Tin halide perovskites attract incremental attention to deliver lead‐free perovskite solar cells. Nevertheless, disordered crystal growth and low defect formation energy, related to Sn(II) oxidation ...to Sn(IV), limit the efficiency and stability of solar cells. Engineering the processing from perovskite precursor solution preparation to film crystallization is crucial to tackle these issues and enable the full photovoltaic potential of tin halide perovskites. Herein, the ionic liquid n‐butylammonium acetate (BAAc) is used to tune the tin coordination with specific O…Sn chelating bonds and NH…X hydrogen bonds. The coordination between BAAc and tin enables modulation of the crystallization of the perovskite in a thin film. The resulting BAAc‐containing perovskite films are more compact and have a preferential crystal orientation. Moreover, a lower amount of Sn(IV) and related chemical defects are found for the BAAc‐containing perovskites. Tin halide perovskite solar cells processed with BAAc show a power conversion efficiency of over 10%. This value is retained after storing the devices for over 1000 h in nitrogen. This work paves the way toward a more controlled tin‐based perovskite crystallization for stable and efficient lead‐free perovskite photovoltaics.
The synergistic strategy of tuning the solution coordination and crystallization process by introducing ionic liquid is implemented to successfully fabricate pinhole‐free tin perovskite films with preferential crystal orientation, which possess improved oxidation repellency for Sn(II) and enhanced hydrophobicity. As a result, the stabilization of high‐efficiency lead‐free tin halide perovskite solar cells is achieved.
While perovskite solar cells have skyrocketed in recent years to power conversion efficiencies competitive with those of silicon and thin-film photovoltaics, the lagging behind stability stands in ...the way of commercialisation. In this review, we discuss the reasons and factors that induce the degradation in photovoltaic performance of perovskite solar cells, and furthermore, we summarise the most promising strategies to enhance the lifespan. We show that each component of the device, including the charge selective contacts, perovskite layer, and electrodes, can be engineered to reduce the influence of heat, UV light, oxygen, moisture and their synergetic effect on the operating lifetime of devices. We conclude that inorganic contacts and inorganic perovskite compositions are the most promising direction toward stable perovskite solar cells.
All inorganic perovskite solar cells lead to extended device lifespan in an accelerated ageing test.
The power conversion efficiency (PCE) of NiO based perovskite solar cells has recently hit a record 22.1% with a hybrid organic-inorganic perovskite composition and a PCE above 15% in a fully ...inorganic configuration was achieved. Moreover, NiO processing is a mature technology, with different industrially attractive processes demonstrated in the last few years. These considerations, along with the excellent stabilities reported, clearly point towards NiO as the most efficient inorganic hole selective layer for lead halide perovskite photovoltaics, which is the topic of this review. NiO optoelectronics is discussed by analysing the different doping mechanisms, with a focus on the case of alkaline and transition metal cation dopants. Doping allows tuning the conductivity and the energy levels of NiO, improving the overall performance and adapting the material to a variety of perovskite compositions. Furthermore, we summarise the main investigations on the NiO/perovskite interface stability. In fact, the surface of NiO is commonly oxidised and reactive with perovskite, also under the effect of light, thermal and electrical stress. Interface engineering strategies should be considered aiming at long term stability and the highest efficiency. Finally, we present the main achievements in flexible, fully printed and lead-free perovskite photovoltaics which employ NiO as a layer and provide our perspective to accelerate the improvement of these technologies. Overall, we show that adequately doped and passivated NiO might be an ideal hole selective layer in every possible application of perovskite solar cells.
The power conversion efficiency of NiO based perovskite solar cells has recently hit a record 22.1%. Here, the main advances are reviewed and the role of NiO in the next breakthroughs is discussed.
In perovskite solar cells (PSCs), the interfaces are a weak link with respect to degradation. Electrochemical reactivity of the perovskite's halides has been reported for both molecular and polymeric ...hole selective layers (HSLs), and here it is shown that also NiO brings about this decomposition mechanism. Employing NiO as an HSL in p–i–n PSCs with power conversion efficiency (PCE) of 16.8%, noncapacitive hysteresis is found in the dark, which is attributable to the bias‐induced degradation of perovskite/NiO interface. The possibility of electrochemically decoupling NiO from the perovskite via the introduction of a buffer layer is explored. Employing a hybrid magnesium‐organic interlayer, the noncapacitive hysteresis is entirely suppressed and the device's electrical stability is improved. At the same time, the PCE is improved up to 18% thanks to reduced interfacial charge recombination, which enables more efficient hole collection resulting in higher Voc and FF.
Hysteresis in the dark, attributable to bias induced degradation of the p‐type interface, is investigated and eliminated in NiO‐based inverted perovskite solar cells. Enhanced stability to forward bias is obtained with the introduction of a low‐temperature hybrid magnesium‐based interlayer.
Abstract
Due to their outstanding optoelectronic properties, lead-based halide perovskite materials have been applied as efficient photoactive materials in solution-processed solar cells. Current ...record efficiencies offer the promise to surpass those of silicon solar cells. However, uncertainty about the potential toxicity of lead-based halide perovskite materials and their facile dissolution in water requires a search for new alternative perovskite-like materials. Thanks to the foresight of scientists and their experience in lead-based halide perovskite preparation, remarkable results have been obtained in a short period of time using lead-free perovskite compositions. However, the lower solar-to-energy conversion efficiency and long-term stability issues are serious drawbacks that hinder the potential progression of these materials. Here, we review and analyse strategies in the literature and the most promising solutions to identify the factors that limit the power conversion efficiency and long-term stability of lead-free tin-based perovskite solar cells. In the light of the current state-of-the-art, we offer perspectives for further developing these promising materials.
Poly (triaryl amine) (PTAA) is one of the promising hole transport materials (HTM) for perovskite solar cells. Highly efficient PTAA-devices have been demonstrated in both direct (n-i-p) and inverted ...(p-i-n) architectures. In the inverted structures, the device suffers from poor coverage of the perovskite film over the hydrophobic PTAA surface. To address this issue, we exploited an easy and efficient approach utilizing a short-time UV treatment of the PTAA layer prior to the perovskite deposition. The UV-treatment improved the optical properties of PTAA layers, which synergistically helps the light harvesting of the perovskite. Enhanced grain sizes, together with the decrease of recombination centers in the UV treated dopant-free PTAA, lead to efficient perovskite solar cell with PCE reaching 19.17% for 0.09 cm2 active area. Moreover, the device retains over 75% of its initial efficiency after 1400 h storage in ambient condition with average relative humidity (RH) of 50%. Additionally, the effect of UV light was studied on PTAA with different molecular weights. Non-destructive UV exposure more predominantly improved the efficiency of lower molecular weight PTAA-based device. A maximum PCE of 12.3% for 1 cm2-sized cells using 5 min-UV PTAA with low MW is achieved.
This investigation points to the main roles of the HTL quality for the development of high-efficiency photovoltaic solar cells and provides a fast, easy and cost-effective method toward upscaling.
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•A high quality perovskite film based on PTAA hole transport layer was fabricated.•Uniform hydrophilicity of PTAA was carried out by its UV treatment.•An improvement in performance and stability was observed by the UV treatment.•Effect of UV treatment on PTAA layers with different molecular weights was studied.
Electrodeposition of NiOOH is an attracting route toward nanosized films of NiO, a p-type semiconductor used in many advanced applications. In this paper, the deposition mechanism is thoroughly ...investigated aiming at the clarification of the deposition dynamics and the chemical nature of the deposit. We focused on initial stages of the potentiostatic deposition on ITO, which yields a nanostructured film. In the potential range investigated the process is mass transport controlled and strongly overlaps with oxygen evolution reaction. The nucleation regime, which is finely tunable, correlates with the surface extension of the film. Supporting electrolytes are found to suppress the deposition, likely by modifying the nickel speciation in the aqueous electrolyte. Further, through XPS investigation we shed light on the mixed γ−β NiOOH nature of the deposited film and its electrochemistry. This work provides precious understanding for future exploitations of anodic electrodeposited NiO, especially in applications where a strict control on surface morphology and thickness at the nanoscale level is mandatory.
The operation of halide perovskite optoelectronic devices, including solar cells and LEDs, is strongly influenced by the mobility of ions comprising the crystal structure. This peculiarity is ...particularly true when considering the long‐term stability of devices. A detailed understanding of the ion migration‐driven degradation pathways is critical to design effective stabilization strategies. Nonetheless, despite substantial research in this first decade of perovskite photovoltaics, the long‐term effects of ion migration remain elusive due to the complex chemistry of lead halide perovskites. By linking materials chemistry to device optoelectronics, this study highlights that electrical bias‐induced perovskite amorphization and phase segregation is a crucial degradation mechanism in planar mixed halide perovskite solar cells. Depending on the biasing potential and the injected charge, halide segregation occurs, forming crystalline iodide‐rich domains, which govern light emission and participate in light absorption and photocurrent generation. Additionally, the loss of crystallinity limits charge collection efficiency and eventually degrades the device performance.
A multi‐technique in situ structural and optoelectronic characterization on planar perovskite solar cells reveals perovskite amorphization and phase segregation as the crucial degradation mechanisms due to ion migration on a daily timescale. The degradation has a severe negative impact on the charge collection, which reduces the photocurrent and the power conversion efficiency. The mechanism is partially reversible after rest in the dark.
Herein we report a comparative study of quaternary polymer electrolyte membranes, comprising polyethylene oxide (PEO), lithium bis(trifluoromethanesulfonyl)imide, LiTFSI(salt), SiO2-filler and ...N-methyl-N-butyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr1,4TFSI) ionic liquid. The membranes are developed in view of an efficient application in polymeric lithium battery. The study shows improvement of the ionic conductivity and the stability of the lithium interphase by increasing the Pyr1,4TFSI content up to 20% wt, as revealed by Arrhenius conductivity plots, electrochemical impedance spectroscopy as well as by cyclic test in symmetrical lithium cell. This trend is directly reflected in enhanced behavior of lithium polymer cell using LiFePO4, in terms of delivered capacity. Furthermore, the measurement indicated that setting up a proper amount of added IL is a key requirement for an optimal behavior of the electrolyte in battery.
Developing efficient wide‐bandgap perovskites is critical to exploit the benefits of a multi‐absorber solar cell and engineering commercially attractive tandem solar cells. Here, a robust, ...additive‐free, methylammonium‐free triple halide composition for the fabrication of close‐to‐ideal wide‐bandgap perovskites (1.64 eV) is reported. The introduction of low percentages of chloride into the perovskite layer avoided photoinduced halide segregation and lead to an evident improvement in the crystallization process, reaching enhanced open‐circuit voltages as high as 1.23 V. A perovskite of these characteristics is introduced for the first time in a p‐i‐n single‐junction configuration using a self‐assembled monolayer, with devices achieving photoconversion efficiencies of up to 22.6% with ultra‐high stability, retaining ≈80% of their initial efficiency after >1000 h of continuous operation unencapsulated in a nitrogen atmosphere at 85 °C. This result paves the way toward highly efficient multi‐junction tandem solar cells, bringing perovskite technology closer to commercialization.
A triple halide composition, additive‐ and methylammonium‐free, fabricates wide‐bandgap perovskites (1.64 eV). Small amounts of chloride prevent photoinduced halide segregation and improve the crystallization process significantly, enhancing open‐circuit voltages (1.23 V). These characteristics are introduced for the first time in a p‐i‐n single‐junction configuration employing a self‐assembled monolayer. Devices achieve up to 22.6% photoconversion efficiencies with exceptional stability at 85 °C.
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