Characterization of structural transitions and lattice dynamics of hybrid organic–inorganic perovskite CH3NH3PbI3

By combining temperature-dependent x-ray diffraction(XRD) with temperature-dependent Raman scattering, we have characterized the structural transitions and lattice dynamics of the hybrid organic–inorganic perovskite CH3NH3PbI3.The XRD measurements cover distinct phases between 15 K and 370 K and demonstrate a general positive thermal expansion.Clear anomalies are found around the transition temperatures.The temperature evolution of the lattice constants reveals that the transition at 160 K/330 K is of the first-/second-order type.Raman measurements uncover three strong lowfrequency modes, which can be ascribed to the vibration of the Pb/I atoms.The temperature evolution of the modes clearly catches these transitions at 160 K and 330 K, and confirms the transition types, which are exactly consistent with the XRD results.The present study may set an experimental basis to understand the high conversion efficiency in methylammonium lead iodide.

Cross-layer all-interface defect passivation with pre-buried additive toward efficient all-inorganic perovskite solar cells

The buried interface in the perovskite solar cell(PSC)has been regarded as a breakthrough to boost the power conversion efficiency and stability.However,a comprehensive manipulation of the buried interface in terms of the transport layer,buried interlayer,and perovskite layer has been largely overlooked.Herein,we propose the use of a volatile heterocyclic compound called 2-thiopheneacetic acid(TPA)as a pre-buried additive in the buried interface to achieve cross-layer all-interface defect passivation through an in situ bottom-up infiltration diffusion strategy.TPA not only suppresses the serious interfacial nonradiative recombination losses by precisely healing the interfacial and underlying defects but also effectively enhances the quality of perovskite film and releases the residual strain of perovskite film.Owing to this versatility,TPA-tailored CsPbBr3 PSCs deliver a record efficiency of 11.23% with enhanced long-term stability.This breakthrough in manipulating the buried interface using TPA opens new avenues for further improving the performance and reliability of PSC.

Reinforced SnO_(2) tensile-strength and“buffer-spring”interfaces for efficient inorganic perovskite solar cells

Suppressing nonradiative recombination and releasing residual strain areprerequisites to improving the efficiency and stability of perovskite solar cells(PSCs).Here,long-chain polyacrylic acid(PAA)is used to reinforce SnO_(2)film and passivate SnO_(2)defects,forming a structure similar to“reinforcedconcrete”with high tensile strength and fewer microcracks.Simultaneously,PAA is also introduced to the SnO_(2)/perovskite interface as a“buffer spring”torelease residual strain,which also acts as a“dual-side passivation interlayer”to passivate the oxygen vacancies of SnO_(2)and Pb dangling bonds in halideperovskites.As a result,the best inorganic CsPbBr_(3)PSC achieves a championpower conversion efficiency of 10.83%with an ultrahigh open-circuit voltageof 1.674 V.The unencapsulated PSC shows excellent stability under 80%relative humidity and 80℃over 120 days.

Synergistic Optimization of Buried Interface by Multifunctional Organic-Inorganic Complexes for Highly Efficient Planar Perovskite Solar Cells

For the further improvement of the power conversion efficiency(PCE)and stability of perovskite solar cells(PSCs),the buried interface between the perovskite and the electron transport layer is crucial.However,it is challenging to effectively optimize this interface as it is buried beneath the perovskite film.Herein,we have designed and synthesized a series of multifunctional organic-inorganic(OI)complexes as buried interfacial material to promote electron extraction,as well as the crystal growth of the perovskite.The OI complex with BF4−group not only eliminates oxygen vacancies on the SnO_(2) surface but also balances energy level alignment between SnO_(2) and perovskite,providing a favorable environment for charge carrier extraction.Moreover,OI complex with amine(−NH_(2))functional group can regulate the crystallization of the perovskite film via interaction with PbI2,resulting in highly crystallized perovskite film with large grains and low defect density.Consequently,with rational molecular design,the PSCs with optimal OI complex buried interface layer which contains both BF4−and−NH_(2) functional groups yield a champion device efficiency of 23.69%.More importantly,the resulting unencapsulated device performs excellent ambient stability,maintaining over 90%of its initial efficiency after 2000 h storage,and excellent light stability of 91.5%remaining PCE in the maximum power point tracking measurement(under continuous 100 mW cm−2 light illumination in N2 atmosphere)after 500 h.

4‑Terminal Inorganic Perovskite/Organic Tandem Solar Cells Offer 22%Efficiency

After fast developing of single-junction perovskite solar cells and organic solar cells in the past 10 years,it is becoming harder and harder to improve their power conversion efficiencies.Tandem solar cells are receiving more and more attention because they have much higher theoretical efficiency than single-junction solar cells.Good device performance has been achieved for perovskite/silicon and perovskite/perovskite tandem solar cells,including 2-terminal and 4-terminal structures.However,very few studies have been done about 4-terminal inorganic perovskite/organic tandem solar cells.In this work,semi-transparent inorganic perovskite solar cells and organic solar cells are used to fabricate 4-terminal inorganic perovskite/organic tandem solar cells,achieving a power conversion efficiency of 21.25%for the tandem cells with spin-coated perovskite layer.By using drop-coating instead of spin-coating to make the inorganic perovskite films,4-terminal tandem cells with an efficiency of 22.34%are made.The efficiency is higher than the reported 2-terminal and 4-terminal inorganic perovskite/organic tandem solar cells.In addition,equivalent 2-terminal tandem solar cells were fabricated by connecting the sub-cells in series.The stability of organic solar cells under continuous illumination is improved by using semi-transparent perovskite solar cells as filter.

Inorganic Halide Perovskite Quantum Dots:A Versatile Nanomaterial Platform for Electronic Applications

Metal halide perovskites have generated significant attention in recent years because of their extraordinary physical properties and photovoltaic performance.Among these,inorganic perovskite quantum dots(QDs)stand out for their prominent merits,such as quantum confinement effects,high photoluminescence quantum yield,and defect-tolerant structures.Additionally,ligand engineering and an all-inorganic composition lead to a robust platform for ambient-stable QD devices.This review presents the state-of-the-art research progress on inorganic perovskite QDs,emphasizing their electronic applications.In detail,the physical properties of inorganic perovskite QDs will be introduced first,followed by a discussion of synthesis methods and growth control.Afterwards,the emerging applications of inorganic perovskite QDs in electronics,including transistors and memories,will be presented.Finally,this review will provide an outlook on potential strategies for advancing inorganic perovskite QD technologies.

Dimethylammonium cation stabilizes all-inorganic perovskite solar cells

Facing the poor environmental stability of traditional methylammonium or formamidinium-based lead halide per-ovskites,scientists turn their attention to inorganic lead hal-ide perovskites(ILHPs)with narrow bandgaps,excellent thermal stability and reduced ion migration compared to their organic/inorganic counterparts[1−4].Up to now,the PCEs for ILHP solar cells exceed 21%[5].Especially,the preferred black ILHP(e.g.CsPbI3)with the smallest bandgap of~1.7 eV and single-halide composition for avoiding phase separation is crucial for high-performance single-junction solar cells and can be applied in tandem devices as the top cells[6,7].However,small Cs+(167 pm)in CsPbI3 with a tolerance factor close to 0.8 is unsuitable for the 3D PbI3-framework[8].The mis-matched size of cations will induce lattice strain and the per-ovskite spontaneously transforms to undesired non-photoact-ive yellow phase(δ-phase,like NH4CdCl3)(Fig.1(a))[9,10].There-fore,improving lattice symmetry and reducing lattice strain are the strategies for inhibiting the phase transition of ILHPs.

Molecular Structure Tailoring of Organic Spacers for High‑Performance Ruddlesden–Popper Perovskite Solar Cells

Layer-structured Ruddlesden–Popper(RP)perovskites(RPPs)with decent stability have captured the imagination of the photovoltaic research community and bring hope for boosting the development of perovskite solar cell(PSC)technology.However,two-dimensional(2D)or quasi-2D RP PSCs are encountered with some challenges of the large exciton binding energy,blocked charge transport and poor film quality,which restrict their photovoltaic performance.Fortunately,these issues can be readily resolved by rationally designing spacer cations of RPPs.This review mainly focuses on how to design the molecular structures of organic spacers and aims to endow RPPs with outstanding photovoltaic applications.We firstly elucidated the important roles of organic spacers in impacting crystallization kinetics,charge transporting ability and stability of RPPs.Then we brought three aspects to attention for designing organic spacers.Finally,we presented the specific molecular structure design strategies for organic spacers of RPPs aiming to improve photovoltaic performance of RP PSCs.These proposed strategies in this review will provide new avenues to develop novel organic spacers for RPPs and advance the development of RPP photovoltaic technology for future applications.

Semitransparent organic photovoltaics enabled by transparent p-type inorganic semiconductor and near-infrared acceptor

Semitransparent organic photovoltaics(STOPVs)have gained wide attention owing to their promising applications in building-integrated photovoltaics,agrivoltaics,and floating photovoltaics.Organic semiconductors with high charge carrier mobility usually have planar and conjugated structures,thereby showing strong absorption in visible region.In this work,a new concept of incorporating transparent inorganic semiconductors is proposed for high-performance STOPVs.Copper(I)thiocyanate(CuSCN)is a visible-transparent inorganic semiconductor with an ionization potential of 5.45 eV and high hole mobility.The transparency of CuSCN benefits high average visible transmittance(AVT)of STOPVs.The energy levels of CuSCN as donor match those of near-infrared small molecule acceptor BTP-eC9,and the formed heterojunction exhibits an ability of exciton dissociation.High mobility of CuSCN contributes to a more favorable charge transport channel and suppresses charge recombination.The control STOPVs based on PM6/BTP-eC9 exhibit an AVT of 19.0%with a power conversion efficiency(PCE)of 12.7%.Partial replacement of PM6 with CuSCN leads to a 63%increase in transmittance,resulting in a higher AVT of 30.9%and a comparable PCE of 10.8%.

Defect engineering on all-inorganic perovskite solar cells for high efficiency

Perovskite solar cells based on organic–inorganic hybrid perovskite materials have become a research hotspot in photovoltaics field due to their outstanding power conversion efficiency (PCE)[1]. Nonetheless, the organic cations are volatile and have rotation freedom, which is not good for photoand thermal-stability of the devices.

Inorganic perovskite/organic tandem solar cells with efficiency over 20%

The rapid development of perovskite solar cells is beyond our imagination.The power conversion efficiency(PCE)of organic-inorganic hybrid perovskite solar cells has reached 25.5%(https://www.nrel.gov/pv/cell-efficiency.html).However,the unsatisfactory stability of hybrid perovskites is an obstacle for their commercialization,which results from the volatile and hygroscopic organic cations[1].

Antioxidative solution processing yields exceptional Sn(Ⅱ) stability for sub-1.4 eV bandgap inorganic perovskite solar cells

Owing to the combined features of sub-1.4 eV bandgap and all-inorganic composition,cesium tin–lead(Sn-Pb)triiodide perovskite is promising for approaching the Shockley-Queisser limit of solar cells while avoiding the use of volatile organic cations.But the low Sn(Ⅱ)stability in this perovskite remains a hurdle for delivering its theoretically attainable device performance.Herein we present a synthesis method of this perovskite based on an acetylhydrazine-incorporated antioxidative solution system.Mechanistic investigation shows that acetylhydrazine effectively reduces the oxidation of solution-phase Sn(Ⅱ)and meanwhile creates an electron-rich,protective nano-environment for solid-state Sn(Ⅱ)ions.These lead to high oxidation resistance of the final film as well as effective defect inhibition.The resultant solar cells demonstrate power conversion efficiencies up to 15.04%,the highest reported so far for inorganic perovskite devices with sub-1.4 eV bandgaps.Furthermore,the T_(90) lifetime of these devices can exceed 1000 hours upon light soaking in a nitrogen atmosphere,demonstrating the potential advantage when lower-bandgap perovskite solar cells go all-inorganic.

Unraveling Passivation Mechanism of Imidazolium-Based Ionic Liquids on Inorganic Perovskite to Achieve Near-Record-Efficiency CsPbI_(2)Br Solar Cells

The application of ionic liquids in perovskite has attracted wide-spread attention for its astounding performance improvement of perovskite solar cells(PSCs).However,the detailed mechanisms behind the improvement remain mysterious.Herein,a series of imidazolium-based ionic liquids(IILs)with different cations and anions is systematically investigated to elucidate the passivation mechanism of IILs on inorganic perovskites.It is found that IILs display the following advantages:(1)They form ionic bonds with Cs^(+)and Pb^(2+)cations on the surface and at the grain boundaries of perovskite films,which could effectively heal/reduce the Cs^(+)/I−vacancies and Pb-related defects;(2)They serve as a bridge between the perovskite and the hole-transport-layer for effective charge extraction and transfer;and(3)They increase the hydrophobicity of the perovskite surface to further improve the stability of the CsPbI_(2)Br PSCs.The combination of the above effects results in suppressed non-radiative recombination loss in CsPbI_(2)Br PSCs and an impressive power conversion efficiency of 17.02%.Additionally,the CsPbI_(2)Br PSCs with IILs surface modification exhibited improved ambient and light illumination stability.Our results provide guidance for an indepth understanding of the passivation mechanism of IILs in inorganic perovskites.

Preventing inhomogeneous elemental distribution and phase segregation in mixed Pb-Sn inorganic perovskites via incorporating PbS quantum dots

Inhomogeneous Pb/Sn elemental distribution and the resulted phase segregation in mixed Pb-Sn halide perovskites would result in energy disorder(band structure and phase distribution disorder),which greatly limits their photovoltaic performance.Here,Pb S quantum dot has been synthesized and demonstrated as seeds for modulation crystallization dynamics of the mixed Pb-Sn inorganic perovskites,allowing an enhanced film quality and significantly suppressing phase segregation.With this additive power conversion efficiency of 8%and 6%is obtained under irradiation of full sunlight in planar and mesoporous structured solar cells in combination with CsPb_(0.5) Sn_(0.5)I_(2)Br inorganic perovskite,respectively.Our finding reveals exploring the actual Pb/Sn atoms location in perovskite structure and its influence on developing efficient and stable low-bandgap perovskite solar cells.

Alkali metal cation engineering in organic/inorganic hybrid perovskite solar cells

The past decade has witnessed the rapid advance in organic–inorganic hybrid perovskite solar cells(PSCs).Owing to unique optoelectronic properties of perovskites,the power conversion efficiency(PCE)of PSCs has jumped from 3.8%to25.5%[1–4].However,under the stimulus of illumination,moisture,oxygen and heat,perovskites exhibit unsatisfactory stability due to weak bonding among the components in these soft-lattice crystals[5–7].Doping and passivation engineering with alkali metal cations can enhance the intrinsic stability of perovskite materials.Here,the recent progress of alkali metal cations engineering is reviewed,and the impact on the crystallization,lattice structure,photovoltaic performance and stability is discussed.

Synergistic stabilization of CsPbI_(3) inorganic perovskite via 1D capping and secondary growth

Cesium lead iodide(CsPbI_(3)) perovskite has gained great attention in the photovoltaic(PV) community because of its unique optoelectronic properties, good chemical stability and appropriate bandgap for sunlight harvesting applications. However, compared to solar cells fabricated from organic-inorganic hybrid perovskites, the commercialization of devices based on all-inorganic CsPbI_(3) perovskites still faces many challenges regarding PV performance and long-term stability. In this work, we discovered that tetrabutylammonium bromide(TBABr) post-treatment to CsPbI_(3) perovskite films could achieve synergistic stabilization with both TBA+cation intercalation and Br-doping. Such TBA^(+) cation intercalation leads to onedimensional capping with TBAPb I3 perovskite formed in situ, while the Br-induced crystal secondary growth helps effectively passivate the defects of CsPbI_(3) perovskite, thus enhancing the stability. In addition, the incorporation of TBABr can improve energy-level alignment and reduce interfacial charge recombination loss for better device performance. Finally, the highly stable TBABr-treated CsPbI_(3)-based perovskite solar cells show reproducible photovoltaic performance with a champion efficiency up to 19.04%, while retaining 90% of the initial efficiency after 500 h storage without encapsulation.

Making fully printed perovskite solar cells stable outdoor with inorganic superhydrophobic coating

Outdoor environment including moisture, dust, UV, oxygen and thermal stress(repeated heating-cooling)is devastating to perovskite solar cells(PSCs). Here, we demonstrate a new strategy to make fully printed PSCs stable with maximum power output in outdoor environment by coating them with a porous hydrophobic inorganic layer. After coating, the PSCs can maintain superior stability of more than 150 days of outdoor storage, 240 h of continuous operation at the maximum power output point in ambient air with relative humidity as high as ~80%, and stable operation for more than 10 h under raining condition. ANSYS simulation shows that the thin and porous nature of the inorganic coating layer offers much better heat dissipation than conventional encapsulation methods using glasses attached by photocurable epoxy. A similar thermal expansion coefficient of the inorganic encapsulation material with the solar cell substrate can also prevent it from cracking after repeated heating-cooling cycles. All of these merits resulted from our encapsulation method endow the perovskite solar cells with the real outdoor working capability.

Ferroelectric Properties and Applications of Hybrid Organic-Inorganic Perovskites

Hybrid organic-inorganic perovskites （e.g. CH;NH;PbI;） have attracted tremendous attention due to their promise for achieving next-generation cost-effective and high performance optoelectronic devices.These hybrid organic-inorganic perovskites possess excellent optical and electronic properties, including strong light absorption, high carrier abilities, optimized charge diffusion lengths, and reduced charge recombination etc., leading to their widespread applications in advanced solar energy technologies （e.g.high efficiency perovskite solar cells）. However, there is still a lack of investigations regarding fundamental properties such as ferroelectricity in these perovskites.As conventional ferroelectric ceramics are prepared at high temperature and have no mechanically flexibility,low-temperature proceed and flexible perovskite ferroelectrics have become promising candidates and should be exploited for future flexible ferroelectric applications. Here, ferroelectric properties in hybrid organic-inorganic perovskites and several state-of-the-art perovskite ferroelectrics are reviewed. Novel ferroelectric applications of hybrid organic-inorganic perovskites are discussed as well, providing guideline for realizing future high performance and flexible ferroelectric devices.

Inorganic CsPbI3 Perovskites toward High-Efficiency Photovoltaics

The organic–inorganic hybrid perovskite solar cells(PSCs)have demonstrated their unprecedented high efficiency and potential for commercialization.The volatile organic components in the hybrid perovskite crystal structure are still a big challenge for long-term stabilities.Recently,inorganic CsPbI3 perovskite has attracted much attention because of its superior chemical stability over the prevailing hybrid organic–inorganic perovskite and the most suitable band gap among all-inorganic perovskites.Nevertheless,CsPbI3 suffers from phase instability and low photovoltaic(PV)performance due to its undesirable tolerant factor.Much research effort has been devoted into stabilization of CsPbI3.In this perspective,we review the recent progress on chemical engineering processes for the stabilization of inorganic CsPbI3 perovskite for high-efficiency PVs.We also discuss the importance of understanding mechanism behind stabilization of CsPbI3 perovskite film and the development of inorganic CsPbI3-based highly efficient and stable PSCs.

Photodetectors based on inorganic halide perovskites:Materials and devices

The newly emerging metal halide perovskites have attracted considerable attention due to their exceptional optoelectronic properties. This upsurge was initially driven when the power conversion efficiency of perovskite-based photovoltaic devices exceeded 23%. Due to their optoelectronic properties, perovskite materials have also been used in light-emitting diodes, photodetectors, lasers, and memory devices. This study comprehensively discusses the recent progress of allinorganic perovskite-based photodetectors, focusing on their structures, morphologies of their constituent materials, and diverse device architectures that improve the performance metrics of these photodetectors. A brief outlook, highlighting the main existing problems, possible solutions to these problems, and future development directions, is also provided herein.