Influence of charge transport layer on the crystallinity and charge extraction of pure tin-based halide perovskite film

As one of the most compelling photovoltaic devices, halide perovskite (PVK) solar cells have achieved a new surprising record power conversion efficiency (PCE) of 25.8%in 2021 [1]. This demonstrates the great potential of halide PVK solar cells as a highly competitive substitute to replace silicon-based solar cells in the photovoltaic market [2–6].

Chiral cation promoted interfacial charge extraction for efficient tin-based perovskite solar cells

Pb-free Sn-based perovskite solar cells(PSCs) have recently made inspiring progress, and power conversion efficiency(PCE) of 14.8% has been achieved. However, due to the energy-level mismatch and poor interfacial contact between commonly used hole transport layer(i.e., poly(3,4-ethylenedioxythio phene):poly(styrene sulfonate), PEDOT:PSS) and FASnI_(3) film, it is still challenging to effectively extract holes at the interface. Owing to the p-type nature of Sn-based perovskites, the efficient hole extraction is of particular significance to improve the PCE of their solar cells. In this work, for the first time, the role of chiral cations, a-methylbenzylamine(S-/R-/rac-MBA), in promoting hole transportation of FASnI_(3)-based PSCs is demonstrated. The introduction of MBAs is found to form 2D/3D film with lowdimensional structures locating at PEDOT:PSS/FASnI_(3) interface, which facilitates the energy level alignment and efficient charge transfer at the interface. Importantly, chiral-induced spin selectivity(CISS)effect of R-MBA_(2)SnI_(4)induced by chiral R-MBA cation is found to further assist the specific interfacial transport of accumulated holes. As a result, R-MBA-based PSCs achieve decent PCE of 10.73% with much suppressed hysteresis and enhanced device stability. This work opens up a new strategy to efficiently promote the interfacial extraction of accumulated charges in working PSCs.

Graphdiyne Oxide Modified NiO_(x) for Enhanced Charge Extraction in Inverted Planar MAPbI_(3) Perovskite Solar Cells

The interface defects and nickel vacancies of the NiO_(x)lead to interface charge recombination,which limits its application in perovskite solar cells.Here,graphdiyne oxide(GDYO)was added to NiO_(x)as an inorganic hole transporting material.It is found that the average carrier lifetime declined from 29.2 ns to 5.4 ns and the recombination resistance increased significantly after the GDYO adding determined by the time-resolved photoluminescence and electrochemical impedance spectroscopy analysis.We further demonstrated that the GDYO adding to NiO_(x)effectively improved the charge extraction,accelerated the charge transportation and suppressed the charge recombination.Consequently,the optimized NiO_(x)(GDYO)-based cell showed superior performance with a higher fill factor(81.99%)and improved stability with respect to the reference device.This method provides a new method for property regulation of NiO_(x)in inverted planar MAPbI_(3) perovskite solar cells.

Enhancing the stability of planar perovskite solar cells by green and inexpensive cellulose acetate butyrate

Although the efficiency of organic–inorganic hybrid halide perovskite solar cells has been improved rapidly, the intrinsic instability of perovskite materials restricts their commercial application. Here, an eco-friendly and low-cost organic polymer, cellulose acetate butyrate(CAB), was introduced to the grain boundaries and surfaces of perovskite, resulting in a high-quality and low-defect perovskite film with a nearly tenfold improvement in carrier lifetime. More importantly, the CAB-treated perovskite films have a well-matched energy level with the charge transport layers, thus suppressing carrier nonradiative recombination and carrier accumulation. As a result, the optimized CAB-based device achieved a champion efficiency of 21.5% compared to the control device(18.2%). Since the ester group in CAB bonds with Pb in perovskite, and the H and O in the hydroxyl group bond with the I and organic cations in perovskite,respectively, it will contribute to superior stability under heat, high humidity, and light soaking conditions. After aging under 35% humidity(relative humidity, RH) for 3300 h, the optimized device can still maintain more than 90% of the initial efficiency;it can also retain more than 90% of the initial efficiency after aging at 65 ℃, 65% RH, or light(AM 1.5G) for 500 h. This simple optimization strategy for perovskite stability could facilitate the commercial application of perovskite solar cells.

Progress in hole-transporting materials for perovskite solar cells

In recent years the photovoltaic community has witnessed the unprecedented development of perovskite solar cells（PSCs） as they have taken the lead in emergent photovoltaic technologies. The power conversion efficiency of this new class of solar cells has been increased to a point where they are beginning to compete with more established technologies. Although PSCs have evolved a variety of structures, the use of hole-transporting materials（HTMs） remains indispensable. Here, an overview of the various types of available HTMs is presented. This includes organic and inorganic HTMs and is presented alongside recent progress in associated aspects of PSCs, including device architectures and fabrication techniques to produce high-quality perovskite films. The structure, electrochemistry, and physical properties of a variety of HTMs are discussed, highlighting considerations for those designing new HTMs. Finally, an outlook is presented to provide more concrete direction for the development and optimization of HTMs for highefficiency PSCs.

Can the efficiencies of simplified perovskite solar cells go higher?

In recent years, metal halide perovskites have emerged as star semiconducting materials in the field of optoelectronic devices owing to their fascinating optoelectronic properties. Of particular interest are perovskite solar cells (PSCs), which have witnessed skyrocketing power conversion efficiencies (PCEs) within a short period of time, and were recently certified to reach 25.5%, which is already higher than other thin film photovoltaic technologies[1]. Nevertheless, multiple layers are still needed for state-of-theart PSCs to achieve high PCEs over 21%.

TiO_2 composite electron transport layers for planar perovskite solar cells by mixed spray pyrolysis with precursor solution incorporating TiO_2 nanoparticles

Perovskite solar cells with planar structure are attractive for their simplified device structure and reduced hysteresis effect. Compared to conventional mesoporous devices, TiO2 porous scaffold layers are removed in planar devices. Then, compact TiO2 electron transport layers take the functions of extracting electrons, transporting electrons, and blocking holes. Therefore, the properties of these compact TiO2 layers are important for the performance of solar cells. In this work, we develop a mixed spray pyrolysis method for producing compact TiO2 layers by incorporating TiO2 nanoparticles with dif- ferent size into the precursor solutions. For the optimized nanoparticle size of 60 nm, a power conversion efficiency of 16.7% is achieved, which is obviously higher than that of devices without incorporated nanoparticles （9.9%）. Further in- vestigation reveals that the incorporation of nanoparticles can remarkably improve the charge extraction and recombination processes.

Effects of the incorporation amounts of CdS and Cd(SCN_(2)H_(4))_(2)Cl_(2)on the performance of perovskite solar cells

An excellent organolead halide perovskite film is important for the good performance of perovskite solar cells(PSCs).However,defects in perovskite crystals can affect the photovoltaic properties and stability of solar cells.To solve this problem,this study incorporated a complex of Cd S and Cd(SCN_(2)H_(4))_(2)Cl_(2)into the CH_(3)NH_(3)Pb I_(3)active layer.The effects of different doping concentrations of Cd S and Cd(SCN_(2)H_(4))_(2)Cl_(2)on the performance and stability of PSCs were analyzed.Results showed that doping appropriate incorporation concentrations of Cd S and Cd(SCN_(2)H_(4))_(2)Cl_(2)in CH_(3)NH_(3)Pb I_(3)can improve the performance of the prepared solar cells.In specific,Cd S and Cd(SCN_(2)H_(4))_(2)Cl_(2)can effectively passivate the defects in perovskite crystals,thereby suppressing the charge recombination in PSCs and promoting the charge extraction at the TiO_(2)/perovskite interface.Due to the reduction of perovskite crystal defects and the enhancement of compactness of the Cd S:Cd(SCN_(2)H4)_(2)Cl_(2):CH_(3)NH_(3)Pb I_(3)composite film,the stability of PSCs is significantly improved.

Non-Halogenated Solvent-Processed High-Efficiency Polymer Solar Cells:the Role of Diphenyl Ether in Morphology,Light-Trapping,Transport Properties

There is an urgent need to use green non-halogenated solvents to prepare polymer solar cells(PSCs) for industrialization.It is time-consuming but necessary to find a suitable non-halogenated solvent/additive combination for a given donor:acceptor materials system.In this research,we report a non-halogenated binary solvent system toluene/diphenyl ether(DPE) for the PBDTT-DTffBT:PC_(71)BM and PM6:Y6 blending systems that exhibit comparable power conversion efficiency(PCE) to that of devices prepared with halogenated solvents.The nano scale morphology indicates that blending film processed solely with toluene has poor phase segregation and a rough surface,which hinders charge separation and interfacial contact.Besides,the total absorption spectra revealed significant light-trapping losses in the toluene-processed solar cells,resulting in low photocurrent generation.DPE incorporation addresses these issues and significantly improves the short-circuit current density and fill factor.Moreover,non-halogen solvent-processed devices exhibit high hole mobility and low transporting impedance properties.The present study enriches the families of eco-friendly,high-efficiency PSCs fabricated using nonhalogenated solvents.

Performance of beam-type piezoelectric vibration energy harvester based on ZnO film fabrication and improved energy harvesting circuit

We demonstrate a piezoelectric vibration energy harvester with the ZnO piezoelectric film and an improved synchronous electric charge extraction energy harvesting circuit on the basis of the beam-type mechanical structure,especially investigate its output performance in vibration harvesting and ability to generate charges.By establishing the theoretical model for each of vibration and circuit,the numerical results of voltage and power output are obtained.By fabricating the prototype of this harvester,the quality of the sputtered film is explored.Theoretical and experimental analyses are conducted in open-circuit and closed-circuit conditions,where the open-circuit mode refers to the voltage output in relation to the ZnO film and external excitation,and the power output of the closed-circuit mode is relevant to resistance.Experimental findings show good agreement with the theoretical ones,in the output tendency.It is observed that the properties of ZnO film achieve regularly direct proportion to output performance under different excitations.Furthermore,a maximum experimental power output of 4.5 mW in a resistance range of 3 kΩ-8 kΩis achieved by using an improved synchronous electric charge extraction circuit.The result is not only more than three times the power output of classic circuit,but also can broaden the resistance to a large range of 5 kΩunder an identical maximum value of power output.In this study we demonstrate the fundamental mechanism of piezoelectric materials under multiple conditions and take an example to show the methods of fabricating and testing the ZnO film.Furthermore,it may contribute to a novel energy harvesting circuit with high output performance.

Graphene oxide as a hole extraction layer loaded on BiVO_(4)photoanode for highly efficient photoelectrochemical water splitting

The tailor-made oxygen evolution catalysts(OECs)paired with photoanodes offer a path to promote water oxidation kinetics;however,the unsatisfied interface between OECs and photoanode sets a barrier for efficient charge transfer.Herein,a graphene oxide(GO)layer to promote the charge transfer from BiVO_(4)(BVO)to NiOOH OEC is reported.It is found that GO layer inserted between BVO and NiOOH can not only serve as hole extraction layer due to its hole storage capability,but also improve the stability.Finally,the rationally designed NiOOH/GO/BVO photoanode achieves a photocurrent density of 3.81 mA·cm^(-2)at 1.23 V(vs.reversible hydrogen electrode(RHE)),which is 3.85 times as high as that of bare BVO.This work opens up low-cost auxiliary materials for enhancing photoelectrochemical water splitting.

Thick Active-Layer Organic Solar Cells

Organic solar cells(OSCs)present a promising renewable energy technology due to their cost-effectiveness,adaptability,and lightweight nature.The advent of non-fullerene acceptors has further boosted their significance,allowing for power conversion efficiencies surpassing 19%even with an active layer thickness of about 100 nm.However,in order to achieve large scale production,it is necessary to fabricate OSCs with thicker active layers exceeding 300 nm that are compatible with large-area printing techniques.Nevertheless,OSCs with thick active layers have inferior performance compared to those with thin active layers.To expedite the transition of OSCs from laboratory to industrial high-throughput manufacturing,considerable efforts have been made to comprehend the performance limitations of thick active-layer OSCs,develop novel photoactive materials that are high-performance and tolerant towards the thickness of the active layer,and optimize the morphology of the photoactive layer and device structure.This review aims to provide a comprehensive summary of the mechanisms that lead to efficiency loss in thick active-layer OSCs,the representative works on molecular design,and the optimization strategies for high-performance thick active-layer OSCs,and the remaining challenges that must be addressed.

Surface states in TiO2 submicrosphere films and their effect on electron transport

Owing to their special three-dimensional network structure and high specific surface area,TiO2 submicrospheres have been widely used as electron conductors in photoanodes for solar cells.In recent years,utilization of TiO2 submicrospheres in solar cells has greatly boosted the photovoltaic performance.Inevitably,however,numerous surface states in the TiO2 network affect electron transport.In this work,the surface states in TiO2 submicrospheres were thoroughly investigated by charge extraction methods,and the results were confirmed by the cyclic voltammetry method.The results showed that ammonia can effectively reduce the number of surface states in TiO2 submicrospheres.Furthermore,in-depth characterizations indicate that ammonia shifts the conduction band toward a more positive potential and improves the interfacial charge transfer.Moreover,charge recombination is effectively prevented.Overall,the cell performance is essentially dependent on the effect of the surface states,which affects the electron transfer and recombination process.

Healing the degradable organic–inorganic heterointerface for highly efficient and stable organic solar cells

The heterointerface between the contacted organic and inorganic semiconductors critically affects the charge extraction,hence overall performance of organic optoelectronics,especially for organic solar cells(OSCs).Herein,we develop an effective interfacial strategy that simultaneously boosts the chemical,electric,and electronic properties of the organic–inorganic heterointerface of the derived OSCs,through implanting conjugated molecules as selfassemble monolayers(SAMs)to metal oxide nanoparticles(MO NPs).As results,SAM passivated zinc oxide nanoparticles(ZnO NPs)as electron transport layers(ETLs)not only enable the best performed OSCs containing MO ETLs,but also exhibit the most desirable thickness insensitive features(up to 300 nm).In addition,SAM-ZnO ETLs help also substantially improving the photostability of the derived OSCs.Overall,this work can be beneficial to the further development of high-performance and cost-effective OSCs.