CsPbIBr2 Perovskite Solar Cells Research Articles

Impact of La doping on the optoelectronic and structural properties of CsPbIBr2 perovskite solar cell

Inorganic lead halide perovskite solar cells (IPSC) have high power conversion efficiency (PCE). Currently, heteroatom substitution is a promising method for enhancing the properties of perovskite materials and the performance of associated devices. This study outlines the production process of a perovskite solar cell made from inorganic CsPbIBr2 with a 4 % La doping. The cubic crystal structure with large grain size and small band gap energy is observed at 4 % La–CsPbIBr2. The optoelectronic and structural characteristics of CsPbIBr2 perovskite solar cells have been substantiated through various methodologies, such as the determination of space charge restricted current, examination of the photoluminescence decay profile, assessment of charge transfer resistance, and utilization of Mott Schottky analysis. The incorporation of lanthanum-doped cesium lead iodide bromide (La-doped CsPbIBr2) resulted in a notable enhancement in both the open circuit voltage (Voc), and the short circuit current density (Jsc), leading to a much higher overall efficiency of 9.89 % compared to the pristine counterpart, which exhibited an efficiency of 8.62 %.

Bifunctional interfacial engineering enabled efficient and stable carbon-based CsPbIBr2 perovskite solar cells

Carbon-based inorganic CsPbIBr2 perovskite solar cells (C-IPSC) have attracted widespread attention due to their low cost and excellent thermal stability. Unfortunately, due to the soft ion crystal nature of perovskite, inherent bulk defects and energy level mismatch at the CsPbIBr2/carbon interface limit the performance of the device. In this study, we introduced aromatic benzyltrimethylammonium chloride (BTACl) as a passivation layer to passivate the surface and grain boundaries of the CsPbIBr2 film. Due to the reduction of perovskite defects and better energy level arrangement, carrier recombination is effectively suppressed and hole extraction is improved. The champion device achieves a maximum power conversion efficiency (PCE) of 11.30% with reduces hysteresis and open circuit voltage loss. In addition, unencapsulated equipment exhibits excellent stability in ambient air.

Healing the Buried Interface by a Plant-Derived Green Passivator for Carbon-Based CsPbIBr2 Perovskite Solar Cells.

Perovskite solar cells (PSCs) have attracted extensive attention in photovoltaic applications owing to their superior efficiency, and the buried interface plays a significant role in determining the efficiency and stability of PSCs. Herein, a plant-derived small molecule, ergothioneine (ET), is adopted to heal the defective buried interface of CsPbIBr2-based PSC to improve power conversion efficiency (PCE). Because of the strong interaction between Lewis base groups (-C═O and -C═S) in ET and uncoordinated Pb2+ in the perovskite film from the theoretical simulations and experimental results, the defect density of the CsPbIBr2 perovskite film is significantly reduced, and therefore, the nonradiative recombination in the corresponding device is simultaneously suppressed. Consequently, the target device achieves a high PCE of 11.13% with an open-circuit voltage (VOC) of 1.325 V for hole-free, carbon-based CsPbIBr2 PSCs and 14.56% with a VOC of 1.308 V for CsPbI2Br PSCs. Furthermore, because of the increased ion migration energy, the detrimental phase segregation in this mixed-halide perovskite is weakened, delivering excellent long-term stability for the unencapsulated device in ambient conditions over 70 days with a 96% retention rate of initial efficiency.

Strain engineering improves the photovoltaic performance of carbon-based hole-transport-material free CsPbIBr2 perovskite solar cells.

Alkylamines with different chain lengths including n-butylamine, n-hexylamine, and n-octylamine, are applied to regulate the CsPbIBr2 perovskite film quality by strain engineering. The status of residual strains is controllably modulated, resulting in improved efficiency and stability of carbon-based hole-transport-material free CsPbIBr2 perovskite solar cells.

Impact of Ce doping on the optoelectronic and structural properties of a CsPbIBr2 perovskite solar cell.

This paper provides a detailed analysis of pure CsPbIBr2 and 4% Ce-doped CsPbIBr2 perovskite films, emphasizing their structural, optical and photovoltaic properties. X-ray diffraction confirms a predominant cubic perovskite phase in both samples, with Ce doping leading to the increased crystal size (21 nm to 32 nm). UV-vis spectroscopy reveals a reduced bandgap energy (2.2 eV to 2.1 eV) with Ce doping. Dielectric constant analysis indicates the enhanced permittivity of the Ce-doped sample, crucial for solar-cell light trapping. Energy band structure analysis demonstrates improved photovoltaic cell performance with Ce doping, yielding higher open-circuit voltage, short-circuit current, and efficiency (9.71%) compared to pure CsPbIBr2 (8.02%). Ce doping mitigates electron-hole recombination, enhancing cell stability, electron affinity, and power output. This research underscores the potential of cost-effective, efficient, and stable CsPbIBr2 perovskite solar cells.

Trimethyl Ammonium‐Assisted Interfacial Modification for Efficient and Stable Wide‐Bandgap Perovskite Solar Cells

Wide‐bandgap (WBG) perovskite solar cells (PSCs) are acknowledged as promising candidates for tandem solar cells and building photovoltaics. It is well known that cesium‐based all‐inorganic halide WBG perovskites possess the comparable optoelectronic properties as the organic–inorganic counterparts, but exhibit superior thermal stability. Among them, CsPbIBr2 is considered a feasible material for tandem solar cells after balancing the bandgap and stability of the inorganic perovskite. However, CsPbIBr2 PSCs are often subjected to drastic interfacial charge recombination especially in carbon‐based device structure derived from the chemical bonding defects (i.e., uncoordinated Pb2+) naked on CsPbIBr2 soft lattice, which dramatically limits overall efficiency of CsPbIBr2 WBG PSCs. Herein, a trimethyl ammonium salt hexyltrimethylammonium bromide is presented for CsPbIBr2/carbon interfacial modification. Benefiting from the −N+(CH3)3 passivation effect and −C6H13 hydrophobic alkyl chain, the optimal device with highly smooth morphology and sufficient charge extraction exhibits a champion power conversion efficiency of 11.24% and improved long‐term stability with 99.7% and 79.7% efficiency retention under dry air atmosphere and continuous 85 °C thermal stress, indicating the valuable potential application of the lattice solidified CsPbIBr2 WBG PSCs.

Precursor engineering enables high-performance all-inorganic CsPbIBr2 perovskite solar cells with a record efficiency approaching 13%

All-inorganic CsPbIBr2 perovskite has attracted widespread attention in photovoltaic and other optoelectronic devices because of its superior thermal stability. However, the deposition of high-quality solution-processed CsPbIBr2 perovskite films with large thicknesses remains challenging. Here, we develop a triple-component precursor (TCP) by employing lead bromide, lead iodide, and cesium bromide, to replace the most commonly used double-component precursor (DCP) consisting of lead bromide and cesium iodide. Remarkably, the TCP system significantly increases the solution concentration to 1.3 M, leading to a larger film thickness (∼390 nm) and enhanced light absorption. The resultant CsPbIBr2 films were evaluated in planar n-i-p structured solar cells, which exhibit a considerably higher optimal photocurrent density of 11.50 mA cm−2 in comparison to that of DCP-based devices (10.69 mA cm−2). By adopting an organic surface passivator, the maximum device efficiency using TCP is further boosted to a record efficiency of 12.8% for CsPbIBr2 perovskite solar cells.

Thick film high-performance carbon-based CsPbIBr2 perovskite solar cells vis nano-perovskite modified hot casting method

All-inorganic carbon-based CsPbIBr2 perovskite solar cells (PSCs) have attracted attention due to their more balanced performance and stability. The performance of the PSCs is highly dependent on the quality of the absorber films. Unfortunately, most high-performance films are prepared in a glove box and conventional preparation methods often produce perovskite films within 400 nm of thickness, which is detrimental to large area device fabrication and limits their commercial application. Here we had demonstrated a short chain ligands nano-CsPbIBr2 particles modified hot-casting method to deposit a perovskite film with thickness up to 800 nm. It was carried out by spin-coating a hot CsPbIBr2 precursor solution onto nano-CsPbIBr2 particles film on an electron transport layer (ETL), and then depositing nano-CsPbIBr2 particles on the precursor film again before annealing. The nano-CsPbIBr2 particles on the ETL promotes precursor solution crystallization and increased film thickness, and the nano-CsPbIBr2 particles on the precursor film promoted grain growth and reduced defects due to compositional deviations from stoichiometric ratios. The power conversion efficiency (PCE) of the PSCs fabricated by this method is up to 10.66 %. The unencapsulated PSCs still retain more than 85 % of the initial PCE when stored at ambient atmosphere (RH 50–60 %) for 10 days.

Efficient all-inorganic CsPbIBr2 perovskite solar cells with an open voltage over 1.33 V by dual-additive strategy

The internal non-radiative recombination and high trap-state density (Ntrap) in perovskite layer have severely limited the progress of low-temperature processed CsPbIBr2 perovskite solar cells (PSCs). In this work, cesium acetate (CsAc) and hydrogen lead triiodide (HPbI3) dual-additives are employed to tune the properties of CsPbIBr2 film prepared by low-temperature process. The CsAc material is used to modify CsPbIBr2 surface and optimize the CsPbIBr2/carbon electrode interface, while HPbI3 additive is employed to dope perovskite layer. The dual-additive strategy is used to optimize the microstructure and regulate the optoelectrical characteristics of carbon-based CsPbIBr2 PSCs. It is found that CsAc can passivate the vacancy defect of Br−, reduce the energy loss (Eloss) and enhance the open-circuit voltage (Voc) of PSCs. The HPbI3 additive works to optimize the crystallization process, resulting in the high-quality CsPbIBr2 films with better crystallinity and morphology. The modified films by CsAc and HPbI3 dual-additive demonstrate smaller band gap, better light absorption, reduced trap-state density (Ntrap) and suppressed carrier recombination. The optimized carbon-based PSCs modified by the dual-additive achieve a champion power conversion efficiency of 9.18% with a Voc of 1.334 V, more matched energy-level, reduced Eloss and promoted charge transfer. Moreover, the modified PSCs without encapsulation show improved long-term humid stability. Our work provides a facilitated method to prepare an efficient and stable CsPbIBr2 PSCs by low-temperature process.

Suppressing Phase Segregation in CsPbIBr2 Films via Anchoring Halide Ions toward Underwater Solar Cells

Inorganic CsPbIBr2 perovskite solar cells (PSCs) have accomplished many milestones, yet their progress has been constrained by ion migration and phase separation. This study explores the modulation of perovskite crystallization kinetics and halide ion migration through chlorobenzene (CB) antisolvent with bis(pentafluorophenyl)zinc (Zn(C6F5)2) additive. The photoluminescence and absorption spectra reveal the significantly reduced phase segregaton in CsPbIBr2 film treated by CB with Zn(C6F5)2. Moreover, this research analyzes the CsPbIBr2 film's free carrier lifetime, diffusion length, and mobility using time-resolved microwave conductivity and transient absorption spectroscopy after Zn(C6F5)2 modification. Consequently, the modified CsPbIBr2 PSCs offer a 12.57% power conversion efficiency (PCE), the highest value among CsPbIBr2 PSCs with negligible hysteresis and prolonged stability. Furthermore, under 1-m-deep water, CsPbIBr2 PSCs display a PCE of 14.18%. These findings provide an understanding of the development of phase-segregation-free CsPbIBr2 films and showcase the prospective applications of CsPbIBr2 PSCs in underwater power systems.

Efficient inorganic perovskite solar cells made by drop-coating in ambient air

Inorganic perovskites are receiving growing attention due to good thermal stability and fast-improving photovoltaic performance. However, most of the high-efficiency inorganic perovskite solar cells (PSCs) were fabricated in inert atmosphere. Herein, we report an additive-assisted airflow drying (AAD) method to make mixed-halide inorganic perovskite films in ambient air. The nucleation and crystal growth during film formation are controlled by using airflow dying and lead acetate trihydrate additive, producing pinhole-free film with low defect density. Consequently, efficiency of CsPbI2.25Br0.75 PSCs is improved to 18.49%, which is the highest for wide-bandgap (>1.8 eV) inorganic PSCs. An efficiency of 17.08% is achieved for PSCs made under moderate relative humidity (40–50%). Moreover, PCEs of 17.39% and 11.54% are achieved for CsPbI2Br and CsPbIBr2 PSCs, respectively, which are among the best PCEs for CsPbI2Br and CsPbIBr2 PSCs. This work provides a convenient and efficient method to make efficient inorganic PSCs in ambient air.

Effect of Li-doped TiO2 layer on the photoelectric performance of carbon-based CsPbIBr2 perovskite solar cell

Carbon-based CsPbIBr2 perovskite solar cells (PSCs) have attracted much attention due to their excellent photoelectric properties and low cost fabrication processes. The TiO2 has been diffusely employed as electron-transporting layer (ETL) for carbon-based CsPbIBr2 PSC. However, the lower electron mobility for TiO2 restricts the performance improvement. The tactics of ion doping is normally used to improve the ETL performance. In this study, Li-doped TiO2 (Li: TiO2) is used as a novel ETL for carbon-based planar CsPbIBr2 PSC. There is no change in the optical band gap of TiO2 after the incorporation of Li. However, Li-doping can effectively improve the crystallinity of TiO2 film and reduce the dark current and charge recombination of CsPbIBr2 PSC. Comparing with the TiO2-based CsPbIBr2 PSC, the efficiency of CsPbIBr2 PSC with the Li: TiO2 ETL increases from 6.63% to 8.09%. Additionally, the use of the Li: TiO2 ETL also has a positive impact on the long-term stability of the CsPbIBr2 PSC. This work indicates that ion doping can offer a new route to produce effective ETL for the development of highly-efficient CsPbIBr2 solar cell with a interface engineering concept.

Double-side modification strategy for efficient carbon-based, all-inorganic CsPbIBr2 perovskite solar cells with high photovoltage

CsPbIBr2 has attracted great attention due to its balanced bandgap and stability features. However, one-step prepared CsPbIBr2 films are generally of poor quality, hindering the performance improvement of the resulting perovskite solar cells (PSCs). Herein, we report the fabrication of high-performance carbon-based, all-inorganic CsPbIBr2 PSCs with a double-side modification strategy using PEAI/PEABr. We tune the crystallization behavior and passivate the defects of CsPbIBr2 films with modifications of their bottom and top surfaces with PEAI and PEABr, respectively. This causes the PEA cation to form a double layer of armor on both sides of the CsPbIBr2 precursor film and can provide the anions of the required I and Br. The collaborative strategy of crystallization and defect passivation for CsPbIBr2 films is exceptionally effective. It produces a fully covered CsPbIBr2 film with an average grain size increase of more than 50%, few grain boundaries, and high crystallinity. Moreover, this strategy also suppresses pinhole formation, reduces the charge trap density, and prolongs the carrier recombination lifetime. Hence, carbon-based all-inorganic PSCs with the desired CsPbIBr2 films yield an optimized efficiency of 9.96% with a particularly high photovoltage of 1.32 V. Our work provides guidance for simultaneous crystallization control and defect passivation to further improve the performance of PSCs.

Nano Ag-enhanced photoelectric conversion efficiency in all-inorganic, hole-transporting-layer-free CsPbIBr2 perovskite solar cells

All-inorganic, hole-transporting-layer-free CsPbIBr2 perovskite solar cells have great potential for development, but their device performance needs to be further improved. Recently, metal nanostructures have been successfully applied in the field of solar cells to improve their performance. Nano Ag-enhanced power conversion efficiency (PCE) in one CsPbIBr2 perovskite solar cell utilizing localized surface plasmons of Ag nanoparticles (NPs) on the surface has been researched experimentally and by simulation in this paper. The localized surface plasmon resonance of Ag NPs has a near-field enhancement effect, which is expected to improve the light absorption of CsPbIBr2 perovskite photovoltaic devices. In addition, Ag NPs have a forward-scattering effect on the incident light, which can also improve the performance of CsPbIBr2-based perovskite photovoltaic devices. By directly assembling Ag NPs (with a size of about 150 nm) on the surface of fluorine-doped tin oxide it is found when the particle surface coverage is 10%, the CsPbIBr2 perovskite photovoltaic device achieves a best PCE of 2.7%, which is 9.76% higher than that of the control group. Without changing any existing structure in the ready-made solar cell, this facile and efficient method has huge applications. To the best of our knowledge, this paper is the first report on nano Ag-enhanced photoelectric conversion efficiency in this kind of CsPbIBr2 perovskite solar cell.

Surface passivation and hole extraction: Bifunctional interfacial engineering toward high-performance all-inorganic CsPbIBr2 perovskite solar cells with efficiency exceeding 12%

All-inorganic CsPbIBr2 perovskite solar cells (PSCs) have attracted considerable research attention in recent years due to their excellent thermal stability. However, their power conversion efficiencies (PCEs) are relatively low and still far below the theoretical limit. Here, we report the use of an organic dye molecule (namely VG1-C8) as a bifunctional interlayer between perovskite and the hole-transport layer in CsPbIBr2 PSCs. Combined experimental and theoretical calculation results disclose that the multiple Lewis base sites in VG1-C8 can effectively passivate the trap states on the perovskite films. Meanwhile, the π-conjugated dye molecule significantly accelerates the hole extraction from the perovskite absorber as evidenced by the photoluminescence analysis. Consequently, the VG1-C8 treatment simultaneously boosts the photovoltage and photocurrent density values from 1.26 V and 10.80 mA cm−2 to 1.31 V and 12.44 mA cm−2, respectively. This leads to a significant enhancement of PCE from 9.20% to 12.10% under one sun irradiation (AM 1.5G). To our knowledge, this is the record efficiency reported so far for CsPbIBr2 PSCs. Thus, the present work demonstrates an effective interfacial passivation strategy for the development of highly efficient PSCs.

Improvement of green antisolvent-isopropanol and additive-thiourea on carbon based CsPbIBr2 perovskite solar cells

In recent years, all-inorganic perovskite cells (PSCs) have been widely studied by researchers because of their excellent thermal and optical stability. Among them, the CsPbIBr2 PSCs with carbon electrode have attracted extensive attention because of its excellent stability, low preparation difficulty, easy commercialization and low cost. However, the crystal quality of CsPbIBr2 film is poor. There are a large number of pinholes and surface defects (Pb2+ exposure), which will lead to internal short circuit and a large number of nonradiative recombination, thus affecting the photoelectric conversion efficiency (PCE). Although these problems can be improved by antisolvent engineering, the traditional antisolvent chlorobenzene (CB) and toluene (TL) are highly toxic and harmful to the environment. In this paper, isopropanol (IPA) is used as a green antisolvent to improve the quality of CsPbIBr2 films, and S2− with strong reducibility and passivation defects are successfully introduced into the CsPbIBr2 film surface by further adding thiourea as Lewis base to IPA (IPA-S). After the CsPbIBr2 films were treatment by IPA-S antisolvent, we successfully obtained high-quality CsPbIBr2 films with large grain size and no pinholes. Moreover, through XPS, PL, EIS and other tests, it is found that the S2− introduced by IPA-S can combine with the exposed Pb2+ on the CsPbIBr2 surface to passivate the defects, it is beneficial to reduce the non-radiative recombination and improve the transport capacity of carriers. Finally, the results of this paper prove that that the champion PCE of carbon based CsPbIBr2 PSCs treated with IPA-S antisolvent was 6.79%, which was nearly 30% higher than the original carbon based CsPbIBr2 PSCs. In addition, due to the strong reducibility of S2−, the carbon based CsPbIBr2 PSCs treated with isopropanol antisolvent added with thiourea can continue to work in air with 40% relative humidity, and the efficiency can remain 85% within 10 days. In order to improve the performance and stability of the all-inorganic PSCs, this paper provides a non-toxic, environmentally friendly and effective scheme.

Double‐Side Interface Engineering Synergistically Boosts the Efficiency of Inorganic CsPbIBr2 Perovskite Solar Cells Over 12%

AbstractAll‐inorganic CsPbIBr2 perovskite solar cells (PSCs) have aroused the worldwide interest because of their excellent thermal stability. However, the bottom and upper surfaces of CsPbIBr2 films are vulnerable to surface defects, corroding the carrier dynamic in PSCs. Meanwhile, the band alignment mismatch also affects the interfacial carrier transport. Therefore, this work systematically investigates the passivation effect and band alignment of rubidium acetate (RbAc) interface layer at electron transport layer (ETL)/perovskite and perovskite/hole transport layer (HTL), respectively. When RbAc is introduced to ETL/perovskite interface, the improved morphology quality of CsPbIBr2 films and the elevated conductive band minimum of SnO2 leads to effective electron extraction and band alignment. Furthermore, once RbAc is introduced to perovskite/HTL interface, it passivates grain boundary defects and reduces the roughness of CsPbIBr2 films, contributing to reduced nonradiative recombination. In addition, the raised valence band maximum of CsPbIBr2 also accelerates the hole transfer. It is found that each single‐side interface modification contributes to improved photovoltaic performance and air stability. Consequently, a synergy effect of double‐side interface modification is investigated for improving the device efficiency. Accordingly, the modified PSCs achieve a champion efficiency of 12.11%, which is increased by 30.78% compared to that of the pristine devices.

Van der Waals Epitaxial Growth for High Performance Organic‐Free Perovskite Solar Cell: Experimental and Theoretical Insights

AbstractAll‐inorganic perovskite solar cells (PSCs) are most promising in yielding stabilized power conversion efficiencies (PCE) as compared to their hybrid organic–inorganic counterparts. However, all‐inorganic PSCs have suffered from low efficiency due to significant charge carrier recombination within perovskite active layer (PAL) bulk and at the carrier selective interfaces (CSI). Boosting the PCE through the remedy to both issues seems to be the only Achilles‐Heal on their way to commercialization. Here, a synergistic approach of liquid‐exfoliated molybdenum disulfide (MoS2) at the PAL (CsPbIBr2)/hole transport layer (NiO) interface to enhance the perovskite grain growth and stabilize the hole transport layer (HTL)/PAL interface against the carrier recombination within the PAL bulk and at the interface is reported. The in‐plane coupling between MoS2 crystal lattice and CsPbIBr2 is strongly revealed through transmission electron microscopy (TEM) results, which favored the van der Waals epitaxial growth of CsPbIBr2 PAL toward the larger crystalline grain sizes, preferential growth along (110), i.e., normal to MoS2, and low trap‐density. Therefore, the PCE of organic‐free CsPbIBr2 PSC is increased to as high as 10.98% under 1‐sun illumination, which is 48% higher than the pristine device (7.38%), which concludes that this strategy can be integrated to other analogous perovskite compositions.

Bifunctional Passivation for Efficient and Stable Low-Temperature Processed All-Inorganic CsPbIBr2 Perovskite Solar Cells

Carbon-based all-inorganic CsPbIBr 2 perovskite solar cells (PSCs) have attracted a lot of attention due to their simple fabrication process and good thermal stability. But the efficiency of devices is lower due to the poor quality of the solution-processed CsPbIBr 2 film. A high-quality CsPbIBr 2 film with large grain size , good crystallinity and reduced trap-state density is necessary for efficient PSCs. In this work, fluorine-containing trifluoroethyl methacrylate (TFEMA) is employed to improve the microstructure and photoelectrical properties of the low-temperature processed CsPbIBr 2 film. Our all-inorganic PSCs consist of the FTO/TiO 2 /CsPbIBr 2 /carbon simple structure. The power conversion efficiency (PCE) of the modified PSCs using TFEMA (TFEMA-PSCs, 8.54%) is much higher than 31.8% of the Reference-PSCs (6.48%) and an open-circuit voltage (V oc ) of 1.305 V was achieved. The reasons for the improved performance have been systematically investigated. The characterizations show that the enhanced PCE in the TFEMA-PSCs can be ascribed to the optimized microstructure, decreased carrier recombination, reduced trap-state density and promoted charge transfer. This work provides an effective and facile strategy to prepare high-quality CsPbIBr 2 films by low-temperature process.

Multidimensional Function Upgradation of All‐Inorganic CsPbIBr2 Perovskite Film by Doping an Ionic Additive for Carbon–Electrode‐Based Solar Cells

All‐inorganic CsPbIBr2 perovskite solar cells (PSCs) recently demonstrated great superiority for application in tandem and semitransparent photovoltaics because of their excellent phase stability. However, compared to state‐of‐the‐art PSCs, the inferior film quality is harmful for the photovoltaic performance improvement. Herein, a novel ionic additive, tetrabutylammonium hexafluorophosphate (TBAPF6), is employed to improve the all‐inorganic CsPbIBr2 perovskite film quality and passivate detrimental defects. By assembly into carbon–electrode‐based solar cells, a champion efficiency as high as 10.57% is achieved, which is much higher than that of a control device with 8.30% efficiency, mainly attributed to the suppressed non‐radiative recombination. More importantly, the presence of alkyl chains and fluorine atoms in TBAPF6 significantly increases the hydrophobicity of perovskite films and therefore improves the long‐term stability under harsh conditions without encapsulation.