Heterojunction Research Articles

An experimental study for thermal sensing applications of PP and PN heterojunctions fabricated in the same architecture and under the same conditions

In this research, Ni/p-GO@Fe3O4/p-Si (P–P) and Ni/ p-GO@Fe3O4/n-Si (P–N) heterojunctions (HJs) were constructed under the same conditions. Current–voltage (I–V) measurements of devices over a wide temperature range were investigated. Thermionic emission theory was used to evaluate the temperature-dependent I–V characteristics. The ideality factor (n), barrier height (Φ), rectification ratio (RR) and turn-on voltage (V 0), which are the main HJ parameters of the HJs, were determined as a function of temperature and it was seen that all parameters were dependent on temperature. The n, RR, and V 0 values for both devices decreased with increasing temperature, while Φ increased. This was attributed to the inhomogeneity between p-GO@Fe3O4 and Si. The thermal sensitivity (S) and activation energy of both devices were calculated and it was seen that S decreased linearly with increasing current. Furthermore, the highest sensitivity and the lowest activation energy values were determined as 1.35 mV K−1 and 0.79 eV, respectively for P–P HJ. These values were calculated as 0.97 mV K−1 and 0.66 eV for P–N HJ, respectively.

Temperature dependency of electronic and optoelectronic performance of 2,4-Bis[4-(N,N-dibenzylamino)-2,6-dihydroxyphenyl]squaraine/n-Si organic/inorganic heterojunction for photovoltaic application

The potential of squaraine dyes in solar cells lies in their ability to strongly absorb in the visible and near-infrared regions, as well as their high molar absorptivity. Vacuum deposition was used to prepare a heterojunction (HJ) of 2,4-Bis[4-(N,N-dibenzylamino)-2,6 dihydroxyphenyl]squaraine dye (SQ) thermally deposited onto n-type Si wafer. The SQ film was analyzed using atomic force microscopy, which revealed an average grain size of 35 nm. X-ray diffraction procedure was applied to recognize the internal crystal structural properties of the SQ film deposited onto n-type Si wafer, showing that it has a nanostructure with a crystal size of 23 nm. The absorption study revealed that the SQ film has two band gaps, measuring 1.71 and 2.23 eV. The electronic properties of the SQ/n-Si HJ were analyzed under varying temperatures (298–378 K) in dark conditions. The current density-voltage (J-V) and capacitance-voltage (C–V) procedures were applied to extract the diode parameters of SQ/n-Si HJ, which displayed temperature-dependent behavior. The SQ/n-Si HJ exhibited photovoltage conductivity under light, allowing for the evaluation of photovoltaic parameters. At room temperature, 7.596 mA/cm2, 0.625 V, and 2.04% corresponding to photovoltaic parameters of SQ/n-Si HJ were obtained for short-circuit current (Jsc), open-circuit voltage (Voc) and power conversion efficiency (PCE%), respectively. However, it was observed that these photovoltaic parameters decreased as the temperature increased. These findings suggest that the SQ/n-Si HJ has the potential for utilization in photovoltaic devices.

Role of doping concentration, thickness of intrinsic layer and number of layers of graphene in Graphene-Silicon heterojunction solar cells

Graphene has unique characteristic of zero band-gap. Its electrical properties can be widely tuned by varying the number of layers or by doping as p or n type with different materials. Due to high optical transmittance and zero band-gap, graphene can be used as both, electron, and hole extraction layer. We have simulated n-graphene/Silicon hetero-structure Ag/ITO/n-Graphene/a-Si:H/c-Si(p)/Ag using AFORS (Automat FOR Simulation of HETero structures) software under AM1.5 illumination and power density of 100 mW/cm2. Here, the thickness of a-Si:H i-layer from 0 to 20 nm, the n-type doping concentration of Graphene from 1 × 1010cm−3 to 1 × 1020cm−3 to get the optimized results. Corresponding to that, we studied the band diagram and hence barrier height, Quantum efficiency etc. The best power conversion efficiency obtained is 18.59% where the Voc is 611.8 mV, Jsc is 37.04 mA/cm2 and FF is 82.03% corresponding to i-layer thickness 5 nm, single layer graphene and n-type doping concentration of 1 × 1020cm−3.

Device engineering of p-CuAlO2/β-Ga2O3 interface: A staggered-gap band-alignment

In this work, by controlling the oxygen flow rate (OFR) (from 0% to 30%), we suggest using a p-type copper aluminum oxide (p-CuAlO2) interlayer to enhance the high breakdown and low leakage current for β-Ga2O3-based power device applications. Results of AFM measurements on p-CuAlO2 films performed using various OFRs demonstrate that greater OFRs result in an increase in film roughness payable to the unavoidable leading of defects/oxygen vacancy (VO). We used XPS and TEM analysis to validate the surface elemental compositions, chemical states, band offsets and microstructural properties of p-CuAlO2/β-Ga2O3 heterojunction (HJ) with different OFRs. With increasing OFR from 0% to 17.6%, the VBO and CBO values of HJ were decreased from 1.73 eV to 1.23 eV and from 0.53 eV to 0.38 eV respectively. Then, with increasing OFR from 17.6% to 30%, VBO was decreased from 1.23 eV to 1.13 eV while CBO increased from 0.38 eV to 0.58 eV. The staggered-gap (type-II) across the p-CuAlO2/β-Ga2O3 HJ is identified the entire OFRs. The rising tendency of optical bandgap (Eg) of p-CuAlO2 with range of OFRs, a maximum Eg of 4.35 eV was obtained with OFR of 30%. Furthermore, the electrical and carrier transport properties of p-CuAlO2/β-Ga2O3 HJ were studied using I–V and C–V techniques. The reverse breakdown voltage (Vbr) of HJ is strongly dependent on OFRs. With increasing OFRs, Vbr was decreased from 937 V to 924 V, and then to 1000 V with increasing OFR from 0% to 17.6% and then to 30%. In addition, a decrease in the interface state density (NSS) with increasing OFRs was observed which indicates that oxygen may be an effective surface passivation. Analysis confirmed that Poole-Frenkel emission dominates the reverse leakage current of all the HJ samples. The type-II p-CuAlO2/β-Ga2O3 HJ may facilitate the design and manufacture of high-performance β-Ga2O3-based heterojunctions and advance optoelectronic devices.

Photodiodes from Hetero Junctions of Intrinsic 4H-SiC and Si Semiconductor Materials

Photodiodes from Hetero Junctions of Intrinsic 4H-SiC and Si Semiconductor Materials

Transport properties of B and N sites vacancy defects graphene/h-BN heterostructures: First-principles study

First-principles calculations based on spin-polarized DFT-D2 approach have been carried out to study the transport properties of graphene/h-BN (G/h-BN) heterostructure (HS), 1 N vacancy defect in G/h-BN (G/h-BN_1 N), nearest neighbour of 1 N & 1B vacancy defects in G/h-BN (G/h-BN_nBN), and alternate zone of 1 N & 1B vacancy defects in G/h-BN (G/h-BN_aBN) materials. Transport properties like electrical conductivity (σ), electronic contribution of thermal conductivity (K), Seebeck coefficient (S) and thermoelectric power factor (P) are estimated through Boltzmann transport equations (BTE) within constant relaxation time approximation (RTA). Quantum ESPRESSO and BoltzTrap packages are used as a computational tool in the calculations. The considered materials are found to be stable van der Waals (vdWs) HS. The σ and K of graphene, h-BN, G/h-BN, G/h-BN_1 N, G/h-BN_nBN and G/h-BN_aBN are found to be increasing monotonically with temperature. The defected materials have slightly less value of σ than that of G/h-BN due to the effect of their effective mass and carrier concentration. At room temperature, K of G/h-BN, G/h-BN_nBN and G/h-BN_aBN retains similar value, while K of G/h-BN_1 N has increased slightly because the increase in Fermi velocity of electrons near Fermi level due to the reduction in effective mass thereby increasing the mean free path. We have analyzed the temperature dependent (constant value of energy) and energy dependent (constant value of temperature) S and P of above-mentioned materials, and found that S and P of defected HS are higher than that of non-defected HS materials due to combine dependence of n, T and m* on the value of S. The estimated S and P values of considered materials are consistent with reported value. Hence, they have budding employment in the thermoelectric devices.

A reconfigurable binary/ternary logic conversion-in-memory based on drain-aligned floating-gate heterojunction transistors

A new type of heterojunction non-volatile memory transistor (H-MTR) has been developed, in which the negative transconductance (NTC) characteristics can be controlled systematically by a drain-aligned floating gate. In the H-MTR, a reliable transition between N-shaped transfer curves with distinct NTC and monolithically current-increasing transfer curves without apparent NTC can be accomplished through programming operation. Based on the H-MTR, a binary/ternary reconfigurable logic inverter (R-inverter) has been successfully implemented, which showed an unprecedentedly high static noise margin of 85% for binary logic operation and 59% for ternary logic operation, as well as long-term stability and outstanding cycle endurance. Furthermore, a ternary/binary dynamic logic conversion-in-memory has been demonstrated using a serially-connected R-inverter chain. The ternary/binary dynamic logic conversion-in-memory could generate three different output logic sequences for the same input signal in three logic levels, which is a new logic computing method that has never been presented before.

Electrochemical High-Performance Hybrid Supercapacitors of Carbon Nanosphere Doped 3D Zr (II) Linked 4-{[(1E)-1-Hydroxy-3-Oxoprop-1-En-2-Yl]Sulfanyl}Benzoic Acid Metal Organic Frameworks

In the present research work, carbon nanosphere (5 wt. %, 10 wt. % and 15 wt. %)/Zr- based metal organic frame works (CNS: Zr (II)-MOFs) with different molar ratios of the legend 4-{[(1E)-1-Hydroxy-3-Oxoprop-1-En-2-yl] Sulfanyl} Benzoic Acid (HOSBA) have been successfully synthesized by hydrothermal method. Studies using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) have validated certain structural, optical, and morphological features. The supercapacitance performance of the synthesized MOFs was investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). At a current density of 0.5 A g-1 and at a scan rate of 10 mV/s, the 15% CNS doped Zr-MOF demonstrated highest specific capacitance (Cs) of 239.4 F g-1. 15 wt.% CNS doped Zr-MOF proven power density of 2100 W kg-1 and maximum energy density of 14.82 Wh Kg-1 with capacitive retention of 77.63 % following 2000 cycles mark this combination a good for supercapacitors (SCs) material. Regardless of the synthetic conditions, we achieved MOFs which exhibited hetero structure formation with spherical morphologies. The results open us new and energy approach for the supercapacitor of the Zr-metal based MOFs and applications in the photonics, optoelectronics, and promising electrode material for electrochemical energy storage systems.

Prediction of direct Z-scheme H and H́-phase of MoSi2N4/MoSX (X = S, Se) van der Waals heterostructures: A promising candidate for photocatalysis

Photocatalysis has emerged as an appealing strategy for environmental remediation and sustainable energy production. The density functional theory (DFT) approximations were employed to investigate the heterostructures (HTS) of 2H and 2H́ polymorphs of MoSi2N4/ MoSX (X = S, Se) for photocatalytic applications. To ensure their applicability for water-splitting photocatalysis, we examined the heterostructures for desirable electronic properties. The structures (except 2H́-MoSi2N4/MoSSe) have a direct Z-scheme type-II alignment which further favors the carrier separation causing hydrogen and oxygen production at distant positions. The bandgaps of structures lie within the desirable range of 1.23 to 3 eV, favoring visible light absorption. The difference in the work function of monolayers (of about 0.5 to 1 eV) develops an electric field at the interface of HTS, causing the separation of carriers. The reduction potential lies between −3.8 to −4.6 eV, while the oxidation potential lies between −5.7 to −6.2 eV. It indicates that although oxidation potentials incorporate water redox levels, reduction potentials of some HTS do not. To ensure HER, Gibbs free energies were calculated. The vacancy defects at S/Se site gave ΔGH∗ less than the catalytic threshold of 0.2 eV. Due to ultrafast charge transfer, broad spectral response, and improved photocatalytic capability due to the formation of radicals at the surface, heterostructures can act as a competitive choice over monolayers for water-splitting photocatalysis.

To improve device performance of self-driven heterojunction photodetectors by inserting a thin layer of silver nanoparticles into the electron-transporting layer

Lead selenide colloidal quantum dots (CQDs) are widely used in infrared photodetectors due to their size-dependent bandgap tunability, facile solution-processing techniques and low cost. Heterojunctions (HJs) are usually used to construct device to facilitate the separation of excitons and the transportation of photogenerated carriers. Based on the solution-processed HJ photodetector ITO/ZnO/PbSe/Ag, in which PbSe CQDs layer acts as the active layer and ZnO nanoparticles (NPs) layer as the electron-transporting layer, a greatly enhanced-performance was obtained after inserting 10 nm Ag NPs layer within the ZnO NPs layer close to the HJ ZnO/PbSe interface. By optimizing the concentration of Ag NPs solutions and the location of Ag NPs thin layer in ZnO film, the maximum responsivity of the self-driven HJ photodetector ITO/ZnO(50 nm):Ag-NPs(10 nm):ZnO(50 nm)/PbSe(300 nm)/Ag reaches to 6.25 mA/W with a specific detectivity D* of 5.17 ×1011 Jones under 8.5 μW/cm² 1550 nm illumination at zero bias. Further, the underlain physical mechanisms for the enhanced-performance were discussed in details. In this way, it provides a very efficient method for enhanced-performance self-driven HJ photodetectors by inserting a thin layer of metal NPs into the electron-transporting layer close to the heterojunction interface.

Solar Photovoltaic Parameter Extraction for Three Different Technologies Using Particle Swarm Optimization Method

Industry and academia are becoming more interested in solar energy. The problem of providing an alternative to fossil fuels and limiting the environmental damage brought on by their emissions is what has brought about this increased focus. Solar photovoltaic is the subject of a growing number of studies. The goal of the current investigation is to investigate how various technological modules namely single junction amorphous silicon (a-Si), Hetero junction with Intrinsic Thin-layer (HIT) and multi crystalline silicon (mc-Si) are affected by seasonal spectrum variation respond to Indian climatic circumstances. Compared to many other nations, the entire Indian subcontinent has a relatively distinct climate with distinct seasonal patterns. The four seasons that are considered in this study are summer, winter, monsoon, and post monsoon. The impact of each season varies on the spectrum. Such a study will be helpful to measure the parameter connected to the spectrum and assess its impact on the effectiveness of the PV array. In order to conduct accurate performance investigations, the extraction of the right circuit model parameters is essential. The estimation of the solar PV parameter is done by using Particle swarm optimization (PSO) algorithm.

Excitation-Dependent High-Lying Excitonic Exchange via Interlayer Energy Transfer from Lower-to-Higher Bandgap 2D Material.

High light absorption (∼15%) and strong photoluminescence (PL) emission in monolayer (1L) transition metal dichalcogenides (TMDs) make them ideal candidates for optoelectronic device applications. Competing interlayer charge transfer (CT) and energy transfer (ET) processes control the photocarrier relaxation pathways in TMD heterostructures (HSs). In TMDs, long-distance ET can survive up to several tens of nm, unlike the CT process. Our experiment shows that an efficient ET occurs from the 1Ls WSe2-to-MoS2 with an interlayer hexagonal boron nitride (hBN), due to the resonant overlapping of the high-lying excitonic states between the two TMDs, resulting in enhanced HS MoS2 PL emission. This type of unconventional ET from the lower-to-higher optical bandgap material is not typical in the TMD HSs. With increasing temperature, the ET process becomes weaker due to the increased electron-phonon scattering, destroying the enhanced MoS2 emission. Our work provides new insight into the long-distance ET process and its effect on the photocarrier relaxation pathways.

2D/2D Janus BiTeCl/GeSe vdW heterostructure as a robust high-performance S-scheme photocatalyst for water splitting

Two-dimensional (2D) S-scheme van der Waals (vdW) heterostructures (HSs) have aroused much interest as advanced photocatalysts due to their strong redox ability and light utilization. In this work, we have proposed a 2D/2D vdW HS composed of Janus BiTeCl monolayer (ML) and GeSe ML, and systematically investigated its photocatalytic performance using first-principles calculations. Our results show that the HS exhibits an appropriate electronic band in which the existence of intrinsic built-in electric field from GeSe ML to BiTeCl ML enhances the separation of photo-induced electron-hole pairs and certifies a S-scheme mechanism in the HS. Furthermore, the optical and electronic properties of the HS are nearly independent of either biaxial or uniaxial strain, showing robustness of the HS applied in an ever-changing environment. Notably, the HS can achieve spontaneously solar-driven water splitting and exhibits an enhanced solar-to-hydrogen (STH) efficiency up to 19.27 % owing to its S-scheme mechanism and wide range of light absorption with high absorption coefficient. Our results give insights to the structure, electronic and photocatalytic properties of 2D/2D Janus BiTeCl/GeSe vdW HS and may provide a promising S-scheme photocatalyst for overall water splitting.

A Ka-Band 64-Element Deployable Active Phased-Array TX on a Flexible Hetero Segmented Liquid Crystal Polymer for Small Satellites

A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Ka$</tex-math> </inline-formula> -band 64-element deployable active phased-array transmitter (TX) on a hetero segment liquid crystal polymer (LCP) substrate for small satellites is proposed. The proposed phased-array TX achieved a large array size implementation and a small form factor with integrated six-layer and two-layer LCP substrates. Antenna and transmission line designs considering hetero layer structure are presented in detail. Achieving 46.7 dBm electronically isotropically radiated power (EIRP), the proposed phased-array TX can support 256-APSK DVB-S2X. As a result, the proposed deployable active phased-array TX successfully realizes low-launch cost with a 9.65 g lightweight and large antenna aperture size with superior EVM performance.

Effect of lateral straggle parameter on Hetero Junction Dual Gate Vertical TFET

In this Article, the effects of lateral straggle parameter variation and Temperature variation have been investigated on Hetero Junction Dual Gate Vertical TFET. Although the TFET is a viable alternative to the MOSFET, the performance of the device is dependent on the accuracy of the fabrication process. The ion implantation technology is applied for the regions of Source/Drain during the fabrication process to realise the variation in tilt angle. As a result of this process, Dopants from the source and drain areas are extended into the channel, which has a substantial impact on the device's performance. The impact of lateral straggle is implemented by considering it in the TCAD simulation. The performance of the Hetero Junction Dual Gate Vertical TFET is examined by the 0–6 nm variation in the lateral straggle parameter. When the lateral straggling parameter (σ) is set at higher values, the greater electron tunnelling rate results in an increase in the on current. Various parameters such as intrinsic capacitances like gate to source capacitance (Cgs), gate to drain capacitance (Cgd), and total capacitance (Cgg), gate charge, electric field, surface potential, transconductance are studied in Hetero Junction Dual Gate Vertical TFET for various σ values.

High temperature annealing on vertical p-n junction p-NiO/n-β-Ga2O3 nanowire arrays for high performance UV photodetection

The authors of this article reported the effects of annealing on performance of GLAD synthesized vertical p-NiO/n-β-Ga2O3 heterostructure (HS) nanowire (NW) arrays based UV photodetector (PD). The authors further investigated the structural, optical and electrical properties at various annealing temperatures (200 °C, 400 °C, 600 °C, 800 °C, and 1000 °C) including as deposited sample to find the best sample for UV PD application. The XRD analysis showed improved crystallinity and least dislocation density and micro strain values for 800 °C sample. However, the sample degrades beyond 800 °C owing to crystallographic defects that are formed at higher annealed temperatures. Furthermore, the photoluminescence analysis showed that the defect levels decreased at 800 °C annealed temperature which was also analogous to the XPS analysis. The FE-SEM analysis also showed the impact of high temperature annealing (800 °C) with increased in nanowire diameter and length. The surface roughness was also found to be smoother for 800 °C sample from TEM analysis. Moreover, the fabricated 800 °C annealed vertical p-NiO/n-β-Ga2O3 axial NW arrays based UV PD showed the largest responsivity (Rλ) of 940 A/W as compared to all the samples. Also, the 800 °C annealed UV PD exhibited fast response speed along with rise time and fall times of 0.32 s and 0.49 s respectively. The superior performance of 800 °C sample was ascribed to the large grain size, defect reduction and improvement of interference quality.

Coexistence of Rashba effect and spin–valley coupling in TiX2 (X = Te, S, and Se) based heterostructures

Spin–orbit coupling (SOC) combined with broken inversion symmetry plays a key role in inducing Rashba effect. The combined spontaneous polarization and Rashba effect enables controlling a material's spin degrees of freedom electrically. In this work, we investigated an electronic band structure for several combinations of TiX2 monolayers (X = Te, S, and Se): TiTe2/TiSe2, TiTe2/TiS2, and TiSe2/TiS2. Based on the observed orbital hybridization between the different monolayers in these heterostructures (HSs), we conclude that the most significant Rashba splitting occurs in TiSe2/TiS2. Subsequently, we used fluorine (F) as an adatom over the surface of TiSe2/TiS2 at hollow and top sites of the surface to enhance the Rashba intensity, as the F adatom induces polarization due to the difference in charge distribution. Furthermore, by increasing the number of F atoms on the surface, we reinforced the band splitting, i.e., we observe Rashba splitting accompanied by Zeeman splitting at the valence-band edge states. Berry curvatures at K and K′ with equal and opposite nature confirm the existence of valley polarization. The computationally observed properties suggest that these HSs are promising candidates for spin–valley Hall effect devices and other spintronic applications.

Layered–Control Approach to Tune The Mobility of Perovskite SrTiO3: A Density Functional Theory Prospects

The advancement of epitaxial technology has enabled the simulation of oxide heterostructures (HS) with unique interfacial material characteristics not found in bulk materials. Recent discoveries of emergent phenomena of definite oxide interfaces have attracted much attention to oxide HS. This work explored the possibility of tuning the electron mobility of SrTiO3 (STO) through CaSnO3/SrTiO3 and ZnSnO3/SrTiO3 HSs, based on density functional theory (DFT). Own to the Sn–5s states of CSO and ZSO with more substantial band dispersion than Ti–3d states of STO, near conduction band minimum (CBM), our simulated results suggest that the bandgaps of CSO/STO (0.502 eV) and ZSO/STO (0.349 eV) HS systems are much smaller than bulk STO (1.802 eV). The effective electron masses also show much smaller values (0.31 and 0.40 m0) and (0.38 and 0.52 m0) for (CSO)7/(STO)4 and (ZSO)1/(STO)4 for HS systems compared to bulk STO (7.03 and 0.94 m0) along Γ–X and Γ–M direction. The bandgap and effective electron masses results suggest that the bandgap of STO can be well controlled and tuned by the thin film layer numbers of CSO and ZSO with better electron transportability.

Research Progress and Improvement Methods of Highly Efficient and Stable Perovskite/Silicon-based Heterojunction Tandem Cells

In recent years, in order to cope with climate and energy issues for green transformation, many countries have successively laid out the solar photovoltaic industry, making the photovoltaic industry the fastest growing industry in the energy sector. Among them, perovskite tandem cells (TSCs) are an important development direction. The stacked cells composed of perovskite top cells (PSCs) and silicon-based heterojunction (HJT) cells currently achieve a maximum photovoltaic conversion efficiency (PCE) of 31.25% and have great potential for development. This paper reviews the research and development process of the perovskite/silicon-based HJT tandem battery, and analyzes the methods to improve its PCE and stability through the research on the structure of the top, bottom and transition layers of the perovskite/silicon-based HJT tandem battery, in order to provide useful information in the industrial development and application.

Open circuit voltage reduction due to recombination at the heterojunction solar cell edge

Today to achieve high efficiency solar cells, the crystalline silicon (c-Si) heterojunction (HJ) represents one of the best available options. The key factor of its success is the high open circuit voltage (Voc) achievable, because of the excellent surface passivation due to the intrinsic amorphous silicon (a-Si:H) layers. During cells manufacturing, the a-Si:H film deposition is simultaneously performed on both c-Si wafer sides, and consequently also on the edges of the wafer. However, the wafer edges could result non-passivated in many cases such as the so-called shingling manufacturing route.Moreover, at laboratory level it is quite common to manufacture small area cells from larger wafers. When a silicon edge is left uncovered by cutting, a recombining region is created due to the silicon non-passivated surface. This, in principle, leads to a reduction in the Voc of the cell.Nevertheless, this is not experienced for large area cells cut in half but it is commonly observed that cutting silicon HJ edges results in a lowering in Voc. In this work we have analyzed the correlation between the Voc, the cell area and the recombining surface introduced by cutting the cell into a smaller one. We have monitored the Voc as a function of the cell area during time, and we also have investigated the possibility of a re-passivation of the cell edges by depositing a thick a-Si:H layer after masking the sun exposed cell surface, exploring different deposition conditions to avoid re-annealing of the existing a-Si:H layers.