factors are discussed. Then, the encapsulation technologies and materials are classified and discussed. Moreover, the advantages and disadvantages of various encapsulation technologies and materials coupled with their encapsulation applications in different devices are compared. Finally, the ongoing challenges and future perspectives of encapsulation frontier are provided.

Publication date: July 2021

Source: Nano Energy, Volume 85

Author(s): Difei Zhang, Wenkai Zhong, Lei Ying, Baobing Fan, Meijing Li, Ziqi Gan, Zhaomiyi Zeng, Dongcheng Chen, Ning Li, Fei Huang, Yong Cao

Drop-on-demand inkjet-printing has the advantages of high cost-effectiveness and powerful patterning ability. In this work, a simple inkjet-printing method is developed to prepare perovskite films under ambient condition, where the effects of precursor ink, substate conditions, and printing parameters on the morphology and microstructure of the printed perovskite films have been systematically investigated.

Drop-on-demand inkjet-printing has the advantages of high cost-effectiveness and powerful patterning ability, which can be a promising technique for perovskite pattern deposition. However, by far most of the reported works using inkjet-printing for perovskite films fabrication are printing solvent-rich wet precursor layers on the high-temperature meso-TiO₂ substrate, and subsequently require a vacuum-assisted thermal annealing process to enhance the crystallization of perovskite precursor, which largely elevates fabrication cost and process complexity. Herein, a heat-assisted inkjet-printing process is developed to directly print compact and uniform crystalline perovskite films on the planar PEDOT:PSS substrate under ambient condition. The effects of precursor composition, printing temperature, solvent system, and, especially, the printing parameters on the final morphology and microstructure of the printed perovskite films are systematically studied for the first time and the related crystal growth models are revealed, which provide a constructive guidance for the future studies on ambient inkjet-printed perovskite films and devices. Based on these studies, a champion power conversion efficiency (PCE) of 16.6% for the ambient printed PSC devices is achieved. This work provides a reliable and cost-effective approach for the scalable fabrication of perovskite films with a low material consumption.

Polymer Solar Cells

In article number 2000673, Hyeok Kim and co‐workers used indium gallium zinc oxide (IGZO), which is mainly used as an oxide TFT of a display panel and applied it as an electron extraction layer of a polymer solar cell. As the era of flexible displays approaches, the era when flexible polymer solar cell modules can be used will also come quickly.

Transparent Photovoltaics

In article number 2000564, Shun‐Wei Liu and co‐workers demonstrated vacuum‐deposited transparent photovoltaics with a power conversion efficiency of 1.34%, average visible transmission of 77.45%, and a color rendering index of 91.9. Such see‐through solar technology not only provides a solution to convert ambient light (sunlight or indoor lights) to electricity, but also offers the realization of self‐sustainable power.

Thin‐Film Solar Cells

In article number 2000524, Yue Yang and co‐workers propose a composite light‐trapping structure with a double‐layer antireflection coating on the upper surface and Ag hemispheres on the substrate to achieve full‐spectrum absorption enhancement in a‐Si:H thin‐film solar cells. The short‐circuit current density and photoelectric conversion efficiency are improved by ∽40% compared to a 100‐nm‐thick bare cell and increasing the cell thickness to 400 nm could even approach the theoretical absorption limit.

Perovskite Solar Cells

In article number 2000621, Wei Wang, Zongping Shao, and co‐workers introduced a gentle butyl acrylate additive into MAPbI₃‐based perovskite solar cells to enhance the efficiency and stability by improving perovskite film quality, constructing suitable energy level alignment and increasing charge carrier lifetime. Consequently, the device with butyl acrylate additive delivers a high power conversion efficiency of 20.0% and superior moisture/thermal stability under ambient conditions.

Ultrathin Solar Cells

In article number 2000534, José M. V. Cunha and co‐workers applied two SiO_x passivation architectures in ultrathin CIGS solar cells. Both passivation approaches resulted in devices with a higher performance compared to a reference non‐passivated device. The potential to use SiO_x as passivation material, deposited by a high throughput industrial technique based in microelectronics processing, yields promising results towards high‐performance low‐cost ultrathin CIGS solar cells.

Passivating the defects and preventing the degradation of metal halide perovskites by humidity continues to pose a big challenge to the vast scientific community developing this promising new light harvesting material. In this review, recent advances and prospects employing organic ammonium halide-based passivation materials that attempt to suppress such issues in n–i–p architecture perovskite solar cells are discussed.

Abstract

Despite rapid improvements in efficiency, long-term stability remains a challenge limiting the future up-scaling of perovskite solar cells (PSCs). Although several approaches have been developed to improve the stability of PSCs, applying ammonium passivation materials in bilayer configuration PSCs has drawn intensive research interest due to the potential of simultaneously improving long-term stability and boosting power conversion efficiency (PCE). This review focuses on the recent advances of improving n-i-p PSCs photovoltaic performance by employing ammonium halide-based molecular modulators. The first section briefly summarizes the challenges of perovskite materials by introducing the degradation mechanisms associated with the hygroscopic nature and ion migration issues. Then, recent reports regarding the roles of overlayers formed from ammonium-based passivation agents are discussed on the basis of ligand and halide effects. This includes both the formation of 2D perovskite films as well as purely organic passivating layers. Finally, the last section provides future perspectives on the use of organic ammonium halides within bilayer-architecture PSCs to improve the photovoltaic performances. Overall, this review provides a roadmap on current demands and future research directions of molecular modulators to address the critical limitations of PSCs, to mitigate the major barriers on the pathway toward future up-scaling applications.

The operational lifetimes of UV‐absorbing organic solar cells based on contorted hexabenzocoronene (cHBC) and its derivatives are systematically investigated. In contrast to highly stable reference cells, devices based on halogenated cHBCs as acceptors show rapid degradation with development of S‐shaped J–V curves. The introduction of halogenation on cHBC can affect thin‐film morphological stability and thus device lifetime.

Abstract

Transparent photovoltaics that harvest ultraviolet photons are promising point‐of‐use power sources for lower power applications, such as electrochromic windows that regulate the flow of visible and infrared photons for lighting and temperature regulation. Organic photovoltaic cells employing contorted hexabenzocoronene (cHBC) and its derivatives as chromophores have shown promise for transparent solar cells due to their high open‐circuit voltages, large‐area scalability, and high photoactive layer transparency. Here, the operational stability of such devices is investigated and it is found that the solar cell active layers that include peripherally halogenated chromophores undergo rapid morphological degradation during operation, while control cells employing cHBC and other non‐halogenated derivatives as donors with archetype C₇₀ as an acceptor are highly stable. This study suggests halogenation of chromophores can play an outsized role in determining the operational stability of devices comprising them, which should be considered during the molecular design process.

The potential of wide bandgap perovskite solar cells is often limited by low open‐circuit voltages. By tuning the lowest‐unoccupied molecular‐orbital of electron transport layers via the use of different fullerenes and fullerene blends, open‐circuit voltages exceeding 1.35 V in CH₃NH₃Pb(I_0.8Br_0.2)₃ device without loss in fill factor leading to a high V _oc FF product of 1.10 V are demonstrated.

Abstract

Nonradiative recombination processes are the biggest hindrance to approaching the radiative limit of the open‐circuit voltage for wide bandgap perovskite solar cells. In addition to high bulk quality, good interfaces and good energy level alignment for majority carriers at charge transport layer‐absorber interfaces are crucial to minimize nonradiative recombination pathways. By tuning the lowest‐unoccupied molecular‐orbital of electron transport layers via the use of different fullerenes and fullerene blends, open‐circuit voltages exceeding 1.35 V in CH₃NH₃Pb(I_0.8Br_0.2)₃ device are demonstrated. Further optimization of mobility in binary fullerenes electron transport layers can boost the power conversion efficiency as high as 18.9%. It is noted in particular that the V _oc fill factor product is >1.096 V, which is the highest value reported for halide perovskites with this bandgap.

A novel IDTT‐based small molecule (SM) additive (IDTT‐ThCz) is developed and introduced into perovskite solar cells (PSCs) through an anti‐solvent engineering method. This IDTT‐ThCz passivates defect states of perovskite layers, providing efficient charge extraction as well as preventing the decomposition of perovskite crystals. Therefore, IDTT‐ThCz treated PSCs achieve a highest efficiency of 22.5% and remarkable thermal stability.

Abstract

Although perovskite solar cells (PSCs) have attracted enormous attention owing to their fascinating optoelectronic properties and solution processability, defects in PSCs, which adversely affect efficiency and stability, are still not completely resolved. Herein, a novel indacenodithieno[3,2‐b]thiophene‐based small molecule (SM) additive (IDTT‐ThCz), capable of interacting with perovskite layers, is developed. In particular, the IDTT‐ThCz, which can perform a surface passivation, is introduced into the perovskite layer to significantly suppress perovskite defects via antisolvent treatment. Furthermore, this facile surface passivation not only significantly improves the charge extraction capability, but also prevents perovskite degradation. The IDTT‐ThCz‐treated PSCs exhibits a power conversion efficiency (PCE) of 22.5% and retains 95% of its initial PCE after 500 h storage under thermal condition (85 °C), representing the most remarkable efficiency as well as stability among the SM additives reported to date.

Bottom-surface defect passivation of perovskite film is enabled by covalently attaching –OH to a hole-transporting polymer. A solvent evaporation-induced self-assembly of the resultant amphiphilic hole-transporting polymer enriches –OH on the film surface, passivating defects of the upper perovskite layer. Inverted perovskite solar cells based on this polymer afford an efficiency of 20.12% with improved device stability compared to its poly(bis(4-phenyl)(2,5,6-trimethylphenyl)amine) counterpart.

Abstract

Bottom-surface defect passivation of perovskite film, lagging far behind easily conducted bulk and top-surface passivations in perovskite solar cells (PSCs), remains rather challenging because most passivation molecules/groups can be eroded by polar solvents used for the subsequent perovskite deposition. In this work, an effective bottom-surface passivation is enabled for enhanced performance of inverted PSCs by covalently attaching a passivation group (hydroxyl) to a hole transporting polymer. A short linker (methylene) between the hydroxyl and the conjugated backbone bearing hydrophobic long alkyl chains is adopted to improve the resistance of the resultant amphiphilic polymer to polar solvents. A solvent evaporation-induced self-assembly of the amphiphilic hole transporting polymer is developed to enrich hydroxyl groups on the film surface, passivating defects of the upper perovskite layer via interactions with undercoordinated Pb²⁺ and I^– sites. Inverted PSCs based on this hole transporting film are superior in efficiency (20.12%), reproducibility, large-area fabrication, and stability to its classical poly(bis(4-phenyl)(2,5,6-trimethylphenyl)amine) counterpart. This work demonstrates that rational introduction of passivation groups into the hole transporting layer combined with self-assembly-modulated component distributions is useful to realize bottom-surface passivation of the perovskite layer for improved photovoltaic performance.

A facile yet effective thioamides passivation strategy is proposed to suppress defects at the surface and grain boundary of CsSnI₃ perovskite, which reduces the deep level trap density from undercoordinated Sn²⁺ and Sn²⁺ oxidation. The surface passivated CsSnI₃ perovskite solar cell (PSC) delivers a efficiency of 8.20% which is the highest among all lead‐free all‐inorganic PSCs.

Abstract

Despite remarkable progress in hybrid perovskite solar cells (PSCs), the concern of toxic lead ions remains a major hurdle in the path towards PSC's commercialization; tin (Sn)‐based PSCs outperform the reported Pb‐free perovskites in terms of photovoltaic performance. However, it is of a particularly great challenge to develop effective passivation strategies to suppress Sn(II) induced defect densities and oxidation for attaining high‐performance all‐inorganic CsSnI₃ PSCs. Herein, a facile yet effective thioamides passivation strategy to modulate defect state density at surfaces and grain boundaries in CsSnI₃ perovskites is reported. The thiosemicarbazide (TSC) with SCN functional groups can make strong coordination interaction with charge defects, leading to enhanced electron cloud density around defects and increased vacancy formation energies. Importantly, the surface passivation can reduce the deep level trap state defect density originated from undercoordinated Sn²⁺ ion and Sn²⁺ oxidation, significantly restraining nonradiative recombination and elongating the carrier lifetime of TSC treated CsSnI₃ PSCs. The surface passivated all‐inorganic CsSnI₃ PSCs based on an inverted configuration delivers a champion power conversion efficiency (PCE) of 8.20%, with a prolonged lifetime over 90% of initial PCE, after 500 h of continuous illumination. The present strategy sheds light on surface defect passivation for achieving highly efficient all‐inorganic lead‐free Sn‐based PSCs.

Replacing Pb²⁺ cations in the lead halide perovskite with other suitable environmentally friendly metal cations can address the toxicity of lead and the structure‐induced intrinsic instability of lead halide perovskites. Moreover, it can maintain the perovskite crystal structure and excellent photoelectric properties. Herein, a systematic review summarizes recent progress of the lead‐free halide perovskite photodetectors.

Abstract

Lead halide perovskite (LHP) has been widely researched in the photovoltaic field due to its highly attractive optoelectronic properties. Among the LHP‐based devices, the detectivity of the photodetector is as high as 10¹⁵ Jones. However, their practical application is limited by the toxicity of lead in perovskite and the inherent instability induced by the perovskite structure against moisture, heat, and light. To address these issues, tremendous efforts have been made to replace Pb²⁺ with other environmentally friendly metal cations such as Sn²⁺, Bi³⁺, Cu²⁺, Sb³⁺, and Ge²⁺. Thus, considerable breakthroughs in device performance and stability using lead‐free metal halide perovskite (LFMHP) have been made in recent years. In this review, the synthesis methods and strategies are focused for enhancing the material quality and photoelectric properties of LFMHPs and the recent research progress of LFMHP‐based photodetectors is summarized. This research provides some promising perspectives for high‐performance LFMHP photodetectors to achieve a broader range of practical applications in the future.

Moisture instability and unscalable fabrication protocols remain unsolved issues that hinder the application of FACs‐based perovskite solar cells. Here, high‐quality FACsPbI₃ films are fabricated by crown ether tailoring (which chelated with Cs⁺/Pb²⁺ ions) to inhibit the moisture invasion and stabilize the a ‐phase FACsPbI₃, producing large‐area perovskite films and with solar module performance.

Abstract

FACs‐based (FA⁺, formamidinium and Cs⁺, cesium) perovskite solar cells have gained great attention due to their remarkable light and thermal stabilities toward practical application of perovskite modules. However, the moisture instability and difficulty in scalable fabrication are still the main obstacles blocking their photovoltaic applications in current status. Here, the employment of novel interaction between crown ether with metal cations is introduced to tailor the uniform growth and inhibit moisture invasion during the crystallization of α‐phase FACsPbI₃, yielding the successful synthesis of high‐quality perovskite films in a large scale. Consequently, perovskite solar cells (PSC) modules in the total area of 4 × 4 and 10 × 10 cm² are readily fabricated with respective champion efficiencies of 16.69% and 13.84% and excellent stability over 1000 h. This facile scaling‐up strategy assisted by crown ether has shown great promise for pursuing efficient and highly stable large‐area PSC modules.

Addition of dual additive of methylammonium chloride (MACl) and CsCl in the FAPbI₃ perovskite precursor solution with a molar ratio of [MACl]/[CsCl] = 2 results in a higher power conversion efficiency and better stability than the single additive, due mainly to the further reduction in trap density and increase in resistance for charge recombination.

Abstract

Additive engineering is one of the most efficient approaches to improve not only photovoltaic performance but also phase stability of formamidinium (FA)-based perovskite. Chlorine-based additives, such as methylammonium chloride (MACl), have been in general used to improve phase stability of FAPbI₃, which however often leads to loss of open-circuit voltage V _oc, accompanied by instability of the perovskite phase due to the volatile nature of the MA cation. A dual additive strategy for improving V _oc and thereby the overall efficiency are reported here. The mixing ratio of MACl to CsCl is varied from [MACl]/[CsCl] = 4 to 1, where V _oc increases with decreasing the ratio and best performance is achieved from [MACl]/[CsCl] = 2. As compared to the single source of MACl, the addition of CsCl reduces trap density and increases resistance against charge recombination, which is responsible for the increased V _oc. Moreover, defect passivation achieved by dual additive enables better stability than the single additive MACl as confirmed by long-term stability tests with unencapsulated devices for 50 days under relative humidity of about 40% at room temperature. The best power conversion efficiency of 23.22% is achieved by dual additive, which is higher than that for single additive of MACl or CsCl.

An organic small-molecule semiconductor, DPh-DNTT, can be utilized as a dopant-free hole transporting material (HTM) for highly efficient and stable inverted perovskite solar cells due to its temperature-dependent molecular orientation. By decreasing the deposition temperature, DPh-DNTT films with a dominant face-on orientation are achieved, which exhibit improved out-of-plane hole mobility and excellent perovskite device performance without the incorporation of double-edged dopants.

Abstract

Crystallized p-type small-molecule semiconductors have great potential as an efficient and stable hole transporting materials (HTMs) for perovskite solar cells (PSCs) due to their relatively high hole mobility, good stability, and tunable highest occupied molecular orbitals. Here, a thienoacene-based organic semiconductor, 2,9-diphenyldinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DPh-DNTT), is thermally evaporated and employed as the dopant-free HTM that can be scaled up for large-area fabrication. By controlling the deposition temperature, the molecular orientation is modulated into a dominant face-on orientation with π–π stacking direction perpendicular to the substrate surface, maximizing the out-of-plane carrier mobility. With an engineered face-on orientation, the DPh-DNTT film shows an improved out-of-plane mobility of 3.3 × 10⁻² cm² V⁻¹ s⁻¹, outperforming the HTMs reported so far. Such orientation-reinforced mobility contributes to a remarkable efficiency of 20.2% for CH₃NH₃PbI₃ inverted PSCs with enhanced stability. The results reported here provide insights into engineering the orientation of molecules for the dopant-free organic HTMs for PSCs.

Suppression of nonradiative recombination and enhancement of carrier transport capability are achieved via vacuum-assisted treatment of the FA_0.75MA_0.25SnI₃ perovskite layer to self-heal defects in bulk and at surface. As a result, lead-free tin-based perovskite solar cells have reached a high efficiency of 10.3% along with an improved V _OC of 0.631 V and FF of 75.5%.

Abstract

Power conversion efficiency (PCE) of lead (Pb)-free tin (Sn)-based perovskite solar cells (PVSCs) is much lower than that of their Pb-based counterparts, which is mainly attributed to large open-circuit voltage (V _OC) loss and poor fill factor (FF). In this work, a strategy via vacuum-assisted treatment of the Sn perovskite layer to self-heal defects in Sn perovskite is reported, leading to suppression of nonradiative recombination and enhancement of carrier transport capability. Using this method, a maximum PCE of 10.3% is obtained for dual FA-MA (MA = methylammonium and FA = formamidinium) cation Sn-based PVSCs with an improved V _OC of 0.631 V and FF of 75.5%. This work suggests a facile approach to finely inhibit the defects in the bulk or at interfaces for Sn-based devices and further facilitate development of highly efficient Sn-based PVSCs.