awn

The first observation of negative differential resistance in surface-supported metal-organic framework (SURMOF) heterojunctions is reported. The effect is created by employing a defect-engineering approach, by controlling humidity and applied electric field. The peak-to-valley current ratio of 2 is obtained at low-voltages (<2 V). The effect is applied to realize a low-voltage ternary inverter, a prototype multivalued logic device with three distinct logic states.

Abstract

The advances of surface-supported metal-organic framework (SURMOF) thin-film synthesis have provided a novel strategy for effectively integrating metal-organic framework (MOF) structures into electronic devices. The considerable potential of SURMOFs for electronics results from their low cost, high versatility, and good mechanical flexibility. Here, the first observation of room-temperature negative differential resistance (NDR) in SURMOF vertical heterojunctions is reported. By employing the rolled-up nanomembrane approach, highly porous sub-15 nm thick HKUST-1 films are integrated into a functional device. The NDR is tailored by precisely controlling the relative humidity (RH) around the device and the applied electric field. The peak-to-valley current ratio (PVCR) of about two is obtained for low voltages (<2 V). A transition from a metastable state to a field emission-like tunneling is responsible for the NDR effect. The results are interpreted through band diagram analysis, density functional theory (DFT) calculations, and ab initio molecular dynamics simulations for quasisaturated water conditions. Furthermore, a low-voltage ternary inverter as a multivalued logic (MVL) application is demonstrated. These findings point out new advances in employing unprecedented physical effects in SURMOF heterojunctions, projecting these hybrid structures toward the future generation of scalable functional devices.

Solid additives are demonstrated to enhance the initial device efficiency as well as the operational lifetime of nonfullerene organic solar cells, via solid-additive-mediated aggregation control.

Abstract

The additive strategy is widely used in optimizing the morphology of organic solar cells (OSCs). The majority of additives are liquid with high boiling points, which will be trapped within device and consequently deteriorate performance during operation. In this work, solid but volatile additives 2-(4-fluorobenzylidene)-1H-indene-1,3(2H)-dione (INB-F) and 2-(4-chlorobenzylidene)-1H-indene-1,3(2H)-dione (INB-Cl) are designed to replace the common 1,8-diiodooctane (DIO) in nonfullerene OSCs. These additives present during solution casting but evaporate after moderate heating. Molecular dynamics simulations show that they can reduce the adsorption energy to improve π-π stacking among nonfullerene acceptor (NFA) molecules, an effect that enhances light absorption and electron mobility. Both INB-F and INB-Cl enhance efficiency, with INB-F achieving a maximum efficiency of 16.7% from 15.1% of the reference PBDB-T-2F (PM6):BTP-BO-4F (Y6-BO) cell, and outperforming DIO. Remarkably, they can simultaneously enhance the operational stability, with the INB-F-treated OSC maintaining over 60% of the initial efficiency after 1000 h operation, demonstrating a T ₈₀ lifetime of 523 h, which is a significant improvement over T ₈₀ values of 66.2 h for the reference and 6.6 h for DIO-treated OSC. The simultaneously enhanced efficiency and operational lifetime are also effective in PM6:BTP-BO-4Cl (Y7-BO) OSCs, demonstrating a universal strategy to improve the performance of OSCs.

Spectral conversion using luminescent materials is an emerging strategy to enhance the light-harvesting efficacy of dye-sensitized photovoltaics (DSPV). Herein, downconversion (dc) SrF₂:Pr³⁺−Yb³⁺ nanophosphor as an optical filter and amplifier demonstrating tuned luminescence (green and red emitting) is utilized effectively under both the indoor and outdoor applications. The dc-DSPV realizes a maximum efficiency of ≈16% under indoor low-light condition.

Luminescent nanophosphors as spectral converters offer immense potential for dye-sensitized photovoltaics (DSPV) to harvest a wide range of the solar spectrum. Herein, a novel structural design of DSPV using a downconversion (dc) nanophosphor layer in the TiO₂ photoanode for both indoor (ambient) and outdoor applications is demonstrated. Cubic SrF₂:Pr³⁺−Yb³⁺ nanoparticles are synthesized by a template-free hydrothermal technique. The dc nanophosphor absorbs photons of the blue region, leading to emission of a broad luminescence band (green and red), which is well matched with N719-dye absorption. The mixed-valence state of Pr ions (Pr³⁺ and Pr⁴⁺) leads to trap-assisted transition levels, which result in a broad visible emission. For the first time, a unique Pr³⁺−Yb³⁺ codoped dc system yielding tuned and intensified luminescence by effective crossrelaxation (CR) with a back energy transfer (BET) mechanism is designed and efficient working of the dc nanophosphor-layered DSPVs under both outdoor 1 sun (AM 1.5 G) and indoor light (Warm-3200 K; Day-5000 K) conditions is demonstrated. Improved efficiency of 9.07% is attained in dc-dye-sensitized solar cells (DSSC) compared with a control-DSSC (8.39%) at 1 sun intensity. Under indoor low-light conditions (1000 lux), the dc-DSPV achieves high power conversion efficiencies (PCEs) of 14.85 and 15.9%, respectively. This approach results in a 63.44% increment in output power density for dc-DSPV compared with the control-DSPV under LED 3200 K irradiation. These findings suggest that this configuration of dc-layered DSPV can provide a new strategy for future indoor electronic operations under ambient light conditions.

Integrating a thin bulk-heterojunction layer composed of the typical poly (3-hexylthiophene-2,5-diyl) and [6,6]-phenyl methyl C61 butyric acid methyl ester (P3HT:PCBM) in a carbon-based all inorganic CsPbIBr₂ perovskite solar cell can effectively suppress interfacial energy loss and greatly improve the power conversion efficiency from 8,87% to 11.54%, which is also at the highest efficiency level of the reported counterparts.

The CsPbIBr₂ perovskite has obvious advantages in balancing the stability and efficiency in inorganic perovskite solar cells (PSCs). Its large bandgap of 2.08 eV, which leads to a narrow spectral absorption (<600 nm), is the key limit to yielding a high power conversion efficiency (PCE). Herein, it is demonstrated that by integrating a thin bulk-heterojunction (BHJ) layer (19 nm) composed of the typical poly (3-hexylthiophene-2,5-diyl) and [6,6]-phenyl methyl C61 butyric acid methyl ester (P3HT:PCBM) with CsPbIBr₂ perovskite, a carbon-based all-inorganic PSC achieves a much higher champion PCE (11.54%) than the original CsPbIBr₂ device (8.87%), and the value is also at the highest PCE level of all-inorganic CsPbIBr₂ PSCs. The integration of a thin BHJ layer brings an expanded light absorption range, better charge transfer dynamics, suppressed interfacial energy loss, and improved long-term stability. The unencapsulated CsPbIBr₂ PSC with an integrated BHJ layer shows excellent long-term stability in an ambient atmosphere with high relative humidity (RH ≈ 45%, T ≈ 25 °C). Therefore, the BHJ integration is an effective strategy on the road to industrialization of carbon-based all-inorganic PSCs with low cost, high efficiency, and excellent long-term stability.

Further large-scale photovoltaic deployment mandates the reduction of scarce Ag, typically comprising the metallic contact of solar cells. Electrodeposited Cu contacts are demonstrated for the first time on single-junction FA_0.75Cs_0.25Pb(I_0.8Br_0.2)₃ perovskite solar cells (PSCs) using an atomic layer deposition (ALD) Al₂O₃ masking layer on ITO. The stable photoconversion efficiency after Cu²⁺ reduction confirms that PSCs can survive wet-chemical plating process.

Electroplated copper contacts on small-area single-junction perovskite solar cells (PSCs) using an atomic layer deposited (ALD) Al₂O₃ masking layer on ITO are demonstrated for the first time. The photoconversion efficiency of ≈11% after manufacturing the Cu contacts confirms that PSCs can survive the wet-chemical plating process. From the successful realization of plated contact fingers, the creation of an electrical contact between the Cu electrode and the ITO on the FA_0.75Cs_0.25Pb(I_0.8Br_0.2)₃ perovskite absorber is inferred. Furthermore, scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) analysis shows the formation of a compact interface between ITO and plated Cu. An additional plating approach, using self-passivated aluminum as mask, allows to produce well-defined 30 μm wide Cu contacts on the PSC. Such a plating process allows for plating a low-resistive Cu grid simultaneously on both sides of a perovskite silicon heterojunction tandem solar cell with TCO, independent of substrate size.

The effect of absorber stoichiometry in wide-gap ACIGS solar cells is revised. A strong and opposing effect on J _SC and V _OC is found. With increasing [I]/[III] values > 0.9, V _OC continuously decreases, while charge carrier collection increases. Observations can be explained by decreasing absorber doping toward stoichiometric composition. The results indicate a very low diffusion length in wide-gap ACIGS films.

The effect of absorber stoichiometry in (Ag,Cu)(In,Ga)Se₂ (ACIGS) solar cells with bandgaps (E _g) > 1.40 eV is studied on a large sample set. It is confirmed that moving away in composition from ternary AgGaSe₂ by simultaneous reduction in Ga and Ag content widens the chalcopyrite single-phase region and thereby reduces the amount of ordered vacancy compounds (OVCs). As a consequence, a distortion in current−voltage characteristics, ascribed to OVCs at the back contact, can be successfully avoided. A clear anticorrelation between open-circuit voltage (V _OC) and short-circuit current density (J _SC) is detected with varying absorber stoichiometry, showing decreasing V _OC and increasing J _SC values for [I]/[III] > 0.9. Capacitance profiling reveals that the absorber doping gradually decreases toward stoichiometric composition, eventually leading to complete depletion. It is observed that only such fully depleted samples exhibit perfect carrier collection, evidencing a very low diffusion length in wide-gap ACIGS films. The results indicate that OVCs at the surface play a minor or passive role for device performance. Finally, a solar cell with V _OC = 0.916 V at E _g = 1.46 eV is measured, which is, to the best of our knowledge, the highest value reported for this bandgap to date.

Publication date: 15 September 2021

Source: Joule, Volume 5, Issue 9

Author(s): Zhenyu Chen, Wei Song, Kuibao Yu, Jinfeng Ge, Jinsheng Zhang, Lin Xie, Ruixiang Peng, Ziyi Ge

Publication date: 15 September 2021

Source: Joule, Volume 5, Issue 9

Author(s): Pengqing Bi, Shaoqing Zhang, Zhihao Chen, Ye Xu, Yong Cui, Tao Zhang, Junzhen Ren, Jinzhao Qin, Ling Hong, Xiaotao Hao, Jianhui Hou

Next-generation flexible solar cells have recently undergone rapid development with a promising outlook for high performance and mass-producibility. Protecting these devices from moisture and oxygen by effective encapsulation is essential to achieve the required operational lifetimes for commercialization. This article reviews flexible barrier materials and encapsulation strategies to improve the lifetime of flexible perovskite and organic photovoltaics.

Abstract

Perovskite solar cells (PSCs) and organic photovoltaics (OPVs) have undergone rapid development within the last decade, exhibiting exciting properties such as high efficiency, flexibility, and the potential for large-scale fabrication through roll-to-roll (R2R) processing. Despite this, operational stability is recognized to be an ongoing challenge as prolonged device lifetimes are scarcely observed. This instability can be narrowed down to both “intrinsic degradation” and “extrinsic degradation,” with exposure to moisture and oxygen having detrimental effects on device performance. A means of delaying the degradation of flexible PSC and OPV devices is through barrier encapsulation. Despite glass encapsulation exhibiting ideal barrier properties, the potential for flexible devices and high-throughput R2R fabrication requires the development of flexible barrier materials and encapsulation strategies. These barriers must demonstrate outstanding moisture permeation resistance, high transparency, chemical and thermal stability, and must be able to withstand repeated mechanical deformation. Herein, the fundamental principles of PSC and OPV devices are initially discussed, highlighting the degradation mechanisms and current stability obstacles. A review of the latest flexible barrier materials and encapsulation strategies follows, introducing stability studies that have been undertaken on flexible PSCs and OPV, along with suggestions as to the direction that future research may take.

Current losses in perovskite solar cells (PSCs) are investigated using transient photoluminescence and charge extraction measurements. Mobile ions cause a substantial current and efficiency loss by accumulating at the perovskite/transport layer interfaces, which screens the internal electric field. This work elucidates the detrimental impact of mobile ions in PSCs and paves the path toward mitigating this key loss mechanism.

Abstract

Efficient mixed metal lead-tin halide perovskites are essential for the development of all-perovskite tandem solar cells, however they are currently limited by significant short-circuit current losses despite their near optimal bandgap (≈1.25 eV). Herein, the origin of these losses is investigated, using a combination of voltage dependent photoluminescence (PL) timeseries and various charge extraction measurements. It is demonstrated that the Pb/Sn-perovskite devices suffer from a reduction in the charge extraction efficiency within the first few seconds of operation, which leads to a loss in current and lower maximum power output. In addition, the emitted PL from the device rises on the exact same timescales due to the accumulation of electronic charges in the active layer. Using transient charge extraction measurements, it is shown that these observations cannot be explained by doping-induced electronic charges but by the movement of mobile ions toward the perovskite/transport layer interfaces, which inhibits charge extraction due to band flattening. Finally, these findings are generalized to lead-based perovskites, showing that the loss mechanism is universal. This elucidates the negative role mobile ions play in perovskite solar cells and paves a path toward understanding and mitigating a key loss mechanism.

A thiadiazole-based polymer donor (PB2F) with an ultradeep highest occupied molecular orbital level and high electroluminescence is reported. In organic solar cell (OSC) devices, PB2F exhibits a power conversion efficiency (PCE) of 14.5% after blending with IT-4F, one of highest values among the IT-4F-based OSCs, and an outstanding PCE of 18.6% in the context of ternary OSC.

Abstract

Under the premise of ensuring favorable bulk heterojunction morphology in organic solar cells (OSCs), conjugated polymer donors with deep-lying highest occupied molecular orbital (HOMO) levels are highly important to improve power conversion efficiencies (PCEs) by reducing photovoltage loss. However, the development of such materials has lagged. Herein, a thiadiazole-based conjugated polymer, PB2F is reported, which has a very deep HOMO level of −5.64 eV, and high electroluminescence quantum efficiency of 3.9 × 10⁻³. In OSCs, the PB2F-based OSC gives an excellent PCE of 14.5% with an ultrahigh open-circuit voltage (V _OC) of 0.957 V by blending with an electron acceptor of IT-4F. More importantly, the PB2F as a third component is added into the PBDB-TF:BTP-eC9 blend to achieve an outstanding PCE of 18.6% (certified PCE 18.2%), which is one of the highest PCEs in OSCs.

Although organic photovoltaics have been established to be a promising candidate for indoor light recycling, standardized testing conditions to quantify their performance are still lacking. Therefore, a method to calculate the efficiency of solar cells on the basis of relative emission spectra, quantum efficiency and current-density-voltage measurements, which enables a fair ranking of champion solar cells, is proposed.

Abstract

With increasing efficiencies of non-fullerene acceptor-based organic solar cells, thin-film technology is becoming a promising candidate for indoor light harvesting applications. However, the lack of standardized comparison methods makes it difficult to quantify progress and to compare indoor performance. Herein, a simple method to calculate the efficiency of solar cells under any possible light source and illuminance with only using simple standard measurements (current–voltage curves and quantum efficiency) is presented. Thereby, equal evaluation conditions are ensured, so that indoor solar cells can be ranked and compared according to their efficiency. Efficiencies are shown to typically vary by ±20% when using different different light emitting diode spectra with color temperatures ranging from 2700 to 6500 K. Calculations based on a detailed balance model indicate that the optimal bandgap of the absorber material depends on the used light source and ranges between 1.75 and 2 eV. The approach is validated by comparison with literature data and many calculated efficiencies match well with experimental data obtained with a specific light source. However, some reported efficiencies cannot be reproduced with the model, which highlights the need to reassess low light measuring techniques. Furthermore, a script is provided for use by the community.

A versatile co-evaporation approach to create perovskites layers with graded energy levels favorable for different device architectures is demonstrated. The p-i-n perovskite solar cells, incorporating co-evaporated MAPbI₃ with customized graded Fermi levels, achieve power conversion efficiency over 20% with different hole transporting layers and champion values of 20.6%, 19.1%, and 17.2% for 0.086, 1, and 1.96 cm² active areas, respectively.

Abstract

Recent progress of vapor-deposited perovskite solar cells (PSCs) has proved the feasibility of this deposition method in achieving promising photovoltaic devices. For the first time, it is probed the versatility of the co-evaporation process in creating perovskite layers customizable for different device architectures. A gradient of composition is created within the perovskite films by tuning the background chamber pressure during the growth process. This method leads to co-evaporated MAPbI₃ film with graded Fermi levels across the thickness. Here it is proved that this growth process is beneficial for p-i-n PSCs as it can guarantee a favorable energy alignment at the charge selective interfaces. Co-evaporated p-i-n PSCs, with different hole transporting layers, consistently achieve power conversion efficiency (PCE) over 20% with a champion value of 20.6%, one of the highest reported to date. The scaled-up p-i-n PSCs, with active areas of 1 and 1.96 cm², achieved the record PCEs of 19.1% and 17.2%, respectively, while the flexible PSCs reached a PCE of 19.3%. Unencapsulated PSCs demonstrate remarkable long-term stability, retaining ≈90% of their initial PCE when stored in ambient for 1000 h. These PSCs also preserve over 80% of their initial PCE after 500 h of thermal aging at 85 °C.

A high-performance photodetector based on an all-inorganic CsPbBr₃ perovskite nanocrystals/2D non-layered cadmium sulfide selenide heterostructure is demonstrated through energy band engineering with designed typed-II heterostructure. Compared with pure CsPbBr₃ NCs and 2D-non-layered cadmium sulfide selenide devices, the responsivity of the heterostructure photodetector is enhanced by 406 times and 59 times, and the detectivity is improved over 700% and 1100%, respectively.

Abstract

Perovskites have attracted intensive attention as promising materials for the application in various optoelectronic devices due to their large light absorption coefficient, high carrier mobility, and long charge carrier diffusion length. However, the performance of the pure perovskite nanocrystals-based device is extremely restricted by the limited charge transport capability due to the existence of a large number of the grain boundary between perovskite nanocrystals. To address these issues, a high-performance photodetector based on all-inorganic CsPbBr₃ perovskite nanocrystals/2D non-layered cadmium sulfide selenide heterostructure has been demonstrated through energy band engineering with designed typed-II heterostructure. The photodetector exhibits an ultra-high light-to-dark current ratio of 1.36 × 10⁵, a high responsivity of 2.89 × 10² A W⁻¹, a large detectivity of 1.28 × 10¹⁴ Jones, and the response/recovery time of 0.53s/0.62 s. The enhancement of the optoelectronic performance of the heterostructure photodetector is mainly attributed to the efficient charge carrier transfer ability between the all-inorganic CsPbBr₃ perovskites and 2D cadmium sulfide selenide resulting from energy band alignment engineering. The charge carriers’ transfer dynamics and the mechanism of the CsPbBr₃ perovskites/2D non-layered nanosheets interfaces have also been studied by state-state PL spectra, fluorescence lifetime imaging microscopy, time-resolved photoluminescence spectroscopy, and Kelvin probe force microscopy measurements.

The suitability of substrate materials for co-evaporated perovskite solar cells is commonly assessed via heuristic approaches. Here, a universal guideline for the choice of substrate material is developed by investigating the thin-film formation of co-evaporated perovskite absorbers on various substrate materials. The guideline enables a targeted screening of substrate materials based on their surface characteristics enabling efficient all-evaporated perovskite solar cells.

Abstract

Vacuum-based deposition of optoelectronic thin films has a long-standing history. However, in the field of perovskite-based photovoltaics, these techniques are still not as advanced as their solution-based counterparts. Although high-efficiency vacuum-based perovskite solar cells reaching power conversion efficiencies (PCEs) above 20% are reported, the number of studies on the underlying physical and chemical mechanism of the co-evaporation of lead iodide and methylammonium iodide is low. In this study, the impact of one of the most crucial process parameters in vacuum processes—the substrate material—is studied. It is shown that not only the morphology of the co-evaporated perovskite thin films is significantly influenced by the surface polarity of the substrate material, but also the incorporation of the organic compound into the perovskite framework. Based on these studies, a selection guide for suitable substrate materials for efficient co-evaporated perovskite thin films is derived. This selection guide points out that the organic vacuum-processable hole transport material 2,2″,7,7″-tetra(N,N-di-p-tolyl)amino-9,9-spirobifluorene is an ideal candidate for the fabrication of efficient all-evaporated perovskite solar cells, demonstrating PCEs above 19%. Furthermore, building on the insights into the formation of the perovskite thin films on different substrate materials, a basic crystallization model for co-evaporated perovskite thin films is suggested.

A general and effective strategy is delivered to modulate the 2D/3D microstructure of tin-perovskite films by introduction of a 2D phase with the function of FPEABr, which induces high-orientation growth of 3D FASnI₃ by embracing the 3D grains at their surfaces and boundaries. That leads to a breakthrough of device performance of 14.81% in power conversion efficiency, along with 14.03% certified.

Abstract

As the most promising lead-free one, tin-halides based perovskite solar cells still suffer from the severe bulk-defect due to the easy oxidation of tin from divalent to tetravalent. Here, a general and effective strategy is delivered to modulate the microstructure of 2D/3D heterogeneous tin-perovskite absorber films by substituting FAI with FPEABr in FASnI₃. The introduction of 2D phase can induce highly oriented growth of 3D FASnI₃ and it is revealed in the optimal 2D/3D film that 2D phase embraces 3D grains and locates at the surfaces and grain boundaries. The FPEA⁺ based 2D tin-perovskite capping layer can offer a reducing atmosphere for vulnerable 3D FASnI₃ grains. The unique microstructure effectively suppresses the well-known oxidation from Sn²⁺ to Sn⁴⁺, as well as decreasing defect density, which leads to a remarkable enhanced device performance from 9.38% to 14.81% in conversion efficiency. The certified conversion efficiency of 14.03% announces a new record and moves a remarkable step from the last one (12.4%). Besides of this breakthrough, this work definitely paves a new way to fabricate high-quality tin-perovskite absorber film by constructing effective 2D/3D microstructures.

Three 2,6-diphenylpyridine-3,5-dicarbonitrile-based compounds with excellent photoluminescent quantum yields (79–100%) and high horizontal dipole ratios (86−88%) in the thin films are demonstrated. With two methyl groups on the triarylamines, the spin−orbit coupling is enhanced due to the elevated locally excited triplet states (³LE), leading to a fast reverse intersystem crossing. Green thermally activated delayed fluorescence (TADF) organic light-emitting diodes based on them exhibit a record-high external quantum efficiency of 39.8% without any optical extraction technique.

Abstract

Highly efficient thermally activated delayed fluorescence (TADF) molecules are in urgent demand for solid-state lighting and full-color displays. Here, the design and synthesis of three triarylamine-pyridine-carbonitrile-based TADF compounds, TPAPPC, TPAmPPC, and tTPAmPPC, are shown. They exhibit excellent photoluminescence quantum yields of 79−100% with small ΔE _ST values, fast reverse intersystem crossing (RISC), and high horizontal dipole ratios (Θ_// = 86−88%) in the thin films leading to the enhancement of device light outcoupling. Consequently, a green organic light-emitting diode (OLED) based on TPAmPPC shows a high average external quantum efficiency of 38.8 ± 0.6%, a current efficiency of 130.1 ± 2.1 cd A^–1, and a power efficiency of 136.3 ± 2.2 lm W^–1. The highest device efficiency of 39.8% appears to be record-breaking among TADF-based OLEDs to date. In addition, the TPAmPPC-based device shows superior operation lifetime and high-temperature resistance. It is worth noting that the TPA-PPC-based materials have excellent optical properties and the potential for making them strong candidates for TADF practical application.

Flexible and stretchable solar cells are important for a range of emerging applications such as electronic skins, e-textiles, wearable displays and health sensors, among others. An overview of stretchable optoelectronics is provided, where the benefits of stretchable solar cells are addressed, and the progress made in this field in terms of efficiency and strategies to achieve mechanical stretchability are underlined.

Abstract

Emerging forms of soft, flexible, and stretchable electronics promise to revolutionize the electronics industries of the future offering radically new products that combine multiple functionalities, including power generation, with arbitrary form factor. For example, skin-like electronics promise to transform the human-machine-interface, but the softness of the skin is incompatible with traditional electronic components. To address this issue, new strategies toward soft and wearable electronic systems are currently being pursued, which also include stretchable photovoltaics as self-powering systems for use in autonomous and stretchable electronics of the future. Here recent developments in the field of stretchable photovoltaics are reviewed and their potential for various emerging applications are examined. Emphasis is placed on the different strategies to induce stretchability including extrinsic and intrinsic approaches. In the former case, engineering and patterning of the materials and devices are key elements while intrinsically stretchable systems rely on mechanically compliant materials such as elastomers and organic conjugated polymers. The result is a review article that provides a comprehensive summary of the progress to date in the field of stretchable solar cells from the nanoscale to macroscopic functional devices. The article is concluded by discussing the emerging trends and future developments.

A hydrophobic p-type semiconducting additive, fluorinated-gold-clusters, is used as a bifunctional interfacial mediator to efficiently modulate the carrier dynamics of perovskite and restrain the perovskite from degradation by external environmental stimuli, which results in an n–i–p perovskite solar cell with a champion efficiency up to 24.02% and moisture stability over 10 000 h in relative humidity of 75%.

Abstract

Tackling the interfacial loss in emerged perovskite-based solar cells (PSCs) to address synchronously the carrier dynamics and the environmental stability, has been of fundamental and viable importance, while technological hurdles remain in not only creating such interfacial mediator, but the subsequent interfacial embedding in the active layer. This article reports a strategy of interfacial embedding of hydrophobic fluorinated-gold-clusters (FGCs) for highly efficient and stable PSCs. The p-type semiconducting feature enables the FGC efficient interfacial mediator to improve the carrier dynamics by reducing the interfacial carrier transfer barrier and boosting the charge extraction at grain boundaries. The hydrophobic tails of the gold clusters and the hydrogen bonding between fluorine groups and perovskite favor the enhancement of environmental stability. Benefiting from these merits, highly efficient formamidinium lead iodide PSCs (champion efficiency up to 24.02%) with enhanced phase stability under varied relative humidity (RH) from 40% to 95%, as well as highly efficient mixed-cation PSCs with moisture stability (RH of 75%) over 10 000 h are achieved. It is thus inspiring to advance the development of highly efficient and stable PSCs via interfacial embedding laser-generated additives for improved charge transfer/extraction and environmental stability.