The Main Progress of Perovskite Solar Cells in 2020-2021

Perovskite solar cells(PSCs)emerging as a promising photovoltaic technology with high efficiency and low manufacturing cost have attracted the attention from all over the world.Both the efficiency and stability of PSCs have increased steadily in recent years,and the research on reducing lead leakage and developing eco-friendly lead-free perovskites pushes forward the commercialization of PSCs step by step.This review summarizes the main progress of PSCs in 2020 and 2021 from the aspects of efficiency,stability,perovskite-based tandem devices,and lead-free PSCs.Moreover,a brief discussion on the development of PSC modules and its challenges toward practical application is provided.

Humanoid Intelligent Display Platform for Audiovisual Interaction and Sound Identification

This study proposes a rational strategy for the design,fabrication and system integration of the humanoid intelligent display platform(HIDP)to meet the requirements of highly humanized mechanical properties and intelligence for human-machine interfaces.The platform’s sandwich structure comprises a middle lightemitting layer and surface electrodes,which consists of silicon elastomer embedded with phosphor and silk fibroin ionoelastomer,respectively.Both materials are highly stretchable and resilient,endowing the HIDP with skin-like mechanical properties and applicability in various extreme environments and complex mechanical stimulations.Furthermore,by establishing the numerical correlation between the amplitude change of animal sounds and the brightness variation,the HIDP realizes audiovisual interaction and successful identification of animal species with the aid of Internet of Things(IoT)and machine learning techniques.The accuracy of species identification reaches about 100%for 200 rounds of random testing.Additionally,the HIDP can recognize animal species and their corresponding frequencies by analyzing sound characteristics,displaying real-time results with an accuracy of approximately 99%and 93%,respectively.In sum,this study offers a rational route to designing intelligent display devices for audiovisual interaction,which can expedite the application of smart display devices in human-machine interaction,soft robotics,wearable sound-vision system and medical devices for hearing-impaired patients.

Theoretical Study of Using Kinetics Strategy to Enhance the Stability of Tin Perovskite

Tin perovskite solar cell received great attention in recent years owing to its optimum bandgap and heavy metal-free property.The main concern for the development of tin perovskite is the oxidation from Sn^(2+)to Sn^(4+).Herein,we report a surface hetero-protection strategy to avoid the surface reaction of tin perovskite.Three types of materials,including low-dimensional tin perovskite,alkali metal halide,and oxides of group IVA element,are exploited as protecting materials on tin perovskite surface with first-principles calculation.The lattice mismatch,oxidation resistance,and interface stability of these materials are investigated to search for ideal protecting-layer materials.After screening over 30 candidates,we finally obtain 8 suitable materials(SiO_(2),GeO_(2),KCl,Na Br,Cs F,Li F,Li I,CsSn_(2)Br_(5))for hetero-protection of tin perovskite.To further understand their application potential in a solar cell device,we then calculate the property of charge transfer between the interface of these materials and tin perovskite.Our study provides a guide for the experimental realization of efficient and stable tin perovskite solar cell.

Ligand Engineering in Tin-Based Perovskite Solar Cells

Perovskite solar cells(PSCs)have attracted aggressive attention in the photovoltaic field in light of the rapid increasing power conversion efficiency.However,their large-scale application and commercialization are limited by the toxicity issue of lead(Pb).Among all the lead-free perovskites,tin(Sn)-based perovskites have shown potential due to their low toxicity,ideal bandgap structure,high carrier mobility,and long hot carrier lifetime.Great progress of Sn-based PSCs has been realized in recent years,and the certified efficiency has now reached over 14%.Nevertheless,this record still falls far behind the theoretical calculations.This is likely due to the uncontrolled nucleation states and pronounced Sn(Ⅳ)vacancies.With insights into the methodologies resolving both issues,ligand engineering-assisted perovskite film fabrication dictates the state-of-the-art Sn-based PSCs.Herein,we summarize the role of ligand engineering during each state of film fabrication,ranging from the starting precursors to the ending fabricated bulks.The incorporation of ligands to suppress Sn~(2+)oxidation,passivate bulk defects,optimize crystal orientation,and improve stability is discussed,respectively.Finally,the remained challenges and perspectives toward advancing the performance of Sn-based PSCs are presented.We expect this review can draw a clear roadmap to facilitate Sn-based PSCs via ligand engineering.

Performance enhancement of perovskite solar cells:surface is the key

Metal halide perovskite solar cells(PSCs)stand out as one of the most promising contenders among photovoltaic technologies for the future.Over the past decade,PSCs with high power conversion efficiency(PCE)predominantly adopted the normal(ni-p)device structure.However,a common p-type organic small molecule,Spiro-OMe TAD,which is widely employed at the top layer of n-i-p devices[1],faces issues such as susceptibility to water absorption and poor thermal stability.

Recent progress in perovskite solar cells:material science

Perovskite solar cells represent a promising third-generation photovoltaic technology with low fabrication cost and high power conversion efficiency.In light of the rapid development of perovskite materials and devices,a systematic survey on the latest advancements covering a broad range of related work is urgently needed.This review summarizes the recent major advances in the research of perovskite solar cells from a material science perspective.The discussed topics include the devices based on different type of perovskites(organic-inorganic hybrid,all-inorganic,and lead-free perovskite and perovskite quantum dots),the properties of perovskite defects,different type of charge transport materials(organic,polymeric,and inorganic hole transport materials and inorganic and organic electron transport materials),counter electrodes,and interfacial materials used to improve the efficiency and stability of devices.Most discussions focus on the key progresses reported within the recent five years.Meanwhile,the major issues limiting the production of perovskite solar cells and the prospects for the future development of related materials are discussed.

Perovskite nanocrystals:synthesis,properties and applications

Halide perovskites have emerged as superstar materials for optoelectronic devices. Besides the fever of research in solar cells, these materials show great promise on light emitting diodes(LEDs), photodetectors and lasers as well. Rapid advances in bulk perovskite materials aroused universal interest for the development of perovskite nanocrystals, inspired by the great progress of classic colloidal semiconductor quantum dots. Perovskite nanocrystals have been synthesized based on solution process and exhibited high luminescence quantum yield, sharp emission peak, and emission color tunability. Significant progresses have been made about the application of perovskite nanocrystals for LED and lasers in recent years. In this paper, we will comprehensively introduce the synthesis strategies, physical and chemical characteristics, as well as their applications in optoelectronic devices.

Stability improvement under high efficiency—next stage development of perovskite solar cells

With efficiency of perovskite solar cells(PSCs) overpassing 23%, to realize their commercialization, the biggest challenge now is to boost the stability to the same level as conventional solar cells. Thus, tremendous effort has been directed over the past few years toward improving the stability of these cells. Various methods were used to improve the stability of bulk perovskites,including compositional engineering, interface adjustment, dimensional manipulation, crystal engineering, and grain boundary decoration. Diverse device configurations, carrier transporting layers, and counter electrodes are investigated. To compare the stability of PSCs and clarify the degradation mechanism, diverse characterization methods were developed. Overall stability of PSCs has become one central topic for the development of PSCs. In this review, we summarize the state-of-the-art progress on the improvement of device stability and discuss the directions for future research, hoping it provides an overview of the current status of the research on the stability of PSCs and guidelines for future research.

Efficient defect-controlled photocatalytic hydrogen generation based on near-infrared Cu-In-Zn-S quantum dots

The development of photocatalysts that can effectively harvest visible light is essential for advances in high-efficiency solar-driven hydrogen generation. Herein, we synthesized water soluble CuInS2 （CIS） and Cu-In-Zn-S （CIZS） quantum dots （QDs） by using one-pot aqueous method. The CIZS QDs are well passivated by glutathione ligands and are highly stable in aqueous conditions. We subsequently applied these QDs as a light harvesting material for photocatalytic hydrogen generation. Unlike most small band gap materials that show extremely low efficienc36 these new QDs display remarkable energy conversion efficiency in the visible and near-infrared regions. The external quantum efficiency at 650 nm is - 1.5%, which, to the best of our knowledge, is the highest value achieved until now in the near-infrared region.

Strategies for enhancing the stability of metal halide perovskite towards robust solar cells

Perovskite is rising as the most promising material for the next generation of solar cells,due to its high efficiency,low cost,and convenient fabrication.However,the stability of perovskite solar cells remains to be a challenge towards large-scale application.Perovskite materials play a key role in improving the stability of PSCs,and tremendous efforts have been committed to stabilizing the perovskite materials,including composition regulation,crystallization control,and interface optimization.Herein we review the state-of-the-art strategies to improve the stability of perovskite layers in PSCs,and important strategies are highlighted.We analyze in-depth the influence of each site ion on perovskite structural stability and summarize the important progress of these structures showing superior stability.We then summarize the use of additives to regulate perovskite crystallization and defect passivation and elaborate the related mechanisms.Furthermore,the pros and cons of different interface treatment methods used in perovskite solar cells are discussed。

Low-dimensionality perovskites yield high electroluminescence

Light-emitting diodes(LEDs)are changing the energy and lighting industry due to their high power efficiencies,low energy consumption,and long operational lifetimes.While epitaxiallygrown LEDs are the current industry standard,their incompatibility with large-area displays and flexible substrates precludes their use in many applications.Solution-processed light-emitting materials are more versatile and can be easily coated onto a variety of substrates using modern deposition techniques such as vapor deposition,spin-coating,dip-coating,and spray-painting.With these advantages,organic light-emitting diodes(OLEDs)have been widely applied to TVs,cell phones,and semi-transparent displays.They,however,suffer from resolution-transparency trade-off and incompatibility with high-temperature processes.Quantum dot(QD)light-emitting diodes(QLEDs)have sharper emission features and higher stabilities.However,QD emitting layers also have low mobilities,and thus the devices require large voltages for operation due to the presence of surface organic ligands.

Supersaturation controlled growth of MAFAPbI3 perovskite film for high efficiency solar cells

Controlling the nucleation and growth of organic-inorganic hybrids perovskite is of key importance to improve the morphology and crystallinity of perovskite films. However, the growth mechanism of perovskite films based on classical crystallization theory is not fully understood. Here, we develop a supersaturation controlled strategy(SCS) to balance the nucleation and crystal growth speeds. By this strategy, we are able to find an ideal supersaturation region to realize a balance of nucleation and crystal growth, which yields highly crystallized perovskite films with micrometer-scale grains. Besides, we provide a thoughtful analysis of nucleation and growth based on the fabrication of the perovskite films. As a result, the highest photovoltaic power conversion efficiencies(PCE) of 19.70% and 20.31% are obtained for the planar and the meso-superstructured devices, respectively. This strategy sheds some light for understanding the film growth mechanism of high quality perovskite film, and it provides a facile strategy to fabricate high efficiency perovskite solar cells.

Band alignment towards high-efficiency NiOx-based Sn-Pb mixed perovskite solar cells

Narrow-bandgap tin-lead(Sn-Pb)mixed perovskite solar cells(PSCs)play a key role in constructing perovskite tandem solar cells that are potential to overpass Shockley-Queisser limit.A robust,chemically stable and lowtemperature-processed hole transporting layer(HTL)is essential for building high-efficiency Sn-Pb solar cells and perovskite tandem solar cells.Here,we explore a roomtemperature-processed NiOx(L-NiOx)HTL based on nanocrystals(NCs)for Sn-Pb PSCs.In comparison with hightemperature-annealed NiOx(H-NiOx)film,the L-NiOx film shows deeper valence band and lower trap density,which increases the built-in potential and reduces carrier recombination,leading to a power conversion efficiency of 18.77%,the record for NiOx-based narrow-bandgap PSCs.Furthermore,the device maintains about 96%of its original efficiency after 50 days.This work provides a robust and room-temperatureprocessed HTL for highly efficient and stable narrow-bandgap PSCs.

In-situ growth of low-dimensional perovskite-based insular nanocrystals for highly efficient light emitting diodes

Regulation of perovskite growth plays a critical role in the development of high-performance optoelectronic devices.However,judicious control of the grain growth for perovskite light emitting diodes is elusive due to its multiple requirements in terms of morphology,composition,and defect.Herein,we demonstrate a supramolecular dynamic coordination strategy to regulate perovskite crystallization.The combined use of crown ether and sodium trifluoroacetate can coordinate with A site and B site cations in ABX_(3) perovskite,respectively.The formation of supramolecular structure retard perovskite nucleation,while the transformation of supramolecular intermediate structure enables the release of components for slow perovskite growth.This judicious control enables a segmented growth,inducing the growth of insular nanocrystal consist of low-dimensional structure.Light emitting diode based on this perovskite film eventually brings a peak external quantum efficiency up to 23.9%,ranking among the highest efficiency achieved.The homogeneous nano-island structure also enables high-efficiency large area(1 cm^(2))device up to 21.6%,and a record high value of 13.6%for highly semi-transparent ones.

Tin Halide Perovskite Solar Cells:An Emerging Thin-Film Photovoltaic Technology

Perovskite semiconductors are regarded as nextgeneration photovoltaic materials owing to their superb optoelectronic properties,including an excellent carrier diffusion length,strong light absorbption,low defect density,and solution processability.The PCE of lead perovskite solar cells(LPSC)rapidly increased from 3.8 to 25.5%in the past decade.However,the inclusion of soluble,toxic lead shadows its application due to environmental concerns.Furthermore,on the basis of the Shockley−Quisser(S−Q)limit,the efficiency of lead perovskite is limited to 32%since its band gap is>1.5 eV.To increase the efficiency of perovskite solar cells further,perovskite materials with a smaller band gap are required.Tin halide perovskite is currently the most promising alternative candidate that can address the above challenges due to its potentially less toxic character and electronic configuration analogous to that of lead.Its band gap(sub-1.4 eV)is lower than that of lead perovskite,approaching the ideal band gap with a theoretical efficiency of up to 33.4%based on the S−Q equation.However,tin perovskite is extremely easy to oxidize due to its unique electronic structure.Early works focus on the development of methods to reduce tin oxidation such as the addition of antioxidant additives or using low-dimensional structures.On the basis of these strategies,the reproducibility and efficiency of TPSCs have been significantly improved.In recent years,many works including composition engineering,functional additives,and device structure engineering have been used to improve the performance of TPSCs.On the basis of these strategies,the open-circuit voltage is improved to 0.94 V and the PCE certified by an independent laboratory is up to 12.4%.Meanwhile,the stability of TPSCs is significantly improved,and the stabilized power output time is up to 1000 h.Therefore,tin perovskite is emerging as a new generation of low-cost thin-film photovoltaic technology.This Account summarizes the properties of tin halide perovskites and the material and device engineering strategies toward more efficient and stable TPSCs.We highlight the unique properties of tin perovskites that distinguish them from lead perovskites,including their electronic structure,band structure,chemical properties,and so on.We discuss the critical challenges for the further development of TPSCs such as oxidation,high background carriers,uncontrollable crystallization,interface recombination,band alignment,and instability.In the end,we introduce potential directions for the future development of TPSCs including probing the formation mechanisms of tin perovskite,revealing the basic properties of Sn perovskite,overcoming the stability issue of TPSCs,and understanding TPSC device physics and structure engineering.

Emerging highly emissive and stable white emitting “phosphores” based on lead-free inorganic halide perovskites

Single materials generating high-efficiency white light emission are of particular interest for lighting. Recently, metal halide perovskite is emerging as a promising candidate for white light emission materials. However, lead halide perovskites showing broad spectrum light emission generally present low luminescence quantum yield and the emission spectrum deviates from the standard white light color coordinate.

High-member low-dimensional Sn-based perovskite solar cells

Sn-based perovskites are promising thin-film photovoltaic materials for their ideal bandgap and the eco-friendliness of Sn,but the performance of Sn-based perovskite solar cells is hindered by the short carrier diffusion length and large defect density in nominally-synthesized Sn-based perovskite films.Herein we demonstrate that a long carrier diffusion length is achievable in quasi-2D Sn-based perovskite films consisting of high-member low-dimensional Ruddlesden-Popper(RP)phases with a preferred crystal orientation distribution.The key to the film synthesis is the use of a molecular additive formed by phenylethylammonium cations and optimally mixed halide-pseudohalide anions,which favorably tailors the quasi-2D Sn-based perovskite crystallization kinetics.The high-member RP film structure effectively enhances device short-circuit current density,giving rise to an increased power conversion efficiency(PCE)of 14.6%.The resulting device demonstrates a near-unity shelf stability upon1,000 h in nitrogen.A high reproductivity is also achieved with a count of 50 devices showing PCEs within a narrow range from minimum 13.0%to maximum 14.6%.

Hole-transporting layer-free inverted planar mixed lead-tin perovskite-based solar cells

Mixed lead-tin （Pb-Sn） perovskites present a promising strategy to extend the light-harvesting range of perovskite-based solar cells （PSCs）. The use of electron- transporting layer or hole-transporting layer （HTL） is critical to achieve high device efficiency. This strategy, however, requires tedious layer-by-layer fabrication as well as high-temperature annealing for certain oxides. In this work, we fabricated HTL-free planar FAPb0.5Sn0.5I3 PSCs with the highest efficiency of 7.94%. High short- circuit current density of 23.13 mA/cm2 was attained, indicating effective charge extraction at the ITO/ FAPb0.5Sn0.5I3 interface. This finding provides an alter- native strategy to simplify the manufacture of single- junction or tandem PSCs.

Molecularly manipulating orientation of hole transporting layers and mitigation of electrical loss for dopant-free CsPbI_(2)Br solar cells

Organo-lead halide perovskites(OHPs) possess superior optoelectronic properties and have achieved an amazing certified power conversion efficiency(PCE) of 25.5% in perovskite solar cells(PSCs)[1]. Recent studies revealed that the organic cations such as methylammonium(MA^(+)) and formamidinium(FA^(+)) and anions with weak electronegativity such as I^(-) in OHPs were causing instability.

Planar core based starburst triphenylamine molecules as hole transporting materials for high-performance perovskite solar cells

Starburst triphenylamine molecules are generally used as hole transporting materials (HTMs)for optoelectronic devices like solar cells,light emitting diode and field effect transistors .The use of starburst triphenylamine molecules like spiro-OMeTAD HTM initiated the construction of solid state perovskite solar cells (PSCs).Currently,based on triphenylamine HTMs,the highest power conversion efficiency (PCE)of PSCs is up to 22.1%.