Structurally Flexible 2D Spacer for Suppressing the Electron-Phonon Coupling Induced Non-Radiative Decay in Perovskite Solar Cells

This study presents experimental evidence of the dependence of non-radiative recombination processes on the electron-phonon coupling of perovskite in perovskite solar cells(PSCs).Via A-site cation engineering,a weaker electron-phonon coupling in perovskite has been achieved by introducing the structurally soft cyclohexane methylamine(CMA^(+))cation,which could serve as a damper to alleviate the mechanical stress caused by lattice oscillations,compared to the rigid phenethyl methylamine(PEA^(+))analog.It demonstrates a significantly lower non-radiative recombination rate,even though the two types of bulky cations have similar chemical passivation effects on perovskite,which might be explained by the suppressed carrier capture process and improved lattice geometry relaxation.The resulting PSCs achieve an exceptional power conversion efficiency(PCE)of 25.5%with a record-high opencircuit voltage(V_(OC))of 1.20 V for narrow bandgap perovskite(FAPbI_(3)).The established correlations between electron-phonon coupling and non-radiative decay provide design and screening criteria for more effective passivators for highly efficient PSCs approaching the Shockley-Queisser limit.

Minimizing interfacial energy losses in inverted perovskite solar cells by a dipolar stereochemical 2D perovskite interface

Inverted perovskite solar cells(PSCs) have attracted broad research and industrial interest owing to their suppressed hysteresis,cost-effectiveness,and easy-fabrication.However,the issue of non-radiative recombination losses at the n-type interface between the perovskite and fullerene has impeded further improvement of photovoltaic performance.Here,we modify the n-type interface of FAPbI_(3) perovskite films by constructing a stereochemical two-dimensional(2D) perovskite interlayer,in which the organic cations comprise both pyridine and ammonium groups.The pyridine N donor can create stable bonding with the surface-uncoordinated Pb on the perovskite,thereby passivating the shallow-level defects and enhancing the air stability of the film.Furthermore,the pyridine N donor also offers a positive polar interface to decrease the surface work function of the perovskite film,enabling n-type modification.Ultimately,we employ a p-i-n photovoltaic(PV) device with the positive dipole interlayer at perovskite/fullerene contact and achieve remarkable photoelectric conversion efficiency(PCE) of 22.0%.

Achieving improved stability and minimal non-radiative recombination loss for over 18%binary organic photovoltaics via versatile interfacial regulation strategy

Interfacial regulation,serving multiple roles,is critical for the fabrication of stable and efficient organic photovoltaics(OPVs).Herein,a multifunctional cathode interlayer PDINO(15 nm)is prepared by regulating film thickness,which is inserted between active components and stable silver electrode to align work function,and maintain good interfacial contact and device stability.The thick film can help to reduce interfacial surface defects,keep stable surface morphology,and block the silver diffusion into the active layer.Consequently,the optimal PM6:Y6 device records an impressive power conversion efficiency(PCE)of 17.48%with minimized non-radiative recombination loss of 0.239 V.More importantly,the unencapsulated device maintains 91%of the original PCE after aging for over 60 days at 25℃ and 10%relative humidity in dark conditions.Meanwhile,the PM6:eC9 device achieves a remarkable PCE of 18.22%with the enhancement of open-circuit voltage(V_(oc)).Furthermore,the 1 cm^(2) device-based PDINO(15 nm)/Ag shows a high PCE of 15.2%while only 12.6%for PDINO(9 nm)/Al,indicating the good compatibility of PDINO(15 nm)interlayer with the R2R coating processes used in large-area OPVs fabrication.This work highlights the promise of interfacial regulation to simultaneously stabilize and enhance the efficiency of organic photovoltaics.

Surface passivation by multifunctional carbon dots toward highly efficient and stable inverted perovskite solar cells

Interfacial imperfections between the perovskite layer and the electron transport layer(ETL)in perovskite solar cells(PSCs)can lead to performance loss and negatively influence long-term operational stability.Here,we introduce an interface engineering method to modify the interface between perovskite and ETL by using multifunctional carbon dots(CDs).C=O in the CDs can chelate with the uncoordinated Pb2+in the perovskite material,inhibit interfacial recombination,and enhance the performance and stability of device.In addition,–OH in CDs forms hydrogen bonds with I-and organic cation in perovskite,inhibiting light-induced I2release and organic cation volatilization,causing irreversible degradation of perovskite films,thereby enhancing the long-term operational stability of PSCs.Consequently,we achieve the champion inverted device with an efficiency of 24.02%.The CDs-treated PSCs exhibit high operational stability,and the maximum power point tracking only attenuates by 12.5%after 1000 h.Interfacial modification engineering supported by multifunctional quantum dots can accelerate the road to stable PSCs.

PEROVSKITE SEMICONDUCTOR OPTOELECTRONIC DEVICES Rational molecular passivation for high-performance perovskite light-emitting diodes

Solution-processed metal halide perovskites (MHPs) have received significant interest for cost-effective, high-performance optoelectronic devices. In addition to the great successes in photovoltaics, their excellent luminescence and charge transport properties also make them promising for light emitting diodes (LEDs). To achieve high-efficiency perovskite LEDs (PeLEDs), extensive efforts have been carried out to enhance radiative recombination rates by confining the electrons and holes. In addition to enhancing radiative recombination rates, it is equally important to decrease the non-radiative recombination for improving the device performance. Passivation of the defects could be an efficient way for reducing the non-radiative recombination.

Reducing the voltage loss of Y-series acceptor based organic solar cells via ternary/quaternary strategies

In recent years, with the emergence of non-fullerene fused-ring acceptors, power conversion efficiencies (PCEs) of organic solar cells (OSCs) have exceeded 19%.However, compared to inorganic or perovskite photovoltaic cells, a higher voltage loss has become one of the key factors limiting further improvement in the PCEs of OSCs.The ternary/quaternary strategy has been identified as a feasible and effective way to obtain high-efficiency OSCs.In this review, a brief outline is given of the key roles that guest materials played in reducing voltage losses in solar cell devices and a brief look at the future material design and the design of ternary/quaternary systems.

How to get high-efficiency lead chalcogenide quantum dot solar cells?

Lead chalcogenide colloidal quantum dots(CQDs)are regarded as attractive absorption materials for novel solar cells(SCs).The cost of lead chalcogenide CQD has been decreased to a commercialization target of$5/g due to the direct production of CQD inks.However,the photoelectric conversion efficiency(PCE)of lead chalcogenide CQDSCs is presently close to 14%,well below the commercialization target(20%),which is only 41%of the theoretical Shockley-Queisser limit efficiency.In this study,the different losses of open-circuit voltage(V_(oc)),fill factor(FF),and short circuit current density(J_(sc))for current CQDSCs are systematically discussed,as well as the percentage and likely causes of each loss.Then the primary reasons for the CQDSCs’performance constraints are highlighted.Following that,we focus on the CQDSCs interfaces(i.e.,CQD/CQD,CQD/HTL,and ETL/CQD)and explore viable ways to reduce device performance loss.Finally,based on the discussion above,we propose many enhancements to significantly solve numerous major obstacles impeding device performance to boost the PCE of CQDSCs for future commercialization significantly.

Multifunctional anchoring of O-ligands for high-performance and stable inverted perovskite solar cells

Functional additives have recently been regarded as emerging candidates to improve the performance and stability of perovskite solar cells(PSCs).Herein,nicotinamide(N),2-chloronicotinamide(2Cl),and 6-chloronicotinamide(6Cl)were employed as O-ligands to facilitate the deposition of MAPbI_(3)(MA=methylammonium)and MA-free FA_(0.88)Cs_(0.12)PbI_(2.64)Br_(0.36)(FA=formamidinium)perovskite films by multifunctional anchoring.By density functional theory(DFT)calculations and ultraviolet photoelectron spectroscopy(UPS)measurements,it is identified that the highest occupied molecular orbital(HOMO)level for additive modified MAPbI_(3)perovskite could reduce the voltage deficit for hole extraction.Moreover,due to the most favorable charge distribution and significant improvements in charge mobility and defect passivation,the power conversion efficiency(PCE)of 2Cl-MAPbI_(3)PSCs was significantly improved from 19.32%to 21.12%.More importantly,the two-dimensional grazing-incidence wide-angle X-ray scattering(GIWAXS)analysis showed that PbI_(2) defects were effectively suppressed and femtosecond transient absorption(TA)spectroscopy demonstrated that the trap-assisted recombination at grain boundaries was effectively inhibited in the 2Cl-MA-free film.As a result,the thermally stable 2Cl-MA-free PSCs achieved a remarkable PCE of 23.13%with an open-circuit voltage(V_(oc))of 1.164 V and an ultrahigh fill factor(FF)of 85.7%.Our work offers a practical strategy for further commercializing stable and efficient PSCs.

有机半导体增强介电屏蔽效应以制备高效稳定的钙钛矿太阳能电池

在钙钛矿太阳能电池(pero-SCs)中,载流子扩散过程中带电缺陷的捕获是其非辐射复合损失的主要来源,而常见的缺陷态钝化策略具有较强的尺寸依赖性,使得大面积应用受限.因此,本文通过精准设计合成高介电常数的p-型有机半导体,构筑了具备高介电常数的钙钛矿薄膜,增强了介电屏蔽效应,降低了载流子捕获概率,减少了非辐射复合损失.该本征策略表现出较低的钙钛矿组分和尺寸依赖性,基于此策略制备了效率为23.35%的小面积(0.062 cm^(2))和21.93%的大面积(1 cm^(2))器件;同时,该策略提高了器件的工作稳定性和热稳定性,为制备高性能的大面积pero-SCs开辟了一条新途径.

Built-in electric field thickness design for betavoltaic batteries

Isotope source energy deposition along the thickness direction of a semiconductor is calculated,based upon which an ideal short current is evaluated for betavoltaic batteries.Electron-hole pair recombination and drifting length in a PN junction built-in electric field are extracted by comparing the measured short currents with the ideal short currents.A built-in electric field thickness design principle is proposed for betavoltaic batteries：after measuring the energy deposition depth and the carrier drift length,the shorter one should then be chosen as the built-in electric field thickness.If the energy deposition depth is much larger than the carrier drift length,a multi-junction is preferred in betavoltaic batteries and the number of the junctions should be the value of the deposition depth divided by the drift length.

Calculation studies on point defects in perovskite solar cells

The close-to-optimal band gap,large absorption coefficient,low manufacturing cost and rapid increase in power conversion efficiency make the organic-inorganic hybrid halide（CH3NH3PbI3）and related perovskite solar cells very promising for commercialization.The properties of point defects in the absorber layer semiconductors have important influence on the photovoltaic performance of solar cells,so the investigation on the defect properties in the perovskite semiconductors is necessary for the optimization of their photovoltaic performance.In this work,we give a brief review to the first-principles calculation studies on the defect properties in a series of perovskite semiconductors,including the organic-inorganic hybrid perovskites and inorganic halide perovskites.Experimental identification of these point defects and characterization of their properties are called for.

Highly regular rosette-shaped cathodoluminescence in GaN selfassembled nanodisks and nanorods

Self-assembled GaN nanorods were grown by metal-organic chemical vapor deposition.A highly regular rosette-shaped cathodoluminescence pattern in the GaN nanorods is observed,where its origin is helpful to deepen the understanding of GaN nanorod growth.The pattern forms at the very early stages of nanorod growth,which consists of yellow luminescence at the edges and the non-luminous region at six vertices of the hexagon.To clarify its origin,we carried out detailed cathodoluminescence studies,electron microscopy studies and nanoscale secondary ion mass spectrometry at both the nanorod surface and cross-section.We found the pattern is not related to optical resonance modes or polarity inversion,which are commonly reported in GaN nanostructures.After chemical composition and strain analysis,we found higher carbon and nitrogen cluster concentration and large compressive strain at the pattern area.The pattern formation may relate to facet preferential distribution of non-radiative recombination centers related to excess carbon/nitrogen.This work provides an insight into strain distribution and defect-related emission in GaN nanorod,which is critical for future optoelectronic applications.