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...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.展开更多
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...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%.展开更多
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 ...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.展开更多
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 ...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.展开更多
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 l...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.展开更多
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...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.展开更多
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...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.展开更多
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-chloronicotinamid...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.展开更多
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 drift...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.展开更多
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 ce...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.展开更多
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 u...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.展开更多
基金supported by the National Natural Science Foundation of China(U21A20331,81903743,22005322,22279151,and 22275004)National Science Fund for Distinguished Young Scholars(21925506).
文摘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.
基金financially supported by the National Ten Thousand Talent Program for Young Top-notch Talent,China,the National Natural Science Fund for Excellent Young Scholars,China(52022030)the National Natural Science Foundation of China,China(51972111,52203330)+7 种基金the Shanghai Pilot Program for Basic Research,China(22TQ1400100-5)the “Dawn”Program of Shanghai Education Commission,China(22SG28)the Shanghai Municipal Natural Science Foundation,China(22ZR1418000)the Science and Technology Innovation Plan of Shanghai Science and Technology Commission,China(22YF1410000)the Postdoctoral Research Foundation of China,China(2021M701190)the Fundamental Research Funds for the Central Universities,China(JKD01231632,JKVD1231041)the Major Science and Technology Projects of Inner Mongolia Autonomous Region,China(2021ZD0042)the Shanghai Engineering Research Center of Hierarchical Nanomaterials,China(18DZ2252400)。
文摘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%.
基金supported by the National Natural Science Foundation of China(51903189,51800334)。
文摘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.
基金supported by the National Natural Science Foundation of China(52172237,22261142666)the Shaanxi International Cooperation Project(2020KWZ-018)+3 种基金the Shaanxi Science Fund for Distinguished Young Scholars(2022JC-21)the Research Fund of the State Key Laboratory of Solidification Processing(NPU),China(2021-QZ-02)the Fundamental Research Funds for the Central Universities(D5000220033)the Hong Kong Scholars Program(XJ2022025)。
文摘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.
文摘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.
基金acknowledge the financial supports from the Department of Science and Technology of Inner Mongolia(No.2020GG0192)the Natural Science Foundation of Inner Mongolia(No.2022ZD04)+1 种基金the Inner Mongolia Normal University(No.112/1004031962)the Inner Mongolia Autonomous Region Postgraduate Research Innovation Fund(No.S20210274Z).
文摘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.
基金supported by the Japan Science and Technology Agency(JST)Mirai program(JPMJMI17EA)MEXT KAKENHI(Grant Nos.26286013,and 17H02736)。
文摘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.
基金This work was financially supported by the National Natural Science Foundation of China(51702038,U21A20331,51773212 and 81903743)the Sichuan Science&Technology Program(2020YFG0061)+1 种基金National Science Fund for Distinguished Young Scholars(21925506)Natural Science Foundation of Ningbo(2021J192).
文摘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.
基金supported by the National Key Research and Development Program of China(2020YFB1506400)the National Natural Science Foundation of China(51922074,22075194,and 51820105003)+3 种基金the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(20KJA430010)the Tang Scholarthe Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)the Collaborative Innovation Center of Suzhou Nano Science and Technology。
基金Project supported by the National Natural Science Foundation of China(Nos.90923039,51025521)the 111 Project of China(No. B08043)
文摘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.
基金Project supported by the National Natural Science Foundation of China(No.61574059)the Shanghai Rising-Star Program(No.14QA1401500)+1 种基金the Shu-Guang Program(15SG20)the CC of ECNU
文摘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.
基金B.J.Z.would like to thank the China Scholarship Council and the Australia National University for her scholarship supportX.Y.thanks the National Natural Science Foundation of China(Nos.61974166 and 51702368)for financial supportWe would like to thank Dr.Xu Zhang from Zhengzhou University for helpful discussion on some of the strain aspects in this work.
文摘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.