射频磁控溅射ZnO薄膜的光致发光

用射频磁控溅射法在硅衬底上沉积出具有良好的择优取向的多晶ZnO薄膜.在室温下进行光致发光测量,观察到明显的紫光发射(波长为402nm)和弱的紫外光发射 (波长为384nm).紫光发射源于氧空位浅施主能级到价带顶的电子跃迁;紫外光发射则源于导带与价带之间的电子跃迁.随着光激发强度的增加,紫光发射强度超线性增强,且稍有蓝移,而紫外光发光强度则近似线性增加.在氧气中高温退火后,薄膜结晶质量明显提高,紫光发射强度变弱,紫外光发射相对增强.     

射频磁控溅射ZnO薄膜的光致发光

用射频磁控溅射法在硅衬底上沉积出具有良好的择优取向的多晶ZnO薄膜.在室温下进行光致发光测量,观察到明显的紫光发射(波长为402nm)和弱的紫外光发射 (波长为384nm).紫光发射源于氧空位浅施主能级到价带顶的电子跃迁;紫外光发射则源于导带与价带之间的电子跃迁.随着光激发强度的增加,紫光发射强度超线性增强,且稍有蓝移,而紫外光发光强度则近似线性增加.在氧气中高温退火后,薄膜结晶质量明显提高,紫光发射强度变弱,紫外光发射相对增强.     

P型CuInSe_2薄膜的瞬态光电导

在低温下观察到P型CuInSe_2薄膜的瞬态光电导现象,并进行了理论和实验研究。认为该现象是由陷阱引起的光电导衰减使陷阱位垒妨碍光生电子和空穴的复合,通过隧道效应实现了光生电子和空穴的复合。理论与实验结果一致。     

射频磁控溅射ZnO薄膜的光致发光

用射频磁控溅射法在硅衬底上沉积出具有良好的择优取向的多晶 Zn O薄膜 .在室温下进行光致发光测量 ,观察到明显的紫光发射 (波长为 4 0 2 nm )和弱的紫外光发射 (波长为 384 nm ) .紫光发射源于氧空位浅施主能级到价带顶的电子跃迁 ;紫外光发射则源于导带与价带之间的电子跃迁 .随着光激发强度的增加 ,紫光发射强度超线性增强 ,且稍有蓝移 ,而紫外光发光强度则近似线性增加 .在氧气中高温退火后 ,薄膜结晶质量明显提高 ,紫光发射强度变弱 ,紫外光发射相对增强 .     

Ar~+轰击SrTiO_3表面的持续光电导现象

持续光电导现象在光电器件中有着潜在的应用。采用亚禁带光激发手段研究了SrTiO_3表面的持续光电导效应。Ar+轰击后的SrTiO_3单晶可以形成具有光电效应的表面导电层。在温度80 K至300 K范围内,饱和光电导与激光功率强度之间呈现幂律规律,表现出带间陷阱复合的特征。激光辐照中止后,持续光电导的衰减时间达到1000 s以上。光电流的衰减符合扩展指数律,弥散参数β维持在0.2左右,基本不随温度改变,而特征时间τ随温度升高从49.6 s增加到2706 s;在低温区(80~150 K)的载流子复合势垒是7.1 meV,而在室温附近(150~300K)的载流子复合势垒增加到95 meV。这些特征表明Ar~+轰击SrTiO_3表面的光电导在衰减过程符合随机局部势能涨落模型,在低温时由浅能级陷阱的复合占主导,而在室温时则由深能级陷阱的复合占主导。     

半导体多晶薄膜的瞬态光电导

在低温下观察到半导体多晶薄膜的瞬态光电导现象．给出了三维理论模型．理论研究表明，陷阶引起光电导，光生载流子通过隧道效应实现复合，使光电导逐渐衰减．我们的实验结果与理论计算结果符合得相当好．     

国外负电子亲和势光电阴极发展概况

一般光电阴极其真空能级在导带底之上,电子亲和势(或亲和力)为正,电子必须克服势垒才能逸出;而Ⅲ—Ⅴ族光电阴极和硅光电阴极其真空能级在导带底之下,电子亲和势为负,被光激发到导带的电子到达表面后,没有克服势垒的问题,能有更多的电     

入射光强对Ag-BaO薄膜内场助光电发射特性的影响

通过对不同光强入射下Ag-BaO薄膜内场助光电发射特性的测试,实验发现Ag BaO薄膜内场助光电发射电流随内场助偏压的增长过程经历了快速增长和缓慢增加两个阶段,相应的转折电压大小与入射光强有关.理论分析表明,内场助作用下Ag-BaO薄膜体内能带结构发生了Ag微粒和BaO介质间等效界面势垒减小及薄膜表面真空能级相对下降等两个方面的变化,其在内场助作用过程中相对效果的不同导致了光电流增长过程中的两个阶段;转折电压对入射光强的依赖关系源于光生载流子改变了薄膜体内的有效电场强度.     

N掺杂p型MgZnO薄膜的制备与性能研究

利用磁控溅射设备,Mg0.04Zn0.96O陶瓷靶材,以高纯的氮气与氩气混合气体作为溅射气体,在石英衬底上沉积获得了N掺杂p型Mg0.07Zn0.93O薄膜,薄膜的电阻率为21.47Ω·cm,载流子浓度为8.38×1016 cm-3,迁移率为3.45cm2/(V·s)。研究了该薄膜的结构与光学性能。实验结果显示,其拉曼光谱中出现了位于272和642cm-1左右与NO相关的振动模。低温光致发光光谱中,可以观察到位于3.201,3.384和3.469eV的3个发光峰,其中位于3.384eV的发光峰归因为导带电子到缺陷能级的复合发光,而位于3.469eV的发光峰归因为受主束缚激子(A0X)的辐射复合,这说明该N掺杂MgZnO薄膜的空穴载流子主要来自NO受主的贡献。     

晶体中光电子涨落的影响因素

针对晶体中光电子涨落的特点,分析了光吸收激发和热激发中影响光电子产生的因素.在光电子的衰减阶段,不同的电子陷阱所起的作用不同,浅电子陷阱由于延长了光电子在导带的弛豫时间,使光电子的衰减变缓;而深电子陷阱由于对光电子形成强束缚或作为复合中心加速了光电子的衰减.     

Near‐Infrared Photoresponse of One‐Sided Abrupt MAPbI3/TiO2 Heterojunction through a Tunneling Process

Trap states in semiconductors usually degrade charge separation and collection in photovoltaics due to trap‐mediated nonradiative recombination. Here, it is found that perovskite can be heavily doped in low concentration with non‐ignorable broadband infrared absorption in thick films and their trap states accumulate electrons through infrared excitation and hot carrier cooling. A hybrid one‐sided abrupt perovskite/TiO₂ p‐N heterojunction is demonstrated that enables partial collection of these trap‐filled charges through a tunneling process instead of detrimental recombination. The tunneling is from broadband trap states in the wide depleted p‐type perovskite, across the barrier of the narrow depleted TiO₂ region (<5 nm), to the N‐type TiO₂ electrode. The trap states inject carriers into TiO₂ through tunneling and produce around‐unity peak external quantum efficiency, giving rise to near‐infrared photovoltaics. The near‐infrared response allows photodetecting devices to work in both diode and conductor modes. This work opens a new avenue to explore the near‐infrared application of hybrid perovskites.     

Band‐Tail Recombination in Hybrid Lead Iodide Perovskite

Traps limit the photovoltaic efficiency and affect the charge transport of optoelectronic devices based on hybrid lead halide perovskites. Understanding the nature and energy scale of these trap states is therefore crucial for the development and optimization of solar cell and laser technology based on these materials. Here, the low‐temperature photoluminescence of formamidinium lead triiodide (HC(NH₂)₂PbI₃) is investigated. A power‐law time dependence in the emission intensity and an additional low‐energy emission peak that exhibits an anomalous relative Stokes shift are observed. Using a rate‐equation model and a Monte Carlo simulation, it is revealed that both phenomena arise from an exponential trap‐density tail with characteristic energy scale of ≈3 meV. Charge‐carrier recombination from sites deep within the tail is found to cause emission with energy downshifted by up to several tens of meV. Hence, such phenomena may in part be responsible for open‐circuit voltage losses commonly observed in these materials. In this high‐quality hybrid perovskite, trap states thus predominantly comprise a continuum of energetic levels (associated with disorder) rather than discrete trap energy levels (associated, e.g., with elemental vacancies). Hybrid perovskites may therefore be viewed as classic semiconductors whose band‐structure picture is moderated by a modest degree of energetic disorder.     

Boosting Photovoltaic Performance for Lead Halide Perovskites Solar Cells with BF4− Anion Substitutions

Composition engineering is a particularly simple and effective approach especially using mixed cations and halide anions to optimize the morphology, crystallinity, and light absorption of perovskite films. However, there are very few reports on the use of anion substitutions to develop uniform and highly crystalline perovskite films with large grain size and reduced defects. Here, the first report of employing tetrafluoroborate (BF₄^?) anion substitutions to improve the properties of (FA = formamidinium, MA = methylammonium (FAPbI₃)_0.83(MAPbBr₃)_0.17) perovskite films is demonstrated. The BF₄^? can be successfully incorporated into a mixed‐ion perovskite crystal frame, leading to lattice relaxation and a longer photoluminescence lifetime, higher recombination resistance, and 1–2 orders magnitude lower trap density in prepared perovskite films and derived solar cells. These advantages benefit the performance of perovskite solar cells (PVSCs), resulting in an improved power conversion efficiency (PCE) of 20.16% from 17.55% due to enhanced open‐circuit voltage (V_OC) and fill factor. This is the highest PCE for BF₄^? anion substituted lead halide PVSCs reported to date. This work provides insight for further exploration of anion substitutions in perovskites to enhance the performance of PVSCs and other optoelectronic devices.     

Grain Boundary and Interface Passivation with Core–Shell Au@CdS Nanospheres for High‐Efficiency Perovskite Solar Cells

The plasmonic characteristic of core–shell nanomaterials can effectively improve exciton‐generation/dissociation and carrier‐transfer/collection. In this work, a new strategy based on core–shell Au@CdS nanospheres is introduced to passivate perovskite grain boundaries (GBs) and the perovskite/hole transport layer interface via an antisolvent process. These core–shell Au@CdS nanoparticles can trigger heterogeneous nucleation of the perovskite precursor for high‐quality perovskite films through the formation of the intermediate Au@CdS–PbI₂ adduct, which can lower the valence band maximum of the 2,2,7,7‐tetrakis(N,N‐di‐p‐methoxyphenyl‐amine)9,9‐spirobifluorene (Spiro‐OMeTAD) for a more favorable energy alignment with the perovskite material. With the help of the localized surface plasmon resonance effect of Au@CdS, holes can easily overcome the barrier at the perovskite/Spiro‐OMeTAD interface (or GBs) through the bridge of the intermediate Au@CdS–PbI₂, avoiding the carrier accumulation, and suppress the carrier trap recombination at the Spiro‐OMeTAD/perovskite interface. Consequently, the Au@CdS‐based perovskite solar cell device achieves a high efficiency of over 21%, with excellent stability of ≈90% retention of initial power conversion efficiencies after 45 days storage in dry air.     

Energy level of minority carrier trap centers induced by light illumination in B-doped Cz-Si solar cells

The conversion efficiency of boron (B)-doped Czochralski silicon (Cz-Si) solar cells decreased by light illumination or minority carrier injection. Defects are induced by illumination and they act as trap centers, shorten the minority carrier (electron) lifetime. The energy level of this minority carrier trap center was determined by analyzing the open-circuit voltage (V_OC) changes as a function of substrate temperature. When substrate temperature is low, all electrons which are captured by the trap centers recombine with holes and they do not contribute to the generation of electric power. However, as the substrate temperature is increasing, some of the captured electrons are thermally excited to the conduction band before recombination. Hence, the lifetime of minority carriers are improved and V_OC is recovered. Based on this result, the energy level of trap center induced by light illumination is estimated to be 0.26 eV, which corresponds to the boron–oxygen-related defect (E_C-0.26 eV).     

Elucidating the Origins of Subgap Tail States and Open‐Circuit Voltage in Methylammonium Lead Triiodide Perovskite Solar Cells

Recombination via subgap trap states is considered a limiting factor in the development of organometal halide perovskite solar cells. Here, the impact of active layer crystallinity on the accumulated charge and open‐circuit voltage (V_oc) in solar cells based on methylammonium lead triiodide (CH₃NH₃PbI₃, MAPI) is demonstrated. It is shown that MAPI crystallinity can be systematically tailored by modulating the stoichiometry of the precursor mix, where small quantities of excess methylammonium iodide (MAI) improve crystallinity, increasing device V_oc by ≈200 mV. Using in situ differential charging and transient photovoltage measurements, charge density and charge carrier recombination lifetime are determined under operational conditions. Increased V_oc is correlated to improved active layer crystallinity and a reduction in the density of trap states in MAPI. Photoluminescence spectroscopy shows that an increase in trap state density correlates with faster carrier trapping and more nonradiative recombination pathways. Fundamental insights into the origin of V_oc in perovskite photovoltaics are provided and it is demonstrated why highly crystalline perovskite films are paramount for high‐performance devices.     

High Quality Perovskite Crystals for Efficient Film Photodetectors Induced by Hydrolytic Insulating Oxide Substrates

A high quality perovskite film is a key factor in determining the device performance, such as photovoltaic cells, light‐emission diodes, lasers, and photodetectors. Here, a method is presented to improve the crystalline quality of perovskite films on surface‐oxygen‐rich insulating oxide substrates, which can promote the growth of both the polycrystalline and single crystals and enhance the adhesion between the perovskites and the substrates. A much longer carrier diffusion length of exceeding 5 µm together with significantly reduced trap density and nonradiative recombination is achieved for the film. These perovskite films show much better lasing and photodetector performance, indicating promising applications for the light emitting, lasing, and detector devices.     

Photoconductivity and luminescence of CuInSe2 single crystals at a high level of optical excitation

The luminance-current and spectral characteristics of photoluminescence of the CuInSe₂ single crystals are studied. The superlinear portion of the excitation-intensity dependence of photoconductivity at low excitation intensities in compensated p-CuInSe₂ crystals is explained on the basis of a recombination model. The emission band that peaked at 0.98 eV in the n-CuInSe₂ photoluminescence spectrum corresponds to radiative recombination of electrons at the donor level with a depth of 0.04 eV. The maximum in the band intensity corresponds to the energy gap between the trap level and the valence band.     

Trapping and recombination processes via deep level T3 in semi-insulating gallium arsenide

Trapping and recombination of free carriers by deep level T₃ has been studied. Occupancy of the level by electrons and dynamics of its filling and emptying as a function of illumination with monoenergetic photons in 0.69–1.55 eV range has been monitored by the thermally stimulated currents method. We have found that level T₃ behaves more like a recombination center than like an ordinary electron trap. Besides trapping free electrons from conduction band, this trap can also communicate with valence band, trapping holes. The capture cross section for trapping a hole is estimated to be comparable or even larger than the capture cross section for trapping an electron. However, in many experimental conditions free electrons are generated more abundantly than free holes, and free carrier mobility and thermal velocity are both much higher for electrons than for holes. Therefore, electron trapping often prevails, so that this frequently detected defect, has been up to now most often perceived as a deep electron trap.     

Trapping and luminescence mechanisms in manganese-doped zinc silicate phosphorsa tunneling model

We have investigated electron trapping and luminescence (phosphorescence, thermoluminescence and photostimulated luminescence) mechanisms in Mn and Mn+As doped Zn₂SiO₄ phosphors. The intensities of both the phosphorescence and photostimulated luminescence are found to decay with time approximately as (time)^-1. The generally accepted model of such a decay of phosphorescence, based on thermal release of electrons from a broad distribution of trap energy levels, cannot explain the observed decay of the photostimulated luminescence. In order to explain both results we have developed a new model based on radiative recombination by tunneling between holes trapped on Mn ions and electrons in shallow traps or in excited states of the deeper traps. We derive a simple expression which describes for both experiments at all times the decay of the light intensity and its dependence on experimental conditions. The agreement between theory and experiment is found to be excellent.