Due to its outstanding optoelectronic properties, halide perovskite solar cells (PSCs) power conversion efficiency has rapidly grown to 25.7%. Nonetheless, lead poisoning is a significant hurdle to ...the deployment of perovskite solar cells (PSCs). Tin is the most alternative with the most potential due to its similar electric and electronic properties to lead and its less hazardous nature. Yet, the performance of Sn‐based PSCs lags significantly below that of Pb‐based PSCs due to the Sn (II)'s easy oxidation to Sn (IV). Incorporating large‐sized organic cations to form quasi‐two‐dimensional (2D) structured‐tin perovskites increases the stability of the PSC. In addition, the hydrophobic group of the quasi‐2D structure inhibits moisture and oxygen from penetrating the absorber layers. This review analyzes and evaluates the characteristics and performance of quasi‐2D Sn‐based perovskites such as Ruddlesden–Popper, Dion–Jacobson, and alternating cation interlayer (ACI). This work further proposes alternative strategies to improve the efficiency and stability of tin‐based PSCs, including constructing new mixed 2D/3D perovskite structures, enhancing the transmission capacity, novel organic cations, and fabricating new ACI perovskite structures and controlling perovskite strain.
Tin‐based perovskite solar cells (PSCs) experience fast crystallization and spontaneous oxidation, which act as the dominant factors causing device efficiency deterioration. Such phenomena are found to be related to the inherent properties of tin. By constructing low‐dimensional structures, the resulting devices possess improved stability and performance, highlighting the challenges and the potential for replacing lead‐based perovskite.
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.
Fluoride Chemistry in Tin Halide Perovskites Pascual, Jorge; Flatken, Marion; Félix, Roberto ...
Angewandte Chemie International Edition,
September 20, 2021, Letnik:
60, Številka:
39
Journal Article
Recenzirano
Odprti dostop
Tin is the frontrunner for substituting toxic lead in perovskite solar cells. However, tin suffers the detrimental oxidation of SnII to SnIV. Most of reported strategies employ SnF2 in the perovskite ...precursor solution to prevent SnIV formation. Nevertheless, the working mechanism of this additive remains debated. To further elucidate it, we investigate the fluoride chemistry in tin halide perovskites by complementary analytical tools. NMR analysis of the precursor solution discloses a strong preferential affinity of fluoride anions for SnIV over SnII, selectively complexing it as SnF4. Hard X‐ray photoelectron spectroscopy on films shows the lower tendency of SnF4 than SnI4 to get included in the perovskite structure, hence preventing the inclusion of SnIV in the film. Finally, small‐angle X‐ray scattering reveals the strong influence of fluoride on the colloidal chemistry of precursor dispersions, directly affecting perovskite crystallization.
Fluoride chemistry in tin halide perovskites improves the crystallization process. Fluoride anions selectively coordinate and remove SnIV and affect the colloidal properties in solution. This study describes the working mechanism of SnF2 and highlights the importance of solution chemistry for controlling crystallization and SnII oxidation in tin halide perovskites.
In 2020 dimethyl sulfoxide (DMSO), the ever‐present solvent for tin halide perovskites, was identified as an oxidant for SnII. Nonetheless, alternatives are lacking and few efforts have been devoted ...to replacing it. To understand this trend it is indispensable to learn the importance of DMSO on the development of tin halide perovskites. Its unique properties have allowed processing compact thin‐films to be integrated into tin perovskite solar cells. Creative approaches for controlling the perovskite crystallization or increasing its stability to oxidation have been developed relying on DMSO‐based inks. However, increasingly sophisticated strategies appear to lead the field to a plateau of power conversion efficiency in the range of 10–15 %. And, while DMSO‐based formulations have performed in encouraging means so far, we should also start considering their potential limitations. In this concept article, we discuss the benefits and limitations of DMSO‐based tin perovskite processing.
A dead‐end for DMSO? The crystallization of tin halide perovskites into thin‐films is uncontrolled. The strongly‐binding solvent DMSO and its tolerance to additives helped here. However, device performance stagnates around 10–15 %. The oxidation of tin by DMSO could explain this. Efforts to substitute it are promising, but still lag behind. Addressing solution properties from a fundamental perspective will allow developing DMSO‐free systems.
Daily temperature variations induce phase transitions and lattice strains in halide perovskites, challenging their stability in solar cells. We stabilized the perovskite black phase and improved ...solar cell performance using the ordered dipolar structure of β-poly(1,1-difluoroethylene) to control perovskite film crystallization and energy alignment. We demonstrated p-i-n perovskite solar cells with a record power conversion efficiency of 24.6% over 18 square millimeters and 23.1% over 1 square centimeter, which retained 96 and 88% of the efficiency after 1000 hours of 1-sun maximum power point tracking at 25° and 75°C, respectively. Devices under rapid thermal cycling between -60° and +80°C showed no sign of fatigue, demonstrating the impact of the ordered dipolar structure on the operational stability of perovskite solar cells.
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.
Tin-halide perovskites have great potential as photovoltaic materials, but their performance is hampered by undesirable oxidation of Sn(
ii
) to Sn(
iv
). In this work, we use nuclear magnetic ...resonance spectroscopy (NMR) to identify and describe the origins of Sn(
iv
) in Sn-based perovskites, mainly focusing on direct measurements of Sn oxidation states with
119
Sn-NMR in solid-state and solution. We find that dimethylsulfoxide (DMSO), a typical solvent for Sn-based perovskites, oxidizes Sn(
ii
) in acidic conditions under temperatures used for film annealing. We propose a redox reaction between DMSO and Sn(
ii
), catalyzed by hydroiodic acid, with iododimethylsulfonium iodide intermediate. We find that lower temperatures and less acidic conditions abate this reaction, and we assess a range of compositions and solution components for this instability. These results suggest the need for strategies to prevent this reaction and shed light on other solution instabilities beyond Sn(
iv
) that must be mitigated to achieve high-performance lead-free perovskites.
Tin-halide perovskites have great potential as photovoltaic materials, but their performance is hampered by undesirable oxidation of Sn(
ii
) to Sn(
iv
). NMR proves DMSO to be a main cause of oxidation.
Quasi‐2D Tin Perovskites
As the most promising alternative to lead halide perovskite, tin halide perovskite suffers from the intrinsic Sn(II) instability. Incorporating large‐sized organic cations ...forming quasi‐2D structures increases the perovskite stability. For this reason, in article number 2204233, Guixiang Li, Mahmoud H. Aldamasy, Meng Li, and co‐workers, discuss and evaluate the characteristics and challenges of quasi‐2D tin perovskites, and propose potential research strategies for opening up new opportunities of lead‐free tin‐based perovskite photovoltaics.
Current protocols for solution‐processed tin halide perovskite thin films rely on the use of DMSO. However, this solvent was recently found to oxidise tin species. This source of defects in the films ...may be the reason for the bottlenecks in device performance and reproducibility. DMSO‐free processes may avoid this problem, but lack a controlled crystallization so far. Understanding the chemistry of tin perovskites in new solvent systems would allow fabricating thin films of the highest quality.
Blue quantum dot (QD) light-emitting diodes (QLEDs) exhibit unsatisfactory operational stability and electroluminescence (EL) properties due to severe nonradiative recombination induced by large ...numbers of dangling bond defects and charge imbalance in QD. Herein, dipolar aromatic amine-functionalized molecules with different molecular polarities are employed to regulate charge transport and passivate interfacial defects between QD and the electron transfer layer (ETL). The results show that the stronger the molecular polarity, especially with the −CF3 groups possessing a strong electron-withdrawing capacity, the more effective the defect passivation of S and Zn dangling bonds at the QD surface. Moreover, the dipole interlayer can effectively reduce electron injection into QD at high current density, enhancing charge balance and mitigating Joule heat. Finally, blue QLEDs exhibit a peak external quantum efficiency (EQE) of 21.02% with an operational lifetime (T 50 at 100 cd m–2) exceeding 4000 h.
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