Simulation and experimental study of a novel bifacial structure of silicon heterojunction solar cell for high efficiency and low cost

A novel structure of Ag gridlSiNx/n＋-c-Si/n-c-Si/i-a-Si：H/p＋-a-Si：HlTCO/Ag grid was designed to increase the ef- ficiency of bifacial amorphous/crystalline silicon-based solar cells and reduce the rear material consumption and production cost. The simulation results show that the new structure obtains higher efficiency compared with the typical bifa- cial amorphous/crystalline silicon-based solar cell because of an increase in the short-circuit current （Jsc）, while retaining the advantages of a high open-circuit voltage, low temperature coefficient, and good weak-light performance. Moreover, real cells composed of the novel structure with dimensions of 75 mm×75 mm were fabricated by a special fabrication recipe based on industrial processes. Without parameter optimization, the cell efficiency reached 21.1% with the Jsc of 41.7 mA/cm^2. In addition, the novel structure attained 28.55% potential conversion efficiency under an illumination of AM 1.5 G, 100 mW/cm^2. We conclude that the configuration of the Ag grid/SiNx/n＋-c-Si/n-c-Si/i-a-Si：H/p＋-a-Si：H/TCO/Ag grid is a promising structure for high efficiency and low cost.

Optical simulation of external quantum efficiency spectra of CuIn_(1-x)Ga_xSe_2 solar cells from spectroscopic ellipsometry inputs

Applications of in-situ and ex-situ spectroscopic ellipsometry （SE） are presented for the development of parametric expressions that define the real and imaginary parts （ε1, ε2） of the complex dielectric function spectra of thin film solar cell components. These spectra can then be utilized to analyze the structure of complete thin film solar cells. Optical and structural/compositional models of complete solar cells developed through least squares regression analysis of the SE data acquired for the complete cells enable simulations of external quantum efficiency （EQE） without the need for variable parameters. Such simulations can be compared directly with EQE measurements. From these comparisons, it becomes possible to understand in detail the origins of optical and electronic gains and losses in thin film photovoltaics （PC） technologies and, as a result, the underlying performance limitations. In fact, optical losses that occur when above-bandgap photons are not absorbed in the active layers can be distinguished from electronic losses when electron-hole pairs generated in the active layers are not collected. This overall methodology has been applied to copper indium-gallium diselenide （Culn1-xGaxSe2; CIGS） solar cells, a key commercialized thin film PV technology. CIGS solar cells with both standard thickness （〉2 μm） and thin （〈1 μm） absorber layers are studied by applying SE to obtain inputs for EQE simulations and enabling comparisons of simulated and measured EQE spectra. SE data analysis is challenging for CIGS material components and solar cells because of the need to develop an appropriate （ε1, ε2） database for the CIGS alloys and to extract absorber layer Ga profiles for accurate structural/compositional models. For cells with standard thickness absorbers, excellent agreement is found between the simulated and measured EQE, the latter under the assumption of 100% collection from the active layers, which include the CIGS bulk and CIGS/CdS heterojunction interface layers. For cells with thin absorbers, however, an observed difference between the simulated and measured EQE can be attributed to losses via carrier recombination within a- 0.15 μm thickness of CIGS adjacent to the Mo back contact. By introducing a carrier collection probability profile into the simulation, much closer agreement is obtained between the simulated and measured EQE. In addition to the single spot capability demonstrated in this study, ex-situ SE can be applied as well to generate high resolution maps of thin film multilayer structure, component layer properties and their profiles, as well as short-circuit current density predictions. Such mapping is possible due to the high measurement speed of 〈1 s per （ , 4） spectra achievable by the multichannel ellipsometer.

Homogenizing the sulfonic acid distribution of DMF-modified PEDOT:PSS films and perovskite solar cells

Inverted perovskite solar cells using pristine PEDOT:PSS as the hole-transporting layer (HTL) have been widely studied for its less hysteresis and low-temperature preparation technologies. However, this device suffers from an inferior open-circuit voltage (VOC) and stability problems. Several attempts have made on film formation and interface engineering to improve the efficiency. Modification proved beneficial to decrease energy offset at the interface between the HTL layer and the adjacent perovskite layer. In this paper, modification PEDOT:PSS layers were realized with a dimethyl formamide (DMF) solvent. The sulfonic acid distribution was homogenized in the normal directi on after modification. The work function of the modified PEDOT:PSS layers increased from 4.71 to 5.07eV, and the conductivity of modified PEDOT:PSS increased from 3×10^-4 to 0.45 S/cm. The as-deposited perovskite films were more uniform with larger grain sizes and less pinholes, resulting in an improved VOC from 0.93 to 1.048 V, while the efficiency was increased from 11.5% to 16.8%. Solar cells without encapsulation under the 50 h and 50% humidity aging test showed 7% degradation of fill factor (FF) with 50 v/v% PEDOT:PSS layer, while the fill factor decreased 11.2% in the 0 v/v% PEDOT:PSS layer, respectively.

Properties of Boron-doped μc-Ge:H Films Deposited by Hot-wire CVD

Boron-doped hydrogenated microcrystalline Germanium （lac-Ge：H） films were deposited by hot-wire CVD. H2 diluted G-ell4 and B2H6 were used as precursors and the substrate temperature was kept at 300 ℃. The properties of the samples were analyzed by XRD, Raman spectroscopy, Fourier transform infrared spectrometer and Hall Effect measurement with Van der Pauw method. It is found that the films are partially crystallized, with crystalline fractions larger than 45% and grain sizes smaller than 50 nm. The B-doping can enhance the crystallization but reduce the grain sizes, and also enhance the preferential growth of Ge （220）. The conductivity of the films increases and tends to be saturated with increasing diborane-to-germane ratio RB2H6. All the Hall mobilities of the samples are larger than 3.8 cmZV-1·s-1. A high conductivity of

Performance of n-type silicon/silver composite anode material in lithium ion batteries: A study on effect of work function matching degree

In this paper, two types of silicon（Si） particles ball-milled from n-type Si wafers, respectively, with resistivity values of 1 Ω·cm and 0.001 Ω·cm are deposited with silver（Ag）. The Ag-deposited n-type 1-Ω·cm Si particles（nl-Ag） and Ag-deposited n-type 0.001-Ω·cm Si particles（n0.001-Ag） are separately used as an anode material to assemble coin cells,of which the electrochemical performances are investigated. For the matching of work function between n-type 1-Ω·cm Si（nl） and Ag, nl-Ag shows discharge specific capacity of up to 683 mAh·g^-1 at a current density of 8.4 A·g^-1, which is40% higher than that of n0.001-Ag. Furthermore, the resistivity of nl-Ag is lower than half that of n0.001-Ag. Due to the mismatch of work function between n-type 0.001-Ω·cm Si（n0.001） and Ag, the discharge specific capacity of n0.001-Ag is 250.2 mAh·g^-1 lower than that of nl-Ag after 100 cycles.

Simulation of a-Si:H/c-Si heterojunction solar cells: From planar junction to local junction

In order to obtain higher conversion efficiency and to reduce production cost for hydrogenated amorphous silicon/crystalline silicon(a-Si:H/c-Si) based heterojunction solar cells, an a-Si:H/c-Si heterojunction with localized p–n structure(HACL) is designed. A numerical simulation is performed with the ATLAS program. The effect of the a-Si:H layer on the performance of the HIT(heterojunction with intrinsic thin film) solar cell is investigated. The performance improvement mechanism for the HACL cell is explored. The potential performance of the HACL solar cell is compared with those of the HIT and HACD(heterojunction of amorphous silicon and crystalline silicon with diffused junction) solar cells.The simulated results indicate that the a-Si:H layer can bring about much absorption loss. The conversion efficiency and the short-circuit current density of the HACL cell can reach 28.18% and 43.06 m A/cm^2, respectively, and are higher than those of the HIT and HACD solar cells. The great improvement are attributed to(1) decrease of optical absorption loss of a-Si:H and(2) decrease of photocarrier recombination for the HACL cell. The double-side local junction is very suitable for the bifacial solar cells. For an HACL cell with n-type or p-type c-Si base, all n-type or p-type c-Si passivating layers are feasible for convenience of the double-side diffusion process. Moreover, the HACL structure can reduce the consumption of rare materials since the transparent conductive oxide(TCO) can be free in this structure. It is concluded that the HACL solar cell is a promising structure for high efficiency and low cost.

Enhanced near-infrared responsivity of silicon photodetector by the impurity photovoltaic effect

The near-infrared responsivity of a silicon photodetector employing the impurity photovoltaic （IPV） effect is investigated with a numerical method. The improvement of the responsivity can reach 0.358 A/W at a wavelength of about 1200 nm, and its corresponding quantum efficiency is 41.1%. The origin of the enhanced responsivity is attributed to the absorption of sub-bandgap photons, which results in the carrier transition from the impurity energy level to the conduction band. The results indicate that the IPV effect may provide a general approach to enhancing the responsivity of photodetectors.

Low-temperature phase transformation of CZTS thin films

The low temperature phase transformation in the Cu_2ZnSnS_4（CZTS） films was investigated by laser annealing and low temperature thermal annealing.The Raman measurements show that a-high-power laser annealing could cause a red shift of the Raman scattering peaks of the kesterite（KS） structure and promotes the formation of the partially disordered kesterite（PD-KS） structure in the CZTS films,and the low-temperature thermal annealing only shifts the Raman scattering peak of KS phase by several wavenumber to low frequency and the broads Raman peaks in the low frequency region.Moreover,the above two processes were reversible.The Raman analyses of the CZTS samples prepared under different process show that the PD-KS structure tends to be found at low temperatures and low sulfur vapor pressures.Our results reveal that the control of the phase structure in CZTS films is feasible by adjusting the preparation process of the films.

Molecular dynamics study of anisotropic growth of silicon

Based on the Tersoff potential, molecular dynamics simulations have been performed to investigate the kinetic coefficients and growth velocities of Si（100）,（110）,（111）, and（112） planes. The sequences of the kinetic coefficients and growth velocities are μ（（100））〉 μ（（110））〉 μ（（112））〉 μ（（111））and v（（100））〉 v（（110））〉 v（（112））〉 v（（111））, respectively, which are not consistent with the sequences of the interface energies, interplanar spacings, and melting points of the four planes. However,they agree well with the sequences of the distributions and diffusion coefficients of the melting atoms near the solid–liquid interfaces. It indicates that the atomic distributions and diffusion coefficients affected by the crystal orientations determine the anisotropic growth of silicon. The formation of stacking fault structure will further decrease the growth velocity of the Si（111） plane.

Control of epitaxial growth at a-Si:H/c-Si heterointerface by the working pressure in PECVD

The epitaxial-Si（epi-Si） growth on the crystalline Si（c-Si） wafer could be tailored by the working pressure in plasmaenhanced chemical vapor deposition（PECVD）.It has been systematically confirmed that the epitaxial growth at the hydrogenated amorphous silicon（a-Si：H）/c-Si interface is suppressed at high pressure（hp） and occurs at low pressure（1p）.The hp a-Si：H,as a purely amorphous layer,is incorporated in the 1p-epi-Si/c-Si interface.We find that：（i） the epitaxial growth can also occur at a-Si：H coated c-Si wafer as long as this amorphous layer is thin enough;（ii） with the increase of the inserted hp layer thickness,lp epi-Si at the interface is suppressed,and the fraction of a-Si：H in the thin films increases and that of c-Si decreases,corresponding to the increasing minority carrier lifetime of the sample.Not only the epitaxial results,but also the quality of the thin films at hp also surpasses that at lp,leading to the longer minority carrier lifetime of the hp sample than the lp one although they have the same amorphous phase.

Formation of Epitaxial Heavy-doped Silicon Films by PECVD Method

Plasma-enhanced CVD（PECVD） epitaxy at 200℃ was used to deposit heavy doped n-type silicon films. Post-annealing by rapid thermal processing was applied to improve the properties of the epitaxial layer. By analyzing the Raman spectra and the imaginary part of the dielectric constant spectra of the samples, it was found that high-quality heavy-doped epitaxial n-type silicon layer can be obtained by optimizing the parameters of the PECVD depositing process. Reducing the electrodes distance of the PECVD had a great effect on the crystallzation of the epitaxialed n-type silicon films. Sillicon films with high-crystallization were obtained with the electrodes distance of 18 mm. Post-annealing process can improve the crystallization and reduce the resistance of the epitaxial films. In our research, it was found that the sheet resistance（R□） of the post-annealed films with thickness of about 50 nm has a simple relationship with RPH3/SiH4（ratio of the flow rate of PH3 and SiH4） of the PECVD processing： R□=-184-125 lg（R（PH3/SiH4））. In the end, high-quality epitaxial n-type silicon film was obtained with R□ of 15 Ω/□ and thickness of ~50 nm.

Small molecule interfacial cross-linker for highly efficient two-dimensional perovskite solar cells

The nonradiative recombination of charge carriers at the hole transport layer(HTL)/perovskite interface generally induces remarkable performance loss of the inverted two-dimensional perovskite solar cells(2D PSCs). Herein, a cross-linkable small molecule of 2-mercaptoimidazole(2-MI) was introduced into the nickel oxide(NiO_(x))/2D perovskite interface. Experiments have confirmed the formation of Ni-N covalent bond by N atom in the 2-MI and Ni in the NiO_(x) and the coordinating between S atom of 2-MI and under-coordinated Pb^(2+) near to the NiO_(x)/perovskite interface, which contributes to creating a crosslinking between NiO_(x)/perovskite interface to restrain charge carrier recombination and enhance the extraction of hole carriers at the interface. Besides, the 2-MI modification layer is also beneficial for promoting the crystallinity of 2D perovskite. Consequently, the inverted 2D PSCs with 2-MI modification achieved the best power conversion efficiency of 15%. This paves a route to acquire highly efficient 2D PSCs by constructing a cross-linking at the NiO_(x)HTL/2D perovskite interface.

Photoemission cross section：A critical parameter in the impurity photovoltaic effect

A numerical study has been conducted to explore the role of photoemission cross sections in the impurity photovoltaic（IPV） effect for silicon solar cells doped with indium. The photovoltaic parameters（short-circuit current density, opencircuit voltage, and conversion efficiency） of the IPV solar cell were calculated as functions of variable electron and hole photoemission cross sections. The presented results show that the electron and hole photoemission cross sections play critical roles in the IPV effect. When the electron photoemission cross section is 10^-20cm^2, the conversion efficiencyη of the IPV cell always has a negative gain（△η 0） if the IPV impurity is introduced. A large hole photoemission cross section can adversely impact IPV solar cell performance. The combination of a small hole photoemission cross section and a large electron photoemission cross section can achieve higher conversion efficiency for the IPV solar cell since a large electron photoemission cross section can enhance the necessary electron transition from the impurity level to the conduction band and a small hole photoemission cross section can reduce the needless sub-bandgap absorption. It is concluded that those impurities with small（large） hole photoemission cross section and large（small） electron photoemission cross section,whose energy levels are near the valence（or conduction） band edge, may be suitable for use in IPV solar cells. These results may help in judging whether or not an impurity is appropriate for use in IPV solar cells according to its electron and hole photoemission cross sections.

Short Annealing:a Shortcut for Efficient Perovskite Solar Modules

Photo of a minimodule and its electroluminescence in dark captured by an infrared responsive camera under a forward bias of 12 V.(b)The I-V curves of a small cell(8 mm 2)and a minimodule(21.5 cm 2)under AM1.5 illumination.(c)The efficiency of a minimodule under different illumination intensity.(d)The V OC of devices as a function of illumination intensity with perovskite films annealed for 3 min during an aging period of 0 days,3 days,9 days,and 20 days.(e)XRD patterns of perovskites annealed for 3 min and 20 min before and after aging.

Spontaneous relaxation of 2D passivation layer contributes to the aging-induced performance enhancement of perovskite solar cells

The aging-induced performance enhancement of the perovskite solar cells(PSCs)has been considered to be associated with the oxidation progress of the hole-transporting layer.Whereas the influence of the structural evolution of the passivation layer is underestimated.In this work,a spontaneous relaxation of two-dimensional(2D)passivation layer with increased n-value structure is observed,which can be accelerated under ambient atmosphere.It is demonstrated that device with relaxed 2D passivation layer exhibits reduced non-radiative recombination and optimized charge transfer property,contributing substantially to the aging-induced performance enhancement in 2D-3D heterostructured PSCs.Finally,a high fill factor of 84.15%of the devices is obtained with the relaxed 2D passivation layer,suggesting the spontaneous relaxation of 2D passivation layer is playing a key role in achieving high quality optoelectronic devices.

Recent advances on interface engineering of perovskite solar cells

Lead halide perovskite solar cells(PSCs)have been rapidly developed in the past decade.Owing to its excellent power conversion efficiency with robust and low-cost fabrication,perovskite quickly becomes one of the most promising candidates for the next-generation photovoltaic technology.With the development of PSCs,the interface engineering has witnessed its increasingly critical role in maximizing the device performance as well as the long-term stability,because the interfaces in PSCs are closely correlated with the defect management,carrier dynamics and surface passivation.This review focuses on interfacial modification between the perovskite active layer and the charge transport layer,as well as the recent advances on high-efficiency and stable PSCs driven by interface engineering strategies.The contributing roles of interface engineering in terms of defect passivation,inhibiting ion migration,optimization of energy band alignment and morphological control are discussed.Finally,based on the latest progress and advances,strategies and opportunities for the future research on interface engineering for PSCs are proposed to promote the development of perovskite photovoltaic technology.

Analysis of the double-layer a-Si：H emitter with different doping concentrations for α-Si：H/c-Si heterojunction solar cells

Double-layer emitters with different doping concentrations （DLE） have been designed and prepared for amorphous silicon/crystalline silicon （ct-Si：H/c-Si） hetero- junction solar cells. Compared with the traditional single layer emitter, both the experiment and the simulation （AFORS-HET, http：//www.paper.edu.cn/html/releasepaper/2014/04/282/） prove that the double-layer emitter increases the short circuit current of the cells significantly. Based on the quantum efficiency （QE） results and the current-voltage-temperature analysis, the mechanism for the experimental results above has been investigated. The possible reasons for the increased current include the enhancement of the QE in the short wavelength range, the increase of the tunneling probability of the current transport and the decrease of the activation energy of the emitter layers.

Effects of Hot Wire Temperature on Properties of GeSi:H Films with High Hydrogen Dilution by Hot-Wire Chemical Vapor Deposition

GeSi:H films are prepared by hot-wire chemical vapor deposition(CVD) with high hydrogen dilution, DH=98%. Effects of hot wire temperature(Tw) on deposition rate, structural properties and bandgap of GeSi:H films are studied with surface profilemeter, Raman spectroscopy, Fourier transformed infrared spectroscopy, and UV-VIS-NIR spectrophotometer. It is found that the deposition rate(Rd) goes up with increasing of Tw, but increasing rate of Rd declines when Tw≥1 550 ℃. High Tw is beneficial to the formation of Ge-Si, but it has little effect on relative contents of the hydrogen bonds(Ge-H, Si-H, etc.) in the films. In the Tw range of 1 400-1 850 ℃, the maximum bandgap of the GeSi:H films is 1.39 eV at Tw =1 450 ℃ and the band gap decreases with Tw increasing when Tw≥1 450 ℃.

Efficient carrier transport via dual-function interfacial engineering using cesium iodide for high-performance perovskite solar cells based on NiOx hole transporting materials

As a famous hole transporting material, nickle oxide (NiOx) has drawn enormous attention due to its low cost and superior stability. However, the relatively low conductivity and high-density surface trap states of NiOx severely limit device performance in solar cell applications. Interfacial engineering is an efficient approach to achieve remarkable hole-transporting performance by surface passivation. Herein, the efficient NiOx hole transport layer was prepared by surface passivation engineering strategy via facile solution processes with cesium iodide (CsI). It is demonstrated that CsI plays a super-effective dual-function role in inverted solar cell device: On one hand, the presence of CsI hugely passivates the surface trap states at the NiOx/perovskite interface along with obviously improved conductivity by the incorporated Cs^(+);on the other hand, the ions immigration is significantly suppressed by the presence of I ion for high-quality perovskite films, resulting in a stable contact interface. The ameliorative interface leads to largely reduced carrier non-radiative recombination, attributing to boosted carrier extraction efficiency. As a result, decent power conversion efficiency (PCE) of 18.48% with a noticeable fill factor (FF) beyond 80% was achieved. This facile and efficient surface engineering approach with dual-function shows excellent potential for the design of high-performance functional interfacial modification layer to achieve high-performance solar cells.

Plasmon-induced trap filling at grain boundaries in perovskite solar cells

The deep-level traps induced by charged defects at the grain boundaries(GBs)of polycrystalline organic-inorganic halide perovskite(OIHP)films serve as major recombination centres,which limit the device performance.Herein,we incorporate specially designed poly(3-aminothiophenol)-coated gold(Au@PAT)nanoparticles into the perovskite absorber,in order to examine the influence of plasmonic resonance on carrier dynamics in perovskite solar cells.Local changes in the photophysical properties of the OIHP films reveal that plasmon excitation could fill trap sites at the GB region through photo-brightening,whereas transient absorption spectroscopy and density functional theory calculations correlate this photo-brightening of trap states with plasmon-induced interfacial processes.As a result,the device achieved the best efficiency of 22.0%with robust operational stability.Our work provides unambiguous evidence for plasmon-induced trap occupation in OIHP and reveals that plasmonic nanostructures may be one type of efficient additives to overcome the recombination losses in perovskite solar cells and thin-film solar cells in general.