Long-term Stable Perovskite Solar Cells Research Articles

Long-term stable perovskite solar cells prepared by doctor blade coating technology using bilayer structure and non-toxic solvent

The doctor blade coating technology for the perovskite solar cells (PSCs) is studied. The bilayer and triple-layer structures based on CsFAPb(IBr)3 and MAPbI3 layers were designed and fabricated by the doctor blade coating. The conventional highly toxic dimethylformamide (DMF) used in the precursors are replaced by the mixtures of gamma-butyrolactone (GBL) and dimethyl sulfoxide (DMSO). Single cation and mixed-cation perovskite layer with different stacks are also compared. It is found that the as-prepared single cation perovskite (MAPbI3) PSCs have better photovoltaic performance but worse lifetime than those of the mixed-cation perovskite (CsFAPb(IBr)3) PSCs. Additionally, the bi-layer structure PSC has a brighter and smoother surface, higher quantum efficiency, and higher crystallinity. Those factors concerning the MAPbI3/CsFAPb(IBr)3(upper/lower) solar cell to have superior properties and better lifetime under the elevated temperature and humidity than that of the CsFAPb(IBr)3/MAPbI3(upper/lower) solar cell. Moreover, when the MAPbI3 is used as the capping layer of the CsFAPb(IBr)3/MAPbI3 bilayer PCS, its photovoltaic performance is better. Secondary ion mass spectroscopy indicates that MAPbI3 capping layer has better ability to dissolve the bottom layers than that of CsFAPb(IBr)3 due to the reduction of inter-diffusion of molecules and smooth surface during lifetime test. Finally, the MAPbI3/CsFAPb(IBr)3 bilayer device shows the best initial power conversion efficiency (PCE), Voc, and Jsc of 15.4%, 1.01 V, and 20.7 mA/cm2 respectively. The encapsulated PSC keeps 92% of original PCE under ambient environment at room temperature and relative humidity of 40% after 1000 h.

Multiple bonding effects of 1-methanesulfonyl-piperazine on the two-step processed perovskite towards efficient and stable solar cells

Interfacial engineering is a highly effective strategy to improve device performance of perovskite solar cells (PSCs) by alleviating the defect-induced non-radiative recombination, while reports on defect passivation of the two-step processed perovskite films are quite limited to date. Herein, a new type of multifunctional molecule, 1-methanesulfonyl-piperazine (MP), is applied to modify the perovskite film that is fabricated via a two-step process. The introduction of MP passivation enables multiple bonding interactions with perovskite film, i.e., hydrogen bond, Pb-O and Pb-N dative bonds, resulting in significantly reduced trap density and effectively suppressed non-radiative recombination. Moreover, the MP-modified perovskite films show improved crystallinity with decreased PbI2 residuals, which is conducive to both carrier transport and stability of the resultant devices. As a consequence, the MP-modified devices present an impressive power conversion efficiency (PCE) of 23.4% along with enhanced stability, e.g., the unencapsulated device retains 88% of its original PCE even subject to thermal aging at 85 ℃ for 600 h. This work opens up an avenue to explore functional materials for high-performance and long-term stable PSCs.

Revealing phase evolution mechanism for stabilizing formamidinium-based lead halide perovskites by a key intermediate phase

Revealing phase evolution mechanism for stabilizing formamidinium-based lead halide perovskites by a key intermediate phase

Hydrophobic compressed carbon/graphite based long-term stable perovskite solar cells

Carbon/graphite nanocomposite (CGn) film had been employed as cathode for hole transport layer (HTL) free, mesoscopic, heterojunction perovskite solar cells (PSCs). Hydrophobic CGn film shows impressive charge transport characteristics that makes it promising candidate for cathode in HTL free PSCs. The electrochemical impedance spectroscopy measurements realised the significant charge transport characteristics can get for (10 μm–14 μm) thin film. On the other hand, the hydrophobic (Contact Angle 126°) CGn film after compression by 160 kPa pressure, become nearly superhydrophobic (Contact Angle 140°) greatly improve the conductivity of electrode 3x fold from 0.75 S/cm to 2.25 S/cm and subsequently, photovoltaic performance enhancement by 56% in efficiency and 80% in Jsc from its performance without compression and enhanced stability to a greater extent. A thin 20 nm Alumina had been used as an electron blocker to inhibit electron transfer into carbon and avoid recombination that enhanced the efficiency and charge collection (Jsc) by 30%, 64% respectively from its photovoltaic parameter without alumina. Moreover, CGn counter electrode-based PSCs extends stability remarkably in ambient atmospheric condition more than 7000 h.

A critical review of materials innovation and interface stabilization for efficient and stable perovskite photovoltaics

Perovskite solar cells (PSCs) based on organometal halide (Omh) perovskites have been exhibited superb potential for next-generation photovoltaic applications because of their ever-increasing power conversion efficiencies over the past decade. However, their operational stability remains a challenge, which are attributed to the ionic nature of Omh perovskites and defects of heterojunction interfaces in a stacked solar cell. Thus, stabilization of Omh perovskites phases and device interfaces are of paramount importance towards long-term stable PSCs. This review presents an important tool to explore efficient and stable PSCs by Omh perovskite-based composites and interface stabilization strategies. Moreover, it deals with the study on materials selection for effective design of Omh perovskite composites and cell heterojunction interfaces. The chemical and electrical characteristics of Omh perovskite composites and device interface states, including perovskite film growth, defect tolerance, interface trap passivation, strong chemical interaction, cross-linking and/or chemical bonding, are further discussed. These features provide insights into the stabilization and immobilization of Omh perovskite structures and stacked solar cell interfaces for highly efficient and stable perovskite photovoltaics. Recent progress in materials innovation and interface stabilization for highly efficient and operationally-stable perovskite photovoltaics. • Degradation factors and their mechanisms in perovskite photovoltaics are briefly analyzed. • Judicious strategies to stabilize perovskites phases and solar cell heterojunction interfaces are reviewed. • Key works related to efficient perovskite photovoltaics by materials innovation and interface stabilization are presented.

Mechanistic Understanding of Cetyltrimethylammonium Bromide-Assisted Durable CH3NH3PbI3 Film for Stable ZnO-Based Perovskite Solar Cells

Long-term stable perovskite solar cells (PSCs) fabricated in ambient conditions are highly desirable. However, the stable perovskite film has yet to be easily controlled in open air, especially emp...

Magnetron sputtered all-metal-oxide layers with balanced charge carrier transport efficiency for long-term stable perovskite solar cells

Despite the great advance in power conversion efficiency (PCE), the poor stability of perovskite solar cells in ambient condition becomes a tremendous obstruction for real application. Solution-processed all-metal-oxide charge transport layers exhibit remarkable improvement in stability in ambient air according to the previous report. However, the solution process is confined to the limited effective area and morphology of the substrate. Here we report the magnetron sputtered charge transport layers, of which Cu doped NiOx (Cu:NiOx) acts as the hole transport layer and ZnO as the electron transport layer, respectively. We precisely control their properties on unlimited substrates without post-annealing for balanced charge transport efficiency in both interfaces, which demonstrates better power conversion efficiency. The all-metal-oxide based devices also demonstrate excellent stability in ambient condition when compared to the control devices based on conventional organic transport layers.

The role of carbon-based materials in enhancing the stability of perovskite solar cells

Enhancing the stability of perovskite solar cells is crucial to the deployment of this technology. Carbon-based materials are promising candidates for providing long-term stable perovskite solar cells suitable for commercialization.

Enhanced stability and performance of air-processed perovskite solar cells via defect passivation with a thiazole-bridged diketopyrrolopyrrole-based π-conjugated polymer

Efficient (power conversion efficiency up to 20.30%) and long-term stable perovskite solar cells are demonstrated by inserting a semiconducting polymer PTzDPPBTz as the passivation layer.

Inorganic CuFeO2 Delafossite Nanoparticles as Effective Hole Transport Materials for Highly Efficient and Long-Term Stable Perovskite Solar Cells.

The regular architecture (n-i-p) of perovskite solar cells (PSCs) has attracted increasing interest in the renewable energy field, owing to high certified efficiencies in the recent years. However, there are still serious obstacles of PSCs associated with spiro-OMeTAD hole transport material (HTM), such as (i) prohibitively expensive material cost (∼150-500 $/g) and (ii) operational instability at elevated temperatures and high humidity levels. Herein, we have reported the highly photo, thermal, and moisture-stable and cost-effective PSCs employing inorganic CuFeO2 delafossite nanoparticles as a HTM layer, for the first time. By exhibiting superior hole mobility and additive-free nature, the best-performing cell achieved a power conversion efficiency (PCE) of 15.6% with a negligible hysteresis. Despite exhibiting a lower PCE as compared to the spiro-OMeTAD-based control cell (19.1%), nonencapsulated CuFeO2-based cells maintained above 85% of their initial efficiency, while the PCE of control cells dropped to ∼10% under continuous illumination at maximum power point tracking after 1000 h. More importantly, the performance of control cells was quickly degraded at above 70 °C, whereas CuFeO2-based cells, retaining ∼80% of their initial efficiency after 200 h, were highly stable even at 85 °C in ambient air under dark conditions. Besides showing significant improvement in stability against light soaking and thermal stress, CuFeO2-based cells exhibited superior shelf stability even at 80 ± 5% relative humidity and retained over 90% of their initial PCE. Overall, we strongly believe that this study highlights the potential of inorganic HTMs for the commercial deployment of long-term stable and low-cost PSCs.

Phenothiazine Functionalized Multifunctional A-π-D-π-D-π-A-Type Hole-Transporting Materials via Sequential C-H Arylation Approach for Efficient and Stable Perovskite Solar Cells.

Three phenothiazine-based A-π-D-π-D-π-A-type small molecules containing various terminal acceptor units, which act as Lewis base blocks, have been synthesized via an efficient and step-economical, direct C-H arylation strategy in the aim toward the development of hole-transporting materials (HTMs) with multifunctional features (such as efficient hole extraction layer, trap passivation layer, and hydrophobic protective layer) for perovskite solar cells (PrSCs). Optical-electrochemical correlation and density functional theory studies reveal that dicyanovinylene acceptor in SGT-421 downshifted the highest occupied molecular orbital (HOMO) level (-5.41 eV), which is more proximal to the valence band (-5.43 eV) of the perovskite, whereas N-methyl rhodanine in SGT-420 and 1,3-indanedione (IND) in SGT-422 destabilized the HOMO, leading to an increased interfacial energy-level offset. SGT-421 exhibits superior properties in terms of a sufficiently low-lying HOMO level and favorable energy-level alignment, intrinsic hole mobility, interfacial hole transfer, hydrophobicity, and trap passivation ability over spiro-OMeTAD as a benchmark small-molecule HTM. As envisaged in the design concept, SGT-421-based PrSC not only yields a comparable efficiency of 17.3% to the state-of-art of spiro-OMeTAD (18%), but also demonstrates the enhanced long-term stability compared to the spiro-OMeTAD because of its multifunctional features. More importantly, the synthetic cost of SGT-421 is estimated to be 2.15 times lower than that of spiro-OMeTAD. The proposed design strategy and the study of acceptor-property relationship of HTMs would provide valuable insights into and guidelines for the development of new low-cost and efficient multifunctional HTMstowardthe realization of efficient and long-term stable PrSCs.

Long-term stable perovskite solar cells with room temperature processed metal oxide carrier transporters

A hydrophobic electron transporter is introduced to enhance the moisture stability of perovskite solar cells (PSCs). The calcine-free deposition of carrier transporters contributes to achieving stable, scalable and reproducible PSCs with low cost.

The Impact of Nano- and Microstructure on the Stability of Perovskite Solar Cells.

Halide perovskites have emerged recently as a promising candidate for the next generation of photovoltaics. Power conversion efficiencies for laboratory-scale devices surpass those of established technologies, such as multicrystalline silicon. However, perovskite solar cells lose their initial efficiency rapidly due to the convolution of several degradation factors, which hinder the process of industrialization. In this review, the important role of the nano- and microstructure of the perovskite layer in the performance and stability of the device are discussed. The defects located predominantly at the grain boundaries within the perovskite film and at the interface of the perovskite with the other materials can compromise the devices' stability. Thus, lowering the surface and interface concentration of defects is a key approach toward long-term stable perovskite solar cells.

Covalently Connecting Crystal Grains with Polyvinylammonium Carbochain Backbone To Suppress Grain Boundaries for Long-Term Stable Perovskite Solar Cells.

Grain boundaries act as rapid pathways for nonradiative carrier recombination, anion migration, and water corrosion, leading to low efficiency and poor stability of organometal halide perovskite solar cells (PSCs). In this work, the strategy suppressing the crystal grain boundaries is applied to improve the photovoltaic performance, especially moisture-resistant stability, with polyvinylammonium carbochain backbone covalently connecting the perovskite crystal grains. This cationic polyelectrolyte additive serves as nucleation sites and template for crystal growth of MAPbI3 and afterward the immobilized adjacent crystal grains grow into the continuous compact, pinhole-free perovskite layer. As a result, the unsealed PSC devices, which are fabricated under low-temperature fabrication protocol with a proper content of polymer additive PVAm·HI, currently exhibit the maximum efficiency of 16.3%. Remarkably, these unsealed devices follow an "outside-in" corrosion mechanism and respectively retain 92% and 80% of the initial PCE value after being exposed under ambient environment for 50 days and 100 days, indicating the superiority of carbochain polymer additives in solving the long-term stability problem of PSCs.

(Invited) Inorganic Charge Transport Materials Grown By Atomic Layer Deposition for Highly Efficient and Long-Term Stable Perovskite Solar Cells

Lead halide perovskite solar cells have recently attracted huge attention because of their dramatic rise in power conversion efficiency (PCEs) within few years. However, high PCEs have not been thoroughly guaranteed for long-term period of test under continuous illumination. Here, we report highly efficient perovskite solar cells having a long-term stability that adapts uniform and dense inorganic charge transport layer (NiO and Ti-S compounds) grown by atomic layer deposition (ALD) at relatively lower temperature. Ultra-thin un-doped NiO films, with much less absorption loss, were prepared by ALD with a highly precise control over the thickness. Thin enough (5 ~ 7.5 nm in thickness) NiO films with the thickness of few times of Debye length ( 1 ~ 2 nm for NiO) show enough conductivities achieved by overlapping space charge regions, which finally exhibited a highest PCE of 16.40 % with high open circuit voltage of 1.04 V and fill factor of 0.72 with a negligible current-voltage hysteresis. Furthermore, highly dense inorganic electron transport layer has been directly deposited onto perovskite using non-aqueous ALD process at room temperature, which ensures no degradation of perovskite. This inorganic layer demonstrated efficient electron transporting as well as highly passivating performance. Finally, perovskite solar cells that using inorganic charge transport layers with large area (> 10 cm2) were fabricated and their long-term stability under light soaking were characterized.

Not All That Glitters Is Gold: Metal-Migration-Induced Degradation in Perovskite Solar Cells.

Perovskite solar cells (PSCs) have now achieved efficiencies in excess of 22%, but very little is known about their long-term stability under thermal stress. So far, stability reports have hinted at the importance of substituting the organic components, but little attention has been given to the metal contact. We investigated the stability of state-of-the-art PSCs with efficiencies exceeding 20%. Remarkably, we found that exposing PSCs to a temperature of 70 °C is enough to induce gold migration through the hole-transporting layer (HTL), spiro-MeOTAD, and into the perovskite material, which in turn severely affects the device performance metrics under working conditions. Importantly, we found that the main cause of irreversible degradation is not due to decomposition of the organic and hybrid perovskite layers. By introducing a Cr metal interlayer between the HTL and gold electrode, high-temperature-induced irreversible long-term losses are avoided. This key finding is essential in the quest for achieving high efficiency, long-term stable PSCs which, in order to be commercially viable, need to withstand hard thermal stress tests.

Achieving long-term stable perovskite solar cells via ion neutralization

Corrosive ionic defects in perovskite films degrade perovskite solar cells (PSCs) and long-term stable PSCs are realized by neutralizing the defects.