Quantum Dot Solar Cells Research Articles

Germylene Mediated Reductive C−C and C−N Coupling of an Isocyanide and its Device Application

AbstractWe have demonstrated a unique reductive coupling of 4‐iodophenyl isocyanide, facilitated by a perimidine‐based N‐heterocyclic germylene (NHGe), which yields a bis‐spirogerma compound featuring simultaneous C−C and C−N bond formation. This reaction, which leads to the oxidation of germanium from +2 to +4, represents a significant departure from previously documented isocyanide‐germylene interactions. The product exhibits extensive conjugation across its bicyclic C4Ge2N2 framework, conferring distinct photophysical properties, including prominent orange luminescence in both solution and solid states. The photophysical properties are supported by the TD‐DFT calculations confirming an n→π* transition. The potential application of this compound in optoelectronic devices, particularly as a hole transport layer in PbS quantum dot solar cells, is also explored, with promising preliminary results.

Germylene Mediated Reductive C-C and C-N Coupling of an Isocyanide and its Device Application.

We have demonstrated a unique reductive coupling of 4-iodophenyl isocyanide, facilitated by a perimidine-based N-heterocyclic germylene (NHGe), which yields a bis-spirogerma compound featuring simultaneous C-C and C-N bond formation. This reaction, which leads to the oxidation of germanium from +2 to +4, represents a significant departure from previously documented isocyanide-germylene interactions. The product exhibits extensive conjugation across its bicyclic C4Ge2N2 framework, conferring distinct photophysical properties, including prominent orange luminescence in both solution and solid states. The photophysical properties are supported by the TD-DFT calculations confirming an n→π* transition. The potential application of this compound in optoelectronic devices, particularly as a hole transport layer in PbS quantum dot solar cells, is also explored, with promising preliminary results.

Numerical study of P3HT-based hybrid solid-state qantum dot solar cells with CdS quantum dots employing different metal oxides using SCAPS-1D

This study presents a comprehensive numerical investigation into solid-state quantum dot solar cells (SSQDSCs) utilizing P3HT poly(3-hexylthiophene) as both a hole transport and absorber layer employing SCAPS-1D simulation software, the research explores the performance of cells composed of FTO (Fluorine-doped Tin Oxide) as the front contact, integrated with different metal oxides (Titanium dioxide (TiO2), zinc oxide (ZnO), and tin dioxide (SnO2), CdS (Cadmium sulfide )quantum dots, P3HT, and Pt (platinum )as the back contact namely Hybrid solar cell. The thickness of each layer is systematically optimized, and the influence of various CdS quantum dots sizes is thoroughly examined. The study also dived into the characterization of interface defects at the P3HT/CdS junction, involving modifications to the electron affinity of P3HT. Additionally, the impact of metal work function variations was also investigated analyzing at each case critical parameters such as open-circuit voltage (VOC), short-circuit current density (JSC), fill factor (FF), power conversion efficiency (PCE) and quantum efficiency. The results demonstrate that optimization of these parameters has the potential to elevate solar cell efficiency to 18%. These simulation findings offer valuable insights for comparative analysis and a deeper understanding of the challenges encountered in experimental research.

Interface-resolved photovoltage generation dynamics and band structure evolution in a PbS quantum dot solar cell.

For directed development of solar cells using nanomaterials such as quantum dots, there is a need to understand the device function in detail. Understanding where photovoltage is generated in a device and where energy losses occur is a key aspect of this, and development of methods which can provide this information is needed. We have previously shown that time-resolved photoelectron spectroscopy of core levels can be used to follow the photovoltage dynamics at a specific interface of a lead sulfide quantum dot solar cell. Here, we use the method's selectivity and sample design to investigate the photovoltage generation in different parts of this solar cell and determine how the different layers (including the absorber layer thickness) contribute to charge separation. We show that all layers contribute to photovoltage generation and that a gold contact deposited on the quantum dots is necessary for full photovoltage generation and slow charge recombination. By combining the information obtained, we are able to experimentally follow the time evolution of the solar cell band structure during the charge separation process. Furthermore, we can identify which specific layers need to be optimized for an overall improvement of quantum dot cells. In the future, this methodology can be applied to other types of devices to provide insights into photovoltage generation mechanisms.

Optical Applications of CuInSe2 Colloidal Quantum Dots.

The distinctive chemical, physical, electrical, and optical properties of semiconductor quantum dots (QDs) make them a highly fascinating nanomaterial that has been extensively studied. The CuInSe2 (CIS) QDs demonstrates great potential as a nontoxic alternative to CdSe and PbSe QDs for realizing high-performance solution-processed semiconductor devices. The CIS QDs show strong light absorption and bright emission across the visible and infrared spectrum and have been designed to exhibit optical gain. The special characteristics of these properties are of great significance in the fields of solar energy conversion, display, and electronic devices. Here, we present a comprehensive overview of the potential applications of colloidal CIS QDs in various fields, with a particular focus on solar energy conversion (such as QD solar cells, QD-sensitized solar cells, and QD luminescence solar concentrators), solar-to-hydrogen production (such as photocatalytic and photoelectrochemical H2 production), and QD electronics (such as QD transistors, QD light-emitting diodes, and QD photodetectors). Furthermore, we offer our insights into the current challenges and future opportunities associated with CIS QDs for further research.

Enhanced carrier transfer performance on blade-coating PbS quantum dot solar cells by coordinated operation of iodine ligands

The significant breakthrough in the photovoltaic conversion efficiency of lead sulfide (PbS) quantum dot solar cells has primarily been achieved on small substrates using the spin-coating method. However, the blade-coating technique offers a scalable alternative for large-scale fabrication of absorption film, addressing the limitations of spin-coating for commercial applications. Given the inherent challenges of the blade-coating method, which often produces low-quality and defective films. Thus, an iodide ligand passivation strategy to realize the formation of high-quality films with reduced trap states was proposed. Typically, the iodide ligand is incorporated into the precursor solution with the aim of fine-tuning the nanoparticle’s functionality, facilitating the formation of systematically aligned and densely coupled film configurations during the blade coating procedure. The functional mechanisms of the aligned and compact-coupled configurations, as well as the effect of iodide introduction on defect mitigation, have been systematically investigated. The results reveal that iodide ligand introduction modulates the interparticle electrostatic potential and inter-dot space, facilitating the formation of a uniform structure with enhanced energy level alignment and reduced trap states. The highly aligned and compact structure improves interfacial integration with the ZnO electron transport layer, enabling efficient photon-electron extraction and transfer. As a result, PbS quantum dot solar cells fabricated using the blade coating technique have achieved an optimized efficiency of 4.68 %, offering significant potential for the development and production of directly-synthesized ink for quantum dot solar cells.

Additive-assisted passivating manipulation for printable carbon-based CsPbBr3 perovskite quantum dots solar cells with stacked structure

Carbon-based perovskite solar cells (PSCs) have attracted attention as low-cost and facile fabrication process. However, the ionic nature of perovskite and nonradiative recombination at perovskite/carbon interface are present inevitable obstacles in approaching their highly efficiency. Herein, the multifunctional molecules of zinc oxalate is implanted into the precursor of perovskite to passivate defects and narrowing the interface energy barrier, and a flexible method of screen-printing employed in prepare stacked structure device ITO/SnO2/CsPbBr3•x % ZnOX //CQDs/ITO. In this regard, CQDs are used as carbon electrodes to replace expensive materials of hole transport layer and precious metal electrode, in which CQDs extracted from sugarcane molasses, a cheap by-product of native sugar industry. Additionally, the stacked structure composed of a photoanode (ITO/SnO2/CsPbBr3•x % ZnOX) and back electrode (CQDs/ITO) exhibits a promising prospect in photovoltaic application. Finally, the power conversion efficiency of 2 % ZnOX modified PSCs increases to 1.96 %, and the improvement rate has reached 1.54 times. In addition, modified PSCs with a greater stability compared with that of the control device. This work presents a useful approach to passivate defects and provides a cost-effective option to fabricate devices with stacked structure.

Increase the efficiency of lead sulfide colloidal quantum dots solar cells by incorporating In2O3 and NiO interlayers

Substantial advancements have been made in PbS colloidal quantum dot solar cells (CQDSCs) by focusing on device architecture, manipulating band alignment, and refining the surface chemistry of colloidal quantum dots (CQDs). Nevertheless, creating an incredibly stable and efficient solar cell remains a challenging problem for researchers in this field. This study reveals that the efficiency of PbS CQDSCs can be improved by incorporating ultrathin In2O3 (between ITO electrode & indium-doped zinc oxide ETL) and NiO (between PbS-EDT HTL and Au electrode) nanocrystalline interlayers. The enhanced power conversion efficiency (PCE), which increases from 11.5 % to 13.6 %, is attributed to the improved surface smoothness and well-matched energy bandgap. Furthermore, following a heating period of 90 min at a temperature of 80 °C and 50 days of storage in the air, the solar cells containing these interlayers retained 98 % and 99 % of their initial efficiency, respectively. In distinction, the control device without these interlayers maintained only 85 % and 91 % of their initial efficiency under identical testing environments.

ZnO/SrTiO3, ZnO/WO3, and ZnO/Zn2SnO4 Bilayer as Electron Transport Layers for Lead Sulfide Colloidal Quantum Dots Solar Cells.

In order to enhance the overall efficiency of colloidal quantum dots solar cells, it is crucial to suppress the recombination of charge carriers and minimize energy loss at the interfaces between the transparent electrode, electron transport layer (ETL), and colloidal quantum dots (CQDs) light-absorbing material. In the current study, ZnO/SrTiO3(STO), ZnO/WO3(TO), and ZnO/Zn2SnO4(ZTO) bilayers are introduced as an ETL using a spin-coating technique. The ZTO interlayer exhibits a smoother surface with a root-mean-square (RMS) value of ≈ 3.28nm compared to STO and TO interlayers, which enables it to cover the surface of the ITO/ZnO substrate entirely and helps to prevent direct contact between the CQDs absorber layer and the ITO/ZnO substrate, thereby effectively preventing efficient charge recombination at the interfaces of the ETL/CQDs. Furthermore, the ZTO interlayer possesses superior electron mobility, a higher visible light transmission, and a suitable energy band structure compared to STO and TO. These characteristics are advantageous for extracting charge carriers and facilitating electron transport. The PbS CQDs solar cell based on the ITO/ZnO/ZTO/PbS-FABr/PbS-EDT/NiO/Au device configuration exhibits the highest efficiency of 15.28%, which is significantly superior than the ITO/ZnO/PbS-FABr/PbS-EDT/NiO/Au solar cell device (PCE = 14.38%). This study is anticipated to offer a practical approach to develop ultrathin and compact ETL for highly efficient CQDSCs.

Rare earth Nd3+-doped organic-inorganic hybrid perovskite quantum dots for white LED

Lead halide perovskite quantum dots (QDs) have garnered significant attention due to their tunable band gaps, unique quantum confinement effects, and high photoluminescence quantum yields (PLQYs). Among them, Organic-inorganic QDs make them promising candidates for optoelectronic devices such as quantum dot light-emitting diodes (QLEDs), solar cells, lasers, and photodetectors. However, the toxicity of lead (Pb) has raised environmental and health concerns, hindering their industrial application. To alleviate concerns about heavy metals Pb, extensive research has been conducted on B-site doping and the development of lead-free perovskites. Herein, we firstly developed B-site doping strategy on organic-inorganic hybrid perovskite QDs via rare-earth elements. Neodymium (III) (Nd3+) doped FAPbBr3 QDs were prepared through the ligand-assisted reprecipitation method at room temperature. The B-site doping strategy could alleviate the heavy metal problem of Pb and modulate the band gap of FAPbBr3 QDs facilely. The results demonstrated that increasing the concentration of Nd³⁺ can change the emission of FAPbBr₃ QDs from pure green to deep blue. Specifically, we achieved highly pure blue emission (∼438 nm) with a full width at half maximum (FWHM) of 13 nm for Nd³⁺-doped FAPbBr₃ QDs. Time-resolved photoluminescence (TRPL) spectroscopy revealed a decrease in the lifetime of FAPbBr₃ QDs from 22.86 to 15.46 ns as the doping concentration increased. Additionally, we fabricated a white LED (WLED) utilizing blue-emitting Nd³⁺-doped FAPbBr₃, green-emitting FAPbBr₃ QDs, and red QDs, achieving a white emission color coordinate of (0.33, 0.36). This study pioneers the application of B-site rare-earth doping in organic-inorganic hybrid perovskite QDs, demonstrating that B-site composition engineering is a reliable strategy to further exploit the perovskite family for wider optoelectronic applications.

Tailoring Energy Structure of Low‐Toxic Ternary Ag−Bi−S Quantum Dots through Solution‐Phase Synthesis for Quantum‐Dot‐Sensitized Solar Cells

AbstractLow‐toxic multinary semiconductor quantum dots (QDs) showing a photoresponse in a wide wavelength range from visible to near‐IR wavelength regions have been intensively investigated for fabricating efficient solar light conversion systems. Recently, AgBiS2 QDs have attracted much attention for their application to improve the performance of QD solar cells because they have a large absorption coefficient in the visible and near‐IR regions. In this report, we describe solution‐phase preparation of ternary Ag−Bi−S QDs with different sizes and with different Ag/Bi ratios. The average size of resulting spherical Ag−Bi−S QDs was controllable from 2.7 to 8.1 nm by adjusting the reaction temperature from 373 to 473 K, while the Ag fraction of obtained QDs also increased with an increase in particle size. The absorption onset wavelength shifted from 850 to 1200 nm in the near‐IR region as the particle size increased. AgBiS2 QDs with an almost stoichiometric composition, obtained at reaction temperatures of 423 K and 473 K, contained no deep intragap states and exhibited a p‐type semiconductor behavior, while QDs prepared at a reaction temperature of 393 K or lower had non‐stoichiometric Ag‐deficient compositions producing intragap defect states. Sensitized solar cells fabricated with stoichiometric AgBiS2 QDs exhibited a photoresponse in visible and near‐IR wavelength regions, the optimal PCE being 0.74% with AgBiS2 QDs of 6.2 nm in diameter that were prepared at 423 K.

Efficiency optimization of All-Inorganic perovskite solar cell device using NiOx and ZnO as charge transport layers

In this study, we have developed and refined an all-inorganic perovskite solar cell with the structure FTO/ZnO/CsPbBr3/NiOx/Au. This was accomplished by incorporating the inorganic perovskite CsPbBr3 and the inorganic charge transport layers ZnO and NiOx. We employed solvent engineering techniques such as dropping solvents like isopropyl alcohol (IPA) and ethyl acetate (EA) during the spin-coating process, along with optimizing the thickness of the absorber layer and annealing conditions to enhance the power conversion efficiency (PCE). Our evaluation of the impact of the CsPbBr3 absorption layer thickness on PCE revealed that efficiency improved with layer thicknesses up to 280 nm. Moreover, we investigated the influence of post-deposition annealing durations on CsPbBr3, experimenting with times of 0.5hr, 1hr, 2hr, 3hr, and 5hr. The optimal conversion efficiency of 0.91 % was attained with an annealing temperature of 225 °C for 2hr, particularly when the absorption layer thickness was set at 280 nm. These results suggest that the device structure optimization for all-inorganic perovskite quantum dot solar cells can be successfully applied for efficiency optimization.

Correlation between Photoluminescence Features and Enhanced Performance in Formamidinium Lead Triiodide Quantum Dot Solar Cells by Replacement of Octadecene

In this study, an innovative approach is developed for fabricating formamidinium lead triiodide (FAPbI3) quantum dots (QDs) by substitution of octadecene (ODE). The results showcase the formation of superior‐quality FAPbI3 QD films, boasting enhanced photoluminescence (PL) and transport properties. Specifically, ODE has been replaced with octene (OCE), a shorter linear alpha olefin. Comparisons are drawn between the novel synthesis method and the conventional ODE‐based QD films, scrutinizing their optical properties and applicability in QD solar cells. The outcomes highlight distinctions in temperature‐dependent PL emission characteristics, revealing an unprecedented absolute PL QY of up to 84%, a notable improvement from the 70% achieved with ODE, along with enhanced transport properties. Furthermore, the performance of both systems in QD solar cells is evaluated for two values of layer thickness, 100 and 200 nm, to investigate the transport properties at the device level. The results exhibit a remarkable improvement from 200% to 150% in average power conversion efficiency (PCE) and consistently higher values for open‐circuit voltage and short‐circuit current density for the OCE‐based solar cell compared to an ODE‐based counterpart for both thickness values, reaching a striking 6.7% PCE for the best‐performing device despite the nonideal conditions.

Surface Engineering Enables Efficient AgBiS2 Quantum Dot Solar Cells.

Surface ligand chemistry is vital to control the synthesis, diminish surface defects, and improve the electronic coupling of quantum dots (QDs) toward emerging applications in optoelectronic devices. Here, we successfully develop highly homogeneous and dispersed AgBiS2 QDs, focus on the control of interdot spacing, and substitute the long-chain ligands with ammonium iodide in solution. This results in improved electronic coupling of AgBiS2 QDs with excellent surface passivation, which greatly facilitates carrier transport within the QD films. Based on the stable AgBiS2 QD dispersion with the optimal ligand state, a homogeneous and densely packed QD film is prepared by a facile one-step coating process, delivering a champion power conversion efficiency of approximately 8% in the QD solar cells with outstanding shelf life stability. The proposed surface engineering strategy holds the potential to become a universal preprocessing step in the realm of high-performance QD optoelectronic devices.

Perovskite Quantum Dots for Solar Cells and Beyond

Halide perovskite solar cells have witnessed great successes recently while their instability is a big hurdle for practical application. Herein we discuss our recent progress in addressing the stability of perovskite solar cells, including introduction of capping layers to improve the stability against moisture and heat, and perovskite size engineering to suppress phase segregation. In particular, quantum dots (QDs) have the advantages of quantum confinement effect, defect-tolerant nature, and processability for flexible devices. We discuss a new surface ligand engineering strategy in designing new hybrid perovskite QDs with controllable compositions and sizes The QDs have been used as building blocks in quantum dot solar cells delivering a certified record efficiency of 16.6% with excellent long-term operation stability. By using QDs as light absorbing materials, the QD based photocatalysts also exhibited good stable performance in photocatalytic hydrogen production. The combination of perovskite QDs with Metal-Organic Framework (MOF) materials to form new composites led to ultrastable photoluminescent property for > 10,000 hours. The integration of perovskite solar cells and rechargeable batteries have led to a single module type rechargeable solar batteries with an overall storable solar energy conversion efficiency of >12%.

(Digital Presentation) Cooperative Quantum Dynamics of Excitons in Colloidal Quantum Dots for Novel Optoelectronic Applications

Colloidal semiconductor quantum dots (QDs) are excellent materials for combining photonics and nanoscience. They have been extensively studied to understand the photophysics of quantum confined excitons and to develop efficient optoelectronic devices such as QD solar cells and light-emitting diodes. The photophysical processes of QD devices are governed by a large number of QDs constructing the devices. Therefore, cooperative quantum dynamics of QDs, i.e., synchronous responses of QD ensembles, have a great potential for boosting optoelectronic device performances.Before the use of cooperative quantum dynamics in QD devices, the understanding of quantum dynamics of excitons, i.e., coherent properties of multiexcitons, is required to draw out quantum cooperativity from QD ensembles. In order to elucidate coherent dynamics of multiexcitons during resonant laser-pulse excitation, we performed a quantum interference spectroscopy of QD responses. We found that multiexcitons generate the high-frequency coherent oscillations with integer multiples of the exciton resonance frequency, which is called harmonic quantum coherence, and that the coherent responses govern the microscopic processes in the resonant multiphoton absorption [1-3]. Furthermore, it was demonstrated that the coherent responses were detectable as photocurrent signals in thin films of QD ensembles [4]. These developments build up an essential base of quantum cooperativities emerging in optoelectronics.Here, we report recent investigations of cooperative quantum dynamics in QDs. In optoelectronic devices, electronic couplings between QDs are expected to generate a new type of quantum cooperativities. To generate electronic coupling, we fabricated closely packed PbS QDs by using a ligand exchange method. We found that nonlinear photocurrent signals are strongly enhanced in the QD solids. The comparison analysis of different ligands clarified that the enhancement ratio increases monotonically with the decrease of the inter-QD distance [5]. This means that the signal enhancement originates from the electronic coupling and cooperative behavior of QDs. These findings show that the cooperative quantum dynamics provide a new route to advanced optoelectronic technology such as nonlinear amplifiers.Part of this work was supported by JSPS KAKENHI (JP19H05465, JP22H01990, and JP23K17877), JST PRESTO (JPMJPR23H3), and JST CREST (JPMJCR21B4).

(Invited) Parameter Prediction in Colloidal Quantum Dot Solar Cells Using Residual Neural Networks Trained on Experimental Data

Colloidal quantum dots (CQDs) are an attractive third-generation material for photovoltaics, especially as infrared materials for multi-junction solar cells. Characterization and materials parameter prediction both play a critical role in the rising efficiencies in this field. However, there are numerous materials properties that need to be measured in order to fully characterize a device, leading to high research costs and slow development times. Here, we leverage recent advancements in machine learning (ML), along with a recently-demonstrated multimodal spectral characterization method [1], to predict complex materials parameters in CQD solar cells from simple current density-voltage (JV) curves, using an algorithm trained on experimental data.[2]Past work ML prediction of materials properties has focused on using simulated data due to the difficulty in collecting enough experimental data to fully train an algorithm. While it is not feasible to fabricate thousands of devices in a typical research lab, it is possible to measure several thousand points on a single device. We used a micrometer-resolution 2D characterization method with millimeter-scale field of view to acquire enough training data using only a handful of devices, while learning the spatial relationships between materials parameters. Photoluminescence, trap state density, transient photovoltage, transient photocurrent, and carrier mobility were predicted (Figure 1) by five different residual neural networks, each using a ResNet block and containing over 300k learnable parameters. The design of the networks were based on the ResNet50 architecture [3]. We also implemented a novel neighborhood approach to reduce errors and account for spatial correlations in device behavior, leading to insights into transport mechanisms and correlation lengths in CQD thin films. This method could be used to study a wide range of material systems and devices, ultimately leading to a universal prediction model that greatly simplifies the characterization process for optoelectronic devices and accelerates development times.

The Effect of Quantum Dots on the Performance of the Solar Cell

Quantum dot solar cells are currently the subject of research in the fields of renewable energy, photovoltaics and optoelectronics, due to their advantages which enables them to overcome the limitations of traditional solar cells. The inability of ordinary solar cells to generate charge carriers, which is prevents them from contributing to generate the current in solar cells. This work focuses on modeling and simulating of Quantum Dot Solar Cells based on InAs/GaAs as well as regular type of GaAs p-i-n solar cells and to study the effect of increasing quantum dots layers at the performance of the solar cell. The low energy of the fell photons considers as one of the most difficult problems that must deal with. According to simulation data, the power conversion efficiency increases from (12.515% to 30.94%), current density rises from 16.4047 mA/cm2 for standard solar cell to 39.4775 mA/cm2) using quantum dot techniques (20-layers) compared to traditional type of GaAs solar cell. Additionally, low energy photons' absorption range edge expanded from (400 to 900 nm) for quantum technique. The results have been modeled and simulated using (SILVACO Software), which proved the power conversion efficiency of InAs/GaAs quantum dot solar cells is significantly higher than traditional (p-i-n) type about (247%)

Hybrid Thin Film Encapsulation for Improving the Stability of PbS Quantum Dot Solar Cells.

The instability to moisture, heat, and ultraviolet (UV) light is the main problem in the application of quantum dot solar cells (QDSCs). Thin film encapsulation can effectively improve their operational stability. However, it is difficult to achieve multiple barrier effects with single layer of encapsulated film. Here, a hybrid thin-film encapsulation strategy is reported to encapsulate lead sulfide QDSCs, which can isolate moisture and partial thermal, and prevent the penetration of UV light, thus retarding the surface oxidation process of the quantum dots. After 60h, the encapsulated device retains a normalized power conversion efficiency of 83.8% and 80.6% at 85% humidity and 75 °C, respectively, which is three and six times of the value obtained in unencapsulated devices. At continuous UV illumination, encapsulated device exhibits five times higher stability than the reference. This strategy provides the way for the overall improvement of the operating stability of lead sulfide QDSCs in harsh environments of high humidity, high temperature, and UV light.

Phenylethylammonium bromide-assisted solution-phase ligand exchange in CsPbBr3 quantum dot solar cells

CsPbBr3 quantum dots (QDs) have excellent optical properties and good phase stability, but the long-chain ligands on their surfaces affect the charge transfer between QDs. Here, we propose a simple ligand exchange strategy: solution-phase ligand exchange. By adding an acetone solution of phenylethylammonium bromide to the purification process of CsPbBr3 QDs, the long-chain ligands were effectively replaced and the electric coupling between QDs was improved. As a result, the power conversion efficiency of the solar cell was increased from 1.95% to 2.83%. Meanwhile, the stability of the devices was significantly improved in the unencapsulated case.