Selection of Functional Spacer Cations for Efficient 2D/3D Perovskite Solar Cells

In recent years,perovskite solar cells(PSCs)have gone through unparalleled rapid expansion and become a candidate for solar cells.Among various PSCs,though typical three-dimensional(3D)halide perovskite-based PSCs deliver the highest efficiency,they are subjected to severe instability,which constrains their commercializability.In comparison,two-dimensional(2D)PSCs have aroused widespread concern due to their superior stability.After that,2D/3D perovskite materials combining high efficiency and good stability have emerged as the times require,which are expected to bring about stable and efficient PSCs.Here,this review focuses on selection of functional spacer cations for efficient and stable 2D/3D PSCs.First,the unique function of different spacer groups and the selection of appropriate spacer cations in 2D perovskites is summarized and proposed.Then,by selecting appropriate cations,the role of 2D perovskites is elaborated,including energy level regulation,ion migration suppression,defect passivation,residual stress release and improved stability.In addition,the preparation methods of 2D/3D perovskites are comprehensively summarized.Finally,current challenges and future opportunities for the further development of 2D/3D perovskites for solar cells are discussed and prospected.

Highly efficient perovskite solar cells by building 2D/3D perovskite heterojuction in situ for interfacial passivation and energy level adjustment

Passivating the interfacial defects and reducing the interfacial non-radiative recombination losses are the keys to improving the photovoltaic performance of three-dimensional(3D)perovskite solar cells(PVSCs).Stacking two dimensional(2D)perovskites on 3D perovskite is a promising method for interfacial treatment that improves the stability and efficiency of PVSCs.Herein,we developed conjugated fluorinated benzimidazolium cation(FBIm+)which can be inserted between 3D perovskite and holetransporting layer(HTL)to form 2D perovskite in situ.The 2D single crystal structures of(FBIm)_(2)Pb I4and(FBIm)_(2)Pb Br_(4)were achieved and confirmed by single-crystal X-ray diffraction(XRD),while few single crystals of 2D perovskite based on imidazolium or benzimidazolium anchors have been reported.The 2D perovskite can passivate the interfacial defects,induce better crystallinity and orientation,conduct lower trap density and extend carrier lifetime.Furthermore,the energy level arrangement can be regulated by changing the counterion from iodide to bromide,which can efficiently improve the hole extraction and device performances.As a consequence,the best efficiency of 23.00%for FBIm Br-incorporated devices was achieved,while only 20.72%for the control device.Meanwhile,the PVSCs modified by FBIm Br displayed excellent environmental stability due to the constructed hydrophobic 2D perovskite layer which can effectively block moisture permeation.This work develops a new path to design novel conjugated organic passivants to form 2D/3D perovskite structures.

Ion migration in 3D metal halide perovskite field effect transistors

3D perovskite materials are advancing rapidly in the field of photovoltaics and light-emitting diodes,but the development in field effect transistors(FETs)is limited due to their intrinsic ion migration.Ion migration in perovskite FETs can screen the electric field of the gate and affect its modulation,as well as influence the charge carriers transport,leading to non-ideal device characteristics and lower device stability.Here,we provide a concise review that explains the mechanism of ion migration,summarizes the strategies for suppressing ion migration,and concludes with a discussion of the future prospects for 3D perovskite FETs.

Chlorine‑Rich Substitution Enabled 2D3D Hybrid Perovskites for High Efficiency and Stability in Sn‑Based Fiber‑Shaped Perovskite Solar Cells

Despite the impressive power conversion efficiency(PCE)beyond 25.5%,perovskite solar cells,especially the Sn-based variants,are poorly stable under normal operating conditions compared with the market-dominant silicon solar cells that can last for over 25 years.2D3D hybrid perovskite materials are one of the best options to overcome the instability chal-lenge without compromising efficiency.Indeed,a record performance of 1 year was reported in Pb-based 2D3D planar per-ovskite devices.However,the reaction between 2 and 3D perovskite molecules requires high temperatures(-300°C)and increased reaction time(-24 h)to achieve high-quality 2D3D hybrid perovskites.Herein,we base on the ability of chlorine to displace iodine from its ionic compounds in solutions to utilize chloride ions as catalysts for speeding up the reaction between iodine-based 2D and 3D perovskite molecules.The approach reduces the reaction time to-20 min and the reaction temperature to-100°C with the formation of high-quality 2D3D hybrid perovskites,free from pure 2D traces.Integrating the synthesized 2D3D hybrid perovskite material with 50%chlorine doping in a fiber-shaped solar cell architecture yielded the highest reported PCE of 11.96%in Sn-based fiber-shaped perovskite solar cells.The unencapsulated and encapsulated fiber-shaped solar cells could maintain 75%and 95.5%of their original PCE,respectively,after 3 months under room light and relative humidity of 35–40%,revealing the champion stability in Sn-based perovskite solar devices.The solar yarn also demonstrated constant energy output under changing light incident angles(0–180°).

Hydrophobic long alkyl chain organic cations induced 2D/3D heterojunction for efficient and stable perovskite solar cells

Designing post-formed two-dimensional(2D)perovskite on the surface of three-dimensional(3D)perovskite with matched energy levels and high stability is crucial for improving the performance and stability of perovskite solar cells(PSCs).Herein,a long alkyl chain dodecylammonium bromide(DABr)was applied to react with excessive lead iodide(PbI_(2))on the grain boundary of metal halide perovskite preferentially,forming DA_(2)PbI_(4)(n=1)to constitute a clear 2D/3D heterojunction.The existence of heterojunction increases the intensity of the built-in electric field of the device to enhance carrier separation and extraction,and the amino group of dodecylammonium cation passivates defects,which jointly contribute to the improvement of the power conversion efficiency(PCE)from 20.35 to 21.81%.The long alkyl chain endows the 2D perovskite with good hydrophobic properties,improving the humidity and thermal stability of the device.The unencapsulated device can maintain 64%of its initial efficiency after 1065 h storage in ambient air.

Recent Application and Progress of Metal Halide Perovskite Photodetector on Flexible Substrates

In recent years,flexible photodetectors(FPDs)have received increasing attention due to their applications in electronic eyes,flexible sensing,terminal devices,and wearable devices.In addition,metallic halide perovskite materials are considered as future materials for FPDs due to their compatibility with flexible substrates,low cost,simple synthesis methods,and superior optoelectronic properties.This review provides a comprehensive overview of the relevant cutting-edge research in the field of flexible perovskite photodetectors(FPPDs)from 2020 to 2022.First,the evaluation criteria for FPPDs are discussed and the development of perovskite stability criteria is emphatically described.Afterwards,the synthesis methods and device construction processes of metal halide perovskite materials commonly used by researchers in the past three years are described.These include single crystals and low-dimensional materials.Moreover,we have elaborated on the research of self-powered FPPD and its contributions in wearability,terminals,and portability.Finally,a summary of developments and possibilities in the field of FPPDs from 2020 to 2022 is provided.

Ionic liquid engineering enabled in-plane orientated 1D perovskite nanorods for efficient mixed-dimensional perovskite photovoltaics

Mixed-dimensional engineering of perovskite material has been demonstrated as a facile and promising strategy to improve both photovoltaic performance and long-term stability of perovskite solar cells(PSCs).In this study,we report an in-plane preferred orientation of 1D perovskite induced by an ionic liquid(IL)of 1-(3-cyanopropyl)-3-methylimidazolium chloride(CPMIMCl)for the first time via sequential deposition approach,leading to a mixed dimensional perovskite thin films.The generated one-dimensional(1D)CPMIMPbI3 with in-plane orientation resides at the grain boundaries of three-dimensional(3D)perovskite can be appreciably observed from the morphology level,leading to creation of high-quality films with large grain size with more efficient defect passivation.Moreover,the dispersion of IL in the bulk phase of perovskite material allows for the formation of 1D perovskite for multiple level passivation to inhibit non-radiative recombination and optimize carrier transport.This IL engineering strategy not only yields a mixed-dimensional perovskite heterostructure with in-plane orientation 1D perovskite nano-rods but also significantly improves the opto-electronic property with suppressed trap states.As a result,the CPMIMCl-treated PSCs show an enhanced photovoltaic performance with a champion power conversion efficiency(PCE)up to 24.13%.More importantly,benefiting from the hydrophobicity of formed 1D perovskite and defects suppression,the corresponding PSC demonstrates an excellent longterm stability and maintain 97.1%of its pristine PCE at 25C under 50%RH condition over 1000 h.This research provides an innovative perspective for employing the low dimensional engineering to optimize the performance and stability of photovoltaic devices.

Reductive ionic liquid-mediated crystallization for enhanced photovoltaic performance of Sn-based perovskite solar cells

Tin(Sn)-based perovskite solar cells(PSCs)have recently made inspiring progress,and certified power conversion efficiency(PCE)has reached impressive value of 14.8%.However,it is still challenging to realize efficient and stable 3D Sn-based PSCs due to the fast crystallization and easy Sn^(2+)oxidation of Sn-based perovskite.Herein,we reported the utilization of a reductive ionic liquid,methylamine formate(MAFa),to drive the controlled crystallization process and suppress Sn^(2+)oxidation of FASnI_(3)perovskite film.The coordination of C=O and Sn^(2+)and the hydrogen bonding of N-H···I between the MAFa and FASnI_(3)precursors are shown to be responsible for retarding the crystallization of FASnI_(3)during film-forming process,which promotes the oriented growth and reduced defect traps of the film.Moreover,the strong reducibility of–CHO groups in Fa−suppresses the oxidation of Sn^(2+)in the film.As a result,MAFa-modified 3D PSCs device could reach champion PCE of up to 8.50%,which is enhanced by 26.11%compared to the control device with PCE of 6.74%.Most importantly,the MAFa-modified device shows much improved stability compared to the control device under same conditions without encapsulation.This work adds key building blocks for further boosting the PCE and stability of Sn-based PSCs.