Improving the UV-light stability of silicon heterojunction solar cells through plasmon-enhanced luminescence downshifting of YVO_(4):Eu^(3+),Bi^(3+)nanophosphors decorated with Ag nanoparticles

The ultraviolet(UV)light stability of silicon heterojunction(SHJ)solar cells should be addressed before large-scale production and applications.Introducing downshifting(DS)nanophosphors on top of solar cells that can convert UV light to visible light may reduce UV-induced degradation(UVID)without sacrificing the power conversion efficiency(PCE).Herein,a novel composite DS nanomaterial composed of YVO_(4):Eu^(3+),Bi^(3+)nanoparticles(NPs)and AgNPs was synthesized and introduced onto the incident light side of industrial SHJ solar cells to achieve UV shielding.The YVO_(4):Eu^(3+),Bi^(3+)NPs and Ag NPs were synthesized via a sol-gel method and a wet chemical reduction method,respectively.Then,a composite structure of the YVO_(4):Eu^(3+),Bi^(3+)NPs decorated with Ag NPs was synthesized by an ultrasonic method.The emission intensities of the YVO_(4):Eu^(3+),Bi^(3+)nanophosphors were significantly enhanced upon decoration with an appropriate amount of~20 nm Ag NPs due to the localized surface plasmon resonance(LSPR)effect.Upon the introduction of LSPR-enhanced downshifting,the SHJ solar cells exhibited an~0.54%relative decrease in PCE degradation under UV irradiation with a cumulative dose of 45 k W h compared to their counterparts,suggesting excellent potential for application in UV-light stability enhancement of solar cells or modules.

Sub-stochiometric MoO_(x) by radio-frequency magnetron sputtering as hole-selective passivating contacts for silicon heterojunction solar cells

The silicon heterojunction(SHJ)solar cell has long been considered as one of the most promising candidates for the next-generation PV market.Transition metal oxides(TMOs)show good carrier selectivity when combined with c-Si solar cells.This has led to the rapid demonstration of the remarkable potential of TMOs(especially MoO_(x))with high work function to replace the p-type a-Si:H emitting layer.MoO_(x) can induce a strong inversion layer on the interface of n-type c-Si,which is beneficial to the extraction and conduction of holes.In this paper,the radio-frequency(RF)magnetron sputtering is used to deposit MoO_(x) films.The optical,electrical and structural properties of MoO_(x) films are measured and analyzed,with focus on the inherent compositions and work function.Then the MoO_(x) films are applied into SHJ solar cells.When the MoO_(x) works as a buffer layer between ITO/p-a-Si:H interface in the reference SHJ solar cell,a conversion efficiency of 19.1%can be obtained.When the MoOx is used as a hole transport layer(HTL),the device indicates a desirable conversion efficiency of 17.5%.To the best of our knowledge,this current efficiency is the highest one for the MoO_(x) film as HTL by RF sputtering.

Influence of the initial transient state of plasma and hydrogen pre-treatment on the interface properties of a silicon heterojunction fabricated by PECVD

Amorphous/crystalline silicon heterojunctions（a-Si：H/c-Si SHJ） were prepared by plasma-enhanced chemical vapor deposition（PECVD）.The influence of the initial transient state of the plasma and the hydrogen pre-treatment on the interfacial properties of the heteroj unctions was studied.Experimental results indicate that： （1） The instability of plasma in the initial stage will damage the surface of c-Si.Using a shutter to shield the substrate for 100 s from the starting discharge can prevent the influence of the instable plasma process on the Si surface and also the interface between a-Si and c-Si.（2） The effect of hydrogen pre-treatment on interfacial passivation is constrained by the extent of hydrogen plasma bombardment and the optimal time for hydrogen pre-treatment is about 60 s.

Structural feature and electronic property of an (8, 0) carbon-silicon carbide nanotube heterojunction

A supercell of a nanotube heterojunction formed by an （8, 0） carbon nanotube （CNT） and an （8, 0） silicon carbide nanotube （SiCNT） is established, in which 96 C atoms and 32 Si atoms are included. The geometry optimization and the electronic property of the heterojunction are implemented through the first-principles calculation based on the density functional theory （DFT）. The results indicate that the structural rearrangement takes place mainly on the interface and the energy gap of the heterojunction is 0.31 eV, which is narrower than those of the isolated CNT and the isolated SiCNT. By using the average bond energy method, the valence band offset and the conduction band offset are obtained as 0.71 and -0.03 eV, respectively.

Laser-Induced Single Event Transients in Local Oxidation of Silicon and Deep Trench Isolation Silicon-Germanium Heterojunction Bipolar Transistors

We present a study on the single event transient （SET） induced by a pulsed laser in different silicon-germanium （SiGe） heterojunction bipolar transistors （HBTs） with the structure of local oxidation of silicon （LOCOS） and deep trench isolation （DTI）. The experimental results are discussed in detail and it is demonstrated that a SiGe HBT with the structure of LOCOS is more sensitive than the DTI SiGe HBT in the SET. Because of the limitation of the DTI structure, the charge collection of diffusion in the DTI SiGe HBT is less than that of the LOCOS SiGe HBT. The SET sensitive area of the LOCOS SiGe HBT is located in the eollector-substrate （C/S） junction, while the sensitive area of the DTI SiGe HBT is located near to the collector electrodes.

Effect of emitter layer doping concentration on the performance of a silicon thin film heterojunction solar cell

A novel type of n/i/i/p heterojunction solar cell with a-Si：H（15 nm）/a-Si：H（10 nm）/epitaxial c-Si（47 p.m）/epitaxial c-Si（3 um） structure is fabricated by using the layer transfer technique, and the emitter layer is deposited by hot wire chemical vapour deposition. The effect of the doping concentration of the emitter layer Sd （Sd=PH3/（PH3 ＋SiH4＋H2）） on the performance of the solar cell is studied by means of current density-voltage and external quantum efficiency. The results show that the conversion efficiency of the solar cell first increases to a maximum value and then decreases with Sd increasing from 0.1% to 0.4%. The best performance of the solar cell is obtained at Sd = 0.2% with an open circuit voltage of 534 mV, a short circuit current density of 23.35 mA/cm2, a fill factor of 63.3%, and a conversion efficiency of 7.9%.

Sensitivity investigation of 100-MeV proton irradiation to SiGe HBT single event effect

The single event effect(SEE) sensitivity of silicon–germanium heterojunction bipolar transistor(Si Ge HBT) irradiated by 100-Me V proton is investigated. The simulation results indicate that the most sensitive position of the Si Ge HBT device is the emitter center, where the protons pass through the larger collector-substrate(CS) junction. Furthermore, in this work the experimental studies are also carried out by using 100-Me V proton. In order to consider the influence of temperature on SEE, both simulation and experiment are conducted at a temperature of 93 K. At a cryogenic temperature, the carrier mobility increases, which leads to higher transient current peaks, but the duration of the current decreases significantly.Notably, at the same proton flux, there is only one single event transient(SET) that occurs at 93 K. Thus, the radiation hard ability of the device increases at cryogenic temperatures. The simulation results are found to be qualitatively consistent with the experimental results of 100-Me V protons. To further evaluate the tolerance of the device, the influence of proton on Si Ge HBT after gamma-ray(^(60)Coγ) irradiation is investigated. As a result, as the cumulative dose increases, the introduction of traps results in a significant reduction in both the peak value and duration of the transient currents.

Influence of interface states, conduction band offset, and front contact on the performance of a-SiC：H(n)/c-Si(p)heterojunction solar cells

P-type silicon heterojunction（SHJ） solar cells with a-SiC：H（n） emitters were studied by numerical computer simulation in this paper. The influence of interface states, conduction band offset, and front contact on the performance of a-SiC：H（n）/c-Si（p） SHJ solar cells was investigated systematically. It is shown that the open circuit voltage（Voc） and fill factor（F F） are very sensitive to these parameters. In addition, by analyzing equilibrium energy band diagram and electric field distribution, the influence mechanisms that interface states, conduction band offset, and front contact impact on the carrier transport, interface recombination and cell performance were studied in detail. Finally, the optimum parameters for the a-SiC：H（n）/c-Si（p） SHJ solar cells were provided. By employing these optimum parameters, the efficiency of SHJ solar cell based on p-type c-Si was significantly improved.

Perovskite/silicon-based heterojunction tandem solar cells with 14.8%conversion efficiency via adopting ultrathin Au contact

A rising candidate for upgrading the performance of an established narrow-bandgap solar technology without adding much cost is to construct the tandem solar cells from a crystalline silicon bottom cell and a high open-circuit voltage top cell.Here,we present a four-terminal tandem solar cell architecture consisting of a selffiltered planar architecture perovskite top cell and a silicon heterojunction bottom cell.A transparent ultrathin gold electrode has been used in perovskite solar cells to achieve a semi-transparent device.The transparent ultrathin gold contact could provide a better electrical conductivity and optical reflectance-scattering to maintain the performance of the top cell compared with the traditional metal oxide contact.The four-terminal tandem solar cell yields an efficiency of 14.8%,with contributions of the top（8.98%）and the bottom cell（5.82%）,respectively.We also point out that in terms of optical losses,the intermediate contact of self-filtered tandem architecture is the uppermost problem,which has been addressed in this communication,and the results show that reducing the parasitic light absorption and improving the long wavelength range transmittance without scarifying the electrical properties of the intermediate hole contact layer are the key issues towards further improving the efficiency of this architecture device.

Electronic transport properties of an (8,0) carbon/silicon-carbide nanotube heterojunction

A two-probe system of the heterojunction formed by an （8, 0） carbon nanotube （CNT） and an （8, 0） silicon carbide nanotube （SiCNT） was established based on its optimized structure. By using a method combining nonequilibrium Green＇s function （NEGF） with density functional theory （DFF）, the transport properties of the het-erojunction were investigated. Our study reveals that the highest occupied molecular orbital （HOMO） has a higher electron density on the CNT section and the lowest unoccupied molecular orbital （LUMO） mainly concentrates on the interface and the SiCNT section. The positive and negative threshold voltages are ＋1.8 and -2.2 V, respectively.

Sub-gap defect density characterization of molybdenum oxide: An annealing study for solar cell applications

The application of molybdenum oxide in the photovoltaic field is gaining traction as this material can be deployed in doping-free heterojunction solar cells in the role of hole selective contact.For modeling-based optimization of such contact,knowledge of the molybdenum oxide defect density of states(DOS)is crucial.In this paper,we report a method to extract the defect density through nondestructive optical measures,including the contribution given by small polaron optical transitions.The presence of defects related to oxygen-vacancy and of polaron is supported by the results of our opto-electrical characterizations along with the evaluation of previous observations.As part of the study,molybdenum oxide samples have been evaluated after post-deposition thermal treatments.Quantitative results are in agreement with the result of density functional theory showing the presence of a defect band fixed at 1.1 eV below the conduction band edge of the oxide.Moreover,the distribution of defects is affected by post-deposition treatment.

Conjugated Polymers as Hole Transporting Materials for Solar Cells

In principle,conjugated polymers can work as electron donors and thus as low-cost p-type organic semiconductors to transport holes in photovoltaic devices.With the booming interests in high-efficiency and low-cost solar cells to tackle global climate change and energy shortage,hole transporting materials(HTMs)based on conjugated polymers have received increasing attention in the past decade.In this perspective,recent advances in HTMs for a range of photovoltaic devices including dye-sensitized solar cells(DSSCs),perovskite solar cells(PSCs),and silicon(Si)/organic heterojunction solar cells(HSCs)are summarized and perspectives on their future development are also presented.