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Laser doping of silicon with pulsed and scanned laser beams is now well-established to obtain defect-free, doping profile tailored, and locally selectively doped regions with a high spatial resolution. Picking the correct laser parameters (pulse power, pulse shape, and scanning speed) impacts the depth and uniformity of the melted region geometry. This work performs laser doping on the surface of single crystalline silicon, using a pulsed and scanned laser profile with a Gaussian intensity distribution. A deposited boron oxide precursor layer serves as a doping source. Increasing the local inter-pulse distance x irr between subsequent pulses causes a quadratic decrease of the sheet conductance G sh of the doped surface layer. Here, we present a simple geometric model that explains all experimental findings. The quadratic dependence stems from the approximately parabolic shape of the individual melted regions directly after the laser beam has hit the Si surface. The sheet resistance depends critically on the intersection depth d ch and the distance x irr of overlap between two subsequent, neighboring pulses. The intersection depth d ch quadratically depends on the pulse distance x irr and therefore also on the scanning speed v scan of the laser. Finally, we present a simple model that reduces the complicated three dimensional, laterally inhomogeneous doping profile to an effective two-dimensional, homogeneously doped layer which varies its thickness with the scanning speed. [ABSTRACT FROM AUTHOR]

We investigated laser parameters for a laser doping (LD) process that enables to improve cell characteristics through the formation of a selective emitter (SE) multicrystalline silicon solar cell. In this work, the aim is the formation of SE with an investigation of the effect of critical LD parameters, such as laser power and laser speed. The LD 532 nm is used to obtain highly doped regions and deep doping depth that will receive the screen printed silver grid contact. The optimized laser power and speed of 80% (54.08 w), 500 mm/s, induced the activation of the phosphorus dopant and its diffusion in the silicon then leads to a local decrease of the emitter sheet resistance from 60 Ω/sqr to 30 Ω/sqr. Moreover, it was determined by SIMS and ECV measurements that the dopant concentration increased and the doping depth became deeper in the selective emitter formed by increasing laser power and/or laser speed. Fortunately, the surface cracks damage were not observed. The only damage caused by laser irradiation evidenced by debris and a melted surface. We have successfully developed SE p-type mc-Si 4 inch wafer produced by CRTSE solar cell with FF significantly improved of 1.01%. This gain is due to improved short-circuit current density and open-circuit voltage. [ABSTRACT FROM AUTHOR]

Semi-insulating (SI) 4H-polytype of silicon carbide (SiC) is a highly desirable wide bandgap semiconductor material for various applications in challenging environments owing to its exceptional characteristics such as high melting point, remarkable thermal conductivity, strong breakdown field, and excellent resistance to oxidation. This study investigates the critical laser processing parameters to operate a pulsed UV 355 nm laser to dope high-purity (HP) SI 4H-SiC substrates with boron. The doping process parameters are examined and simulated for this UV laser doping system using a liquid precursor of boron. Boron atoms create a dopant energy level of 0.3 eV in the doped HP 4H-SiC substrates. Diffusion of boron atoms into 4H-SiC substrates modifies the hole density at 0.3 eV energy level, and causing a variation in the dynamic refraction index, and absorption index. Consequently, the optical properties of boron doped samples, namely, transmittance, reflectance, and absorbance, can be modified. The current simulation reported in this study explains the motivation of UV optical doping strategy to dope SiC substrates. A beam homogenizer was used to control the laser spot used to generate doping process. The advantage of the beam homogenizer is demonstrated by producing flat-top beams with uniform intensity over a certain area defined by the focusing lens choice. A simple theoretical model is used to select the laser processing parameters for doping SiC substrates. These modeled parameters are used to determine the efficient laser processing parameters for our doping experiments. [ABSTRACT FROM AUTHOR]

Interdigitated back contact (IBC) architecture can yield among the highest silicon wafer‐based solar cell conversion efficiencies. Since both polarities are realized on the rear side, there is a definite need for a patterning step. Some of the common patterning techniques involve photolithography, inkjet patterning, and laser ablation. This work introduces a novel patterning technique for structuring the rear side of IBC solar cells using the enhanced oxidation characteristics under the locally laser‐doped n++ back surface field (BSF) regions with high‐phosphorous surface concentrations. Phosphosilicate glass layers deposited via POCl3 diffusion serve as a precursor layer for the formation of local heavily laser‐doped n++ BSF regions. The laser‐doped n++ BSF regions exhibit a 2.6‐fold increase in oxide thickness compared to the nonlaser‐doped n+ BSF regions after undergoing high‐temperature wet thermal oxidation. The utilization of oxide thickness selectivity under laser‐doped and nonlaser‐doped regions serves two purposes in the context of the IBC solar cell, first patterning rear side and second acting as a masking layer for the subsequent boron diffusion. Proof‐of‐concept solar cells are fabricated using this novel patterning technique with a mean conversion efficiency of 20.41%. [ABSTRACT FROM AUTHOR]

Laser doping of n-type 4H-silicon carbide (SiC) semiconductor substrates with boron (B) using a pulsed Nd:YAG laser (λ = 1064 nm) is reported. An aqueous boric acid solution was used as a boron precursor. A simple theoretical heat transfer model was employed to select the laser processing parameters, i.e., laser power and laser-substrate interaction time, and determine the appropriate temperature to dope 4H-SiC substrates. The selected processing parameters ensured that the temperature at the laser-substrate interaction zone was below the SiC peritectic temperature to prevent any crystalline phase transformations in SiC. Fourier-transform infrared spectrometry was conducted to determine the optical properties of both undoped and boron-doped 4H-SiC substrates within the mid-wave infrared (MWIR) wavelength range (3–5 μm). Boron atoms create an acceptor energy level at 0.29 eV above the valence band in the 4H-SiC bandgap, which corresponds to λ = 4.3 μm. Boron-doped 4H-SiC substrate exhibited reduced reflectance and increased absorptance for the MWIR range. An absorption peak at λ = 4.3 μm was detected for the doped substrate. This confirmed the creation of the acceptor energy level in the 4H-SiC bandgap and, thus, doping of 4H-SiC with boron. A notable decrease in the refractive index, i.e., from 2.87 to 2.52, after laser doping of n-type 4H-SiC with boron was achieved. [ABSTRACT FROM AUTHOR]

An n-type layer was formed in p-type CdTe via the laser-induced back-side doping of In with a Nd:YAG laser. Hall effect measurements confirmed the formation of an n-type layer on the Indoped area. The In/CdTe/Au p-n diode was fabricated as a gamma-ray detector via laser-induced back-side doping. A guard-ring structure was introduced into the In anode electrode to realize an electron-collecting-type detector with a low leakage current, although pixelation on the In anode side was difficult. In the In/CdTe/Au p-n gamma-ray detector, rectification behavior was clearly observed, and the leakage current of the central electrode was 13 nA at a reverse voltage of 500 V. The energy spectra of 241Am and 57Co radioisotopes were collected at room temperature and showed energy resolutions (full width at half maximum) of 2.9 and 3.6 keV for gamma rays of 59.5 and 122 keV, respectively. [ABSTRACT FROM AUTHOR]

In this paper a simplified approach for the generation of laterally p‐ and n‐doped structures applicable for cost‐effective production of interdigitated back contact (IBC) solar cells is presented. We use a stack of doping glasses deposited by atmospheric pressure chemical vapor deposition (APCVD), consisting of borosilicate glass (BSG) and phosphosilicate glass (PSG) on Czochralski‐grown (Cz) silicon substrates. A laser process creates the p‐doped regions by local liquid phase diffusion of boron from the BSG layer into the underlying molten Cz‐Si substrate. Simultaneously, the BSG‐PSG stack is removed by laser ablation. In a subsequent high‐temperature step, phosphorus diffuses from the remaining PSG‐BSG layer into the crystalline silicon substrate under inert gas atmosphere, creating complementary to laser doped areas n+‐doped regions. By the use of APCVD, phosphorus and boron contents of the doping glasses can be adjusted freely to vary the resulting p‐ and n‐doped profiles. A higher boron content in the BSG layer enhances the diffusion of phosphorus through the BSG, especially at lower diffusion temperatures. The resulting doping profiles are characterized using electrochemical capacitance‐voltage measurements and the resulting sheet resistances using the four‐point probe method. The amount of minority dopant contamination in n‐ and p‐doped regions is investigated by secondary ion mass spectrometry. Furthermore, transfer length method (TLM)‐measurements indicate contactability of the generated doped regions. [ABSTRACT FROM AUTHOR]

A two-dimensional (2D) atomic crystalline transition metal dichalcogenides has shown immense features, aiming for future nanoelectronic devices comparable to conventional silicon (Si). 2D molybdenum ditelluride (MoTe2) has a small bandgap, appears close to that of Si, and is more favorable than other typical 2D semiconductors. In this study, we demonstrate laser-induced p-type doping in a selective region of n-type semiconducting MoTe2 field effect transistors (FET) with an advance in using the hexagonal boron nitride as passivation layer from protecting the structure phase change from laser doping. A single nanoflake MoTe2-based FET, exhibiting initial n-type and converting to p-type in clear four-step doping, changing charge transport behavior in a selective surface region by laser doping. The device shows high electron mobility of about 23.4 cm2V−1s−1 in an intrinsic n-type channel and hole mobility of about 0.61 cm2V−1s−1 with a high on/off ratio. The device was measured in the range of temperature 77–300 K to observe the consistency of the MoTe2-based FET in intrinsic and laser-dopped region. In addition, we measured the device as a complementary metal–oxide–semiconductor (CMOS) inverter by switching the charge-carrier polarity of the MoTe2 FET. This fabrication process of selective laser doping can potentially be used for larger-scale MoTe2 CMOS circuit applications. [ABSTRACT FROM AUTHOR]

Silicon cathodes for the efficient production of hydrogen in the photoelectrochemical process of water splitting have been created and studied. A photoactive layer on p-Si wafer was obtained by pulsed laser doping of the wafer with phosphorus from a solution of orthophosphoric acid. A film of amorphous molybdenum sulfide (a-MoSx) up to 4 nm thick was deposited on the surface of the modified n+p-Si wafer. This caused a significant increase in photocurrents in the acid solution as compared to the bare n+p-Si. The composition of the catalytic film was modified during the photoelectrochemical process of hydrogen evolution. The study of the energy bands at the interface of the a-MoSx heterojunction with the n+-Si layer showed that the reaction of hydrogen evolution proceeded, probably, because of electron tunneling through the a-MoSx film. Using the density functional theory, a thermodynamic analysis of the possible effect of chemical changes on the silicon surface and in the a-MoSx film itself on the efficiency of hydrogen catalysis was carried out. [ABSTRACT FROM AUTHOR]

Bioactive glass (BG) is a frequently used biomaterial applicable in bone tissue engineering and known to be particularly effective when applied in nanoscopic dimensions. In this work, we employed the scalable reactive laser fragmentation in liquids method to produce nanosized 45S5 BG in the presence of light‐absorbing Fe and Cu ions. Here, the function of the ions was twofold: (i) increasing the light absorption and thus causing a significant increase in laser fragmentation efficiency by a factor of 100 and (ii) doping the BG with bioactive metal ions up to 4 wt%. Our findings reveal an effective downsizing of the BG from micrometer‐sized educts into nanoparticles having average diameters of <50 nm. This goes along with successful element‐specific incorporation of the metal ions into the BG, inducing co‐doping of Fe and Cu ions as verified by energy‐dispersive X‐ray spectroscopy (EDX). In this context, the overall amorphous structure is retained, as evidenced by X‐ray powder diffraction (XRD). We further demonstrate that the level of doping for both elements can be adjusted by changing the BG/ion concentration ratio during laser fragmentation. Consecutive ion release experiments using inductively‐coupled plasma mass spectrometry (ICP‐MS) were conducted to assess the potential bioactivity of the doped nanoscopic BG samples, and cell culture experiments using MG‐63 osteoblast‐like cells demonstrated their cytocompatibility. The elegant method of in situ co‐doping of Fe and Cu ions during BG nanosizing may provide functionality‐advanced biomaterials for future studies on angiogenesis or bone regeneration, particularly as the level of doping may be adjusted by ion concentrations and ion type in solution. [ABSTRACT FROM AUTHOR]

Single-crystal Si (c-Si) bottom-gate thin-film transistors (BG-TFTs) were fabricated using all sputtering processes. Laser doping from sputter-deposited Sb-doped amorphous Si film was proposed, by which n+ c-Si with resistivity and contact resistivities of 1.5 × 10âˆ'3 Ωcm and 2.1 × 10âˆ'5 Ωcm2, respectively, were fabricated. In addition, thin (50 nm) and low-heat conductive titanium was proposed for BG to realize continuous lateral crystal growth in Si film above the edge of BG. The fabricated n-channel c-Si BG-TFTs exhibited a field-effect mobility of 75 ± 21 cm2 Vâˆ'1sâˆ'1, subthreshold swing of 0.612 ± 0.110 Vdecâˆ'1, and threshold voltage of 4.9 ± 1.38 V. Lack of bottom Si/SiO2 interface quality was indicated to be the origin of insufficient mobility. [ABSTRACT FROM AUTHOR]

We present laser-doped interdigitated back contact (IBC) solar cells with efficiencies of 23% on an area of 244 cm2 metallized by a screen-printed silver paste. Local laser doping is especially suited for processing IBC cells where a multitude of pn-junctions and base contacts lay side by side. The one-sided deposition of boron-doped precursor layers by atmospheric pressure chemical vapor deposition (APCVD) is a cost-effective method for the production of IBC cells without masking processes. The properties of the laser-doped silicon strongly depend on the precursor's purity, thickness, and the total amount of boron dopants. Variations of the precursor in terms of thickness and boron content, and of the laser pulse energy density, can help to tailor the doping and sheet resistance. With saturation-current densities of 70 fA/cm2 at sheet resistances of 60 Ohm/sq, we reached maximum efficiencies of 23% with a relatively simple, industrial process for bifacial IBC-cells, with 70% bifaciality measured on the module level. The APCVD-layers were deposited with an inline lab-type system and a metal transport belt and, therefore, may have been slightly contaminated, limiting the efficiencies when compared to thermal-diffused boron doping. The use of an industrial APCVD system with a quartz glass transport system would achieve even higher efficiencies. [ABSTRACT FROM AUTHOR]

We demonstrated that p- and n-type activation layers can be formed in Si films by laser doping with H3PO4 solution and Al2O3 sol coating. The phosphorus and aluminum concentrations at the laser doped region were found to be over 1019 cm-3 in Si films. In addition, generations of the activation carriers for n- and p-type layers were confirmed by Hall effects measurement. In this study, the characteristic of CMOS invertors fabricated by laser doping are presented.

Two-dimensional (2D) transitional metal dichalcogenides (TMDs) have garnered significant attention due to their potential for next-generation electronics, which require device scaling. However, the performance of TMD-based field-effect transistors (FETs) is greatly limited by the contact resistance. This study develops an effective strategy to optimize the contact resistance of WSe 2 FETs by combining contact doping and 2D metallic electrode materials. The contact regions were doped using a laser, and the metallic TaSe 2 flakes were stacked on doped WSe 2 as electrodes. Doping the contact areas decreases the depletion width, while introducing the TaSe 2 contact results in a lower Schottky barrier. This method significantly improves the electrical performance of the WSe 2 FETs. The doped WSe 2 /TaSe 2 contact exhibits an ultralow Schottky barrier height of 65 meV and a contact resistance of 11 kΩ·μm, which is a 50-fold reduction compared to the conventional Cr/Au contact. Our method offers a way on fabricating high-performance 2D FETs.

Abstract In this work, we investigate the use of advanced hydrogenation and low-temperature diffusion processes (a 3 h 700 °C process after emitter diffusion) for the electrical neutralization of laser-induced defects for laser doped and grooved solar cells. Despite the laser doping and grooving (LDG) process being performed before silicon nitride passivation to avoid thermal expansion mismatch between the silicon and the silicon nitride layer, some crystallographic defects are still formed during the process. The application of a low-temperature diffusion process increases implied open circuit voltages by 14 mV, potentially due to phosphorus diffusion of dislocated regions induced during laser processing. Laser hydrogenation is shown to be capable of passivating the majority of the remaining laser-induced defects. Over 1% absolute improvement in efficiency is achieved on cells with a full area aluminum back surface field. Preliminary results with minimal optimization demonstrate efficiencies of over 19% with a full area Al back contact cell. The potential to achieve much higher voltages when used with a passivated rear is also demonstrated. Highlights • A new laser grooving process that simultaneously dopes the groove walls has been developed. • The novel process has demonstrated the ability to form narrow grooves of only 3–5 µm width in preparation for metal contact formation. • The application of a low-temperature diffusion process significantly increases the implied open circuit voltages by 14 mV. • Laser hydrogenation is shown capable of passivating the majority of the remaining laser-induced defects. • Over 1% absolute improvement in efficiency is achieved. • Preliminary results demonstrate efficiencies of over 19% on industrial full area aluminum back surface field solar cells. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) are semiconductor devices that emit light in a narrow-band spectrum with wavelengths ranging from the infrared to the ultraviolet. This paper will look at current state of the art of the fabrication and doping techniques of silicon carbide (SiC) as a light conversion material for nitride LEDs. SiC has a wide bandgap and high thermal conductivity. When properly doped, SiC also exhibits photoluminescence behaviour. Due to these properties, SiC has been touted as a possible replacement material for phosphors in nitride LEDs. Phosphors have a short lifetime and contain rare earths which are very expensive. LEDs made with phosphors have a poor colour rendering index and have a short degradation time. In order to overcome these shortcomings, the technology of producing SiC as a light conversion material has to be perfected so as to make it a viable alternative to phosphors. [ABSTRACT FROM AUTHOR]

We study a boron tribromide (BBr 3 ) diffusion process with second deposition realized by active nitrogen flow through the BBr 3 bubbler at the end of the process with respect to laser doping. Compared to the reference BBr 3 diffusion without second deposition, the new BBr 3 diffusion provides a two times higher boron dose within the borosilicate glass (BSG)/silicon dioxide (SiO 2 ) stack layer grown on the silicon surface. The second deposition leads to both thinning of the intermediate SiO 2 layer and 11 nm-growth of the BSG layer, which results in an 8 nm thicker BSG/SiO 2 stack layer with a total thickness of 42 nm. These altered properties of the BSG/SiO 2 layer facilitate the formation of laser-doped selective boron emitters, while the second deposition hardly affects the as diffused charge carrier concentration profile. The obtained emitter properties, sheet resistance R sh ≈ 100 Ω/sq and emitter dark saturation current density j 0e ≈ 25 fA/cm 2 (textured surface, Al 2 O 3 /SiN X passivation) for the photoactive part of the emitter are not affected by the introduced second deposition step. For the laser-doped part of the emitter, the charge carrier concentration after laser doping is higher for the BBr 3 diffusion with second deposition resulting in stronger local doping with up to 10 Ω/sq lower R sh . The application of an analytical model to calculate specific contact resistances ρ C in dependence of e.g. dopant concentration of the laser-doped profiles and crystallite penetration depth d cryst reveals that ρ C is expected to benefit largely from the altered profile shapes due to laser doping for the BBr 3 diffusion with second deposition. A relative decrease in ρ C of up to 90% and 50% is found for small d cryst (depth of several tens of nm) and large d cryst (depth of several hundreds of nm), respectively. Another potential advantage of the second deposition holds for emitter dark saturation current densities at the metal-silicon interface j 0,met . A 3D simulation model that is based on metal crystallites penetrating into the emitter considering the different doping profiles after laser processing yields a j 0,met ≈ 740 fA/cm 2 for small d cryst that is 14% relatively lower for the BBr 3 diffusion with second deposition. [ABSTRACT FROM AUTHOR]

Abstract: A common concern regarding plated contacts to solar cells is the adhesion strength. In this work, laser‐formed anchor points have been applied to Suntech Power's PLUTO passivated emitter and rear cells. Voltages as high as 696 mV have been achieved, showing the ability of a laser‐doped selective emitter at the front surface and localized contacts at the rear when combined with the hydrogenation of defects to reduce the device dark saturation current to well below current norms for commercial passivated emitter and rear cells. The simple hydrogen passivation process applied during sintering appears to facilitate the high voltages by significantly reducing recombination associated with the p‐type Cz wafer and laser‐induced defects formed during laser doping. The same hydrogenation process almost entirely eliminates the damage caused by laser ablation in forming the anchor points. With 50% anchor point coverage (more than necessary for adhesion equivalent to or stronger than screen‐printed contacts), an average VOC of 693 mV was achieved, with an average current of 40.5 mA/cm2, average device efficiency of 20.2%, and a single best cell of 20.5% efficiency. These cells also exhibit excellent contact adhesion and pass all thermal cycling and damp‐heat testing according to IEC 61215. [ABSTRACT FROM AUTHOR]

During the past decades, atomically thin, twodimensional (2D) layered materials have attracted tremendous research interest on both fundamental properties and practical applications because of their extraordinary mechanical, thermal, electrical and optical properties, which are distinct from their counterparts in the bulk format. Various fabrication methods, such as soft-lithography, screen-printing, colloidal-templating and chemical/ dry etching have been developed to fabricate micro/ nanostructures in 2D materials. Direct laser fabrication with the advantages of unique three-dimensional (3D) processing capability, arbitrary-shape designability and high fabrication accuracy up to tens of nanometers, which is far beyond the optical diffraction limit, has been widely studied and applied in the fabrication of various micro/ nanostructures of 2D materials for functional devices. This timely review summarizes the laser-matter interaction on 2D materials and the significant advances on laser-assisted 2D materials fabrication toward diverse functional photonics, optoelectronics, and electrochemical energy storage devices. The perspectives and challenges in designing and improving laser fabricated 2D materials devices are discussed as well. [ABSTRACT FROM AUTHOR]

Laser-assisted diffusion of phosphorus dopants has been investigated to realize selective emitters on mc-Si wafers. In this paper, we studied, in the presence of PSG, the effect of laser speed and power doping parameters on the sheet resistance R _Sq variation as a function of selective emitter formation. Four point-probe (FPP) measurements showed that 5.5–10 W with speed 100–1500 mm s ^−1 are, respectively, the best power values to form a selective emitter with 20–40 Ω/□ typical values. Electrochemical Capacitance-Voltage (ECV) results showed that dopant concentration and junction depth increased with decreasing scan speed, resulting in lower sheet resistances. Thus, the greater the difference between the concentration of starting phosphorus and that created by laser treatment, the smaller the square R _Sq will be. Scanning Electron Microscopy (SEM) images demonstrated more pronounced patterns of laser ablation when the power is high and/or the scanning speed is low.

Al is doped into 4H-SiC by irradiating pulsed KrF excimer laser to 4H-SiC immersed in AlCl 3 aqueous solution. Impact on doping depth of the use of expanded laser-pulse width is investigated. Expanded laser pulse is produced by splitting and recombining the laser beam with mirrors. The laser pulse width was expanded from its original width of 55–100 ns, while the peak power of the expanded pulse is as half as that of the original pulse under the same laser fluence. Multiple shots of the expanded laser pulses increased the doping depth at the Al concentration of 1×10 16 /cm 3 to 100 nm from 30 nm of the single shot of the original short, high-peak power laser. The increased doping depth could be due to enhanced diffusion by extra vacancies generated by the repeated laser irradiations. Due to the smaller laser peak power, the expanded pulse laser can suppress damage generation under multiple laser shots and, as a result, leakage current of the pn junction diode is kept low. [ABSTRACT FROM AUTHOR]

Interdigitated back contact (IBC) solar cells offer one of the most promising routes towards highest device efficiencies but require finding of industrially feasible low cost production sequences. In this paper, the fabrication of a 22.8% efficient all-laser-doped IBC solar cell with localized boron and phosphorus doped contacts is reported. The laser-based approach with localized emitter and back-surface field regions reported here avoids costly patterning steps of the localized contacts. By means of numerical device simulations it is demonstrated that this cell is limited by recombination and contact resistivity of the localized contacts and an efficiency potential of 23.8% with improved laser parameters is demonstrated. [ABSTRACT FROM AUTHOR]

In this work, we report on a novel structure of Interdigitated Back-Contacted (IBC) solar cells on c-Si p-type substrates that combines laser processed homojunction base contacts and silicon heterojunction (SHJ) emitters. These hybrid devices which can lead to potential benefits in device processing and/or conversion efficiency. In the proposed fabrication process special attention has been paid to the compatibility of both involved technologies: silicon heterojunction and laser doping from dielectric films. In particular, we focus on the surface passivation obtained by the heterojunction emitter after removing the aluminum oxide/silicon carbide (Al 2 O 3 /SiC x ) layer stack needed for the laser doping process and previously deposited on the c-Si surface. A severe passivation degradation after plasma etching process to remove the top SiC x film is observed, despite leaving the Al 2 O 3 film on the c-Si surface. Based on high-frequency capacitance-voltage characterization, an increase in the interface state density and a strong impact on the fixed charge density is deduced. Next, in order to choose an optimized metallization technology that could simultaneously contact both the ITO film and the p + laser processed regions, we evaluate the contact quality of Titanium and Aluminum on ITO. Results show that Titanium is a better option with a specific contact resistance of 1.1 mΩ cm 2 . Finally, finished hybrid IBC solar cells with conversion efficiencies in the 18-19% range are reported. [ABSTRACT FROM AUTHOR]

The passivated emitter and rear cell (PERC) has entered the solar cell market, and it is expected that the amount of PERC production will increase yearly in the future. Improvements in the cell efficiency have a great influence on reducing the cost of power generation. In this study, we focused on the loss of the back surface field (BSF) at the rear side of a PERC, fabricated PERCs having a local BSF including boron diffused by boron laser doping (B-LD), and evaluated this effect. The results from an analysis using scanning electron microscopy (SEM) indicated that the thickness of the BSF fabricated with B-LD was thicker than that of the BSF fabricated without B-LD. The average value of the saturation current density of the metallized area (including BSF) J 0, contact was 554 fA/cm 2 in the PERCs fabricated with B-LD and a dedicated Al paste, and the lowest value achieved was approximately 300 fA/cm 2 . The number of Kirkendall voids for the PERCs fabricated with B-LD decreased in comparison with the PERCs fabricated without B-LD. The PERCs fabricated with B-LD exhibited reduced rear-side recombination. [ABSTRACT FROM AUTHOR]

We present the development of aluminum oxide (AlO x ) and boron-doped silicon nitride (SiN x :B) layer stacks for application on the back side of monocrystalline p-type silicon wafers. Two deposition techniques are used for the deposition of the AlO x /SiN x :B layer stacks, atomic layer deposition and plasma-enhanced chemical vapor deposition. Both techniques enable excellent surface passivation with surface recombination velocities of 4 cm/s after firing. Also, heavy local doping with sheet resistances down to 20 Ω/sq is possible by laser processing. We call this concept the PassDop approach. For the laser processed area where the silicon surface is locally boron-doped and the AlO x /SiN x :B passivation layer stack is locally removed, a quite low dark saturation current density of about 900 fA/cm 2 is determined. The PassDop approach can be a solution to realize passivated emitter and rear locally doped PERL solar cells by improving their rear side properties while maintaining industrial applicability. [ABSTRACT FROM AUTHOR]

Both buried contact solar cells (BCSC) and laser doped selective emitter (LDSE) solar cells have achieved considerable success in large-scale manufacturing. Both technologies are based on plated contacts. High metal aspect ratios achieved by BCSC allow low shading loss while the buried metal contacts in the grooves provide good contact adhesion strength. In comparison, although the LDSE cell achieves significantly higher efficiencies and is a much simpler approach for forming the selective emitter region and self-aligned metal plating, the metal adhesion strength falls well short of that achieved by the BCSC. Recent studies show that plated contacts based on the latter can be more durable than screen-printed contacts. This work introduces a new concept of laser doping with grooving to form narrow grooves with heavily doped walls in a simultaneous step, with the self-aligned metal contact subsequently formed by plating. This process capitalizes on the benefits of both BCSC and LDSE cells. The laser-doped grooves are only 3–5 µm wide and 10–15 µm deep; the very steep walls of these grooves remain exposed even after the subsequent deposition of the antireflection coating (ARC). This unique feature significantly reduces the formation of laser-induced defects since the stress due to the thermal expansion mismatch between the ARC and silicon is avoided. Furthermore, the exposed walls allow nucleation of the subsequent metal plating. This novel structure also benefits from greatly enhanced adhesion of the plated contact due to it being buried underneath the silicon surface in the same way as the BCSC. Cell efficiencies over 19% are achieved by using this technology on p -type Czochralski (Cz) wafers with a full area aluminum (Al) back surface field (BSF) rear contact. It is expected that much higher voltages and consequently higher efficiencies could be achieved if this technology is combined with a passivated rear approach. [ABSTRACT FROM AUTHOR]

The effect of laser doping of Al on the gas sensing behavior of nanocrystalline ZnO thin films is reported. The doping of Al was carried out by the spin-coating of Al-precursors on nanocrystalline ZnO films followed by a pulsed laser irradiation. The laser-doped films were characterized as a function of laser power density by measuring the optical, structural, electrical, morphological and gas sensing properties of ZnO films. It was found that the laser doping process resulted in an increase of electrical conductivity of ZnO films. The performance of gas sensor was investigated for different concentrations of H 2 and NH 3 in the air. The results indicate that the laser doping process can be utilized to improve the sensor characteristics such as sensitivity and response time by optimization of laser power density. The optimum laser power is interpreted as the critical power level required to compete the effective doping versus developing the effective grain boundaries. Also, the selectivity of laser-doped ZnO sensors for H 2 was studied for a likelihood practical gas mixture composed of H 2 , NH 3 and CH 4. It is found that these films can be optimized to develop H 2 and NH 3 sensors in PPM level with a higher selectivity over other reducing gases. [ABSTRACT FROM AUTHOR]

In this paper we propose a possible process simplification for pseudosquare 15.6×15.6 cm 2 Interdigitated Back Contact (IBC) CZ-Si solar cells. By using laser doping to create a selective BSF, one out of three diffusions and a wet etching step can be avoided, compared to a completely diffusion-based process flow. We show numerical optimization of this simplified cell structure in terms of: i) rear optics with additional SiN x capping layer, ii) contact fraction of the selective BSF. The results feature a top cell efficiency of 21.7% measured over the area of 239 cm 2 . Further characterization implies that cells were limited mainly by: i) FF losses attributed to lateral majority carrier transport in the BSF region and increased J 02 losses, ii) current loss which can be related to the BSF region. [ABSTRACT FROM AUTHOR]

Deep diffusion of phosphorus atoms in monocrystalline silicon using laser doping process has been studied in this work. A pulse modulated CW fiber laser of wavelength 1070 nm with microsecond pulses has been used to diffuse phosphorus from pre-deposited spin-on-dopant film. The surface and cross-sectional morphology has been studied using SEM and AFM. The concentration-depth profiling was done using PP-TOFMS. Deep junctions of more than 10 µm have been obtained under various laser doping conditions while a maximum junction depth of 51.3 µm has been obtained through optimization. Diffusion depth enhancement is made possible by increasing the pulse length and reducing laser scan speed. Laser doping led to formation of n + region with surface concentration varying in the range of 3×10 20 –5×10 20 cm −3 for varying scan speed. Cross-sectional TEM and diffraction studies on laser irradiated samples show presence of only monocrystalline silicon phase after laser induced melting and solidification. [ABSTRACT FROM AUTHOR]

In this work, we present a novel technological approach to form highly boron-doped selective emitters. The selective emitters are formed by using a Laser Induced Forward Transfer Doping (DLIFT) process, which allows precise adjustment of the doping profile by tuning the laser parameters and choosing an appropriate doping source. Surface dopant concentrations of up to N s ≈1×10 21 cm −3 were achieved by using DLIFT. Subsequent BBr 3 tube furnace diffusion was performed to form a low surface concentration ( N s ≈1×10 19 cm −3 ) homogeneous emitter. In comparison to the conventionally applied BBr 3 tube diffusion, an increase in open circuit voltage of up to 6 mV is predicted based on the photoluminescence measurements performed after passivation, screen-printing and firing processes. Simulations suggest that this voltage gain is most possibly due to a lower emitter saturation current density ( j 0e ) of the highly doped DLIFT samples compared to the BBr 3 diffusion samples. Moreover, it is observed that the laser-induced defects are reduced successfully after a subsequent boron tribromide (BBr 3 ) tube diffusion, which is used to form the homogeneous emitter after the DLIFT process. The micro Raman spectroscopy results indicated that the compressive stress of −200 MPa in the silicon crystal lattice after DLIFT process is released by the subsequent BBr 3 tube diffusion. These results demonstrate that the DLIFT process in combination with the conventionally applied BBr 3 tube diffusion can be an effective approach to form selective boron emitters in high efficiency n -type crystalline silicon (c-Si) solar cells. [ABSTRACT FROM AUTHOR]

One challenge to the use of lightly-doped, high efficiency emitters on multicrystalline silicon wafers is the poor gettering efficiency of the diffusion processes used to fabricate them. With the photovoltaic industry highly reliant on heavily doped phosphorus diffusions as a source of gettering, the transition to selective emitter structures would require new alternative methods of impurity extraction. In this paper, a novel laser based method for gettering is investigated for its impact on commercially available silicon wafers used in the manufacturing of solar cells. Direct comparisons between laser enhanced gettering (LasEG) and lightly-doped emitter diffusion gettering demonstrate a 45% absolute improvement in bulk minority carrier lifetime when using the laser process. Although grain boundaries can be effective gettering sites in multicrystalline wafers, laser processing can substantially improve the performance of both grain boundary sites and intra-grain regions. This improvement is correlated with a factor of 6 further decrease in interstitial iron concentrations. The removal of such impurities from multicrystalline wafers using the laser process can result in intra-grain enhancements in implied open-circuit voltage of up to 40 mV. In instances where specific dopant profiles are required for a diffusion on one surface of a solar cell, and the diffusion process does not enable effective gettering, LasEG may enable improved gettering during the diffusion process. [ABSTRACT FROM AUTHOR]

We describe the manufacturing process for interdigitated back contact back junction silicon solar cells based on laser processes, and present detailed results and analysis to our best cell efficiency of 23.24%. The manufacturing process features two laser doping steps, one for the boron doped emitter and one for the phosphorus doped back surface field. The saturation current densities of thermal oxide passivated laser doped regions are on par with furnace diffused silicon for high efficiency solar cells. Laser ablation locally defines the contact areas through the rear dielectric layer stack, and structures the rear aluminum metallization. The precision of the laser systems in conjunction with the optical setup yields line shaped doping traces with a width of 150 µm and a pitch below 500 µm. The measured optical and electrical properties of our solar cell agree well with 3D simulation results. The measured reflection, transmission, quantum efficiency and current voltage curves in dark and illuminated condition simultaneously agree well with simulation, based on the same data set, giving confidence in the result of a detailed free energy loss analysis. The bulk resistive and recombination losses are identified as the main loss contributors. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Laser diffusion from PECVD layers can result in the incorporation of impurities like nitrogen into crystalline silicon. It is shown that the nitrogen can have a significant influence on the laser doping process. The incorporated nitrogen can affect the material properties resulting in misinterpretation of measurement results and accumulation of nitrogen at the surface can lead to negative effects such as improper contact formation. An approach reducing the amount of nitrogen content in the PECVD layer and the LBSF is presented. This new approach allows for a partial decoupling of the passivation and doping properties of the passivation layers. The doping efficiency of the laser doping process was significantly improved while keeping the recombination properties low. The higher doping efficiency was found to be of major importance for a reproducible level of LBSF/metal contact resistivity on the rear side. Using the adapted process with reduced nitrogen content, it is shown that the doping concentration is high enough to be contacted by screen printed silver pastes. Solar cells using the new approach are presented reaching efficiencies up to 20.9% on a cell area of 149 cm 2 . The influence of the higher doping efficiency reflected into the new solar cells allowing fill factors of up to 80.1%. [ABSTRACT FROM AUTHOR]

In the last years, there is a clear trend in c-Si solar cell fabrication to place both emitter and base contacts on the back side leading to the so-called Interdigitated Back Contacted (IBC) solar cell structure. This solar cell architecture requires excellent front and rear surface passivation as well as a very low recombination emitter. Moreover, laser doping may be an attractive technique to create both selective emitter and base contacts using appropriate dielectric layers as dopant sources, i.e. Al 2 O 3 and a-SiC x (n) stacks for the p + and n + regions respectively. In this study, we report on a simplified fabrication process for IBC n-type c-Si solar cells combining laser doping and a conventional boron emitter passivated by Al 2 O 3 films. Results show very low emitter recombination currents in the ∼10-50 fA/cm 2 range before laser processing. In addition, selective emitter contacts can be created by laser doping with recombination current densities at each contact point around 4.4 pA/cm 2 in relatively low and shallow doped boron doped profiles (sheet resistance ∼400 Ω/sq). Finally, IBC solar cells, 3 x 3 cm 2 device area, were fabricated combining selective laser-doped emitter and base contacts reaching efficiencies up to 20.8%. [ABSTRACT FROM AUTHOR]

In this work, we report on improving efficiency of DopLa cells fabricated on p-type substrates. This type of solar cells has all the highly-doped regions based on laser doping from dielectric films resulting in a very simple fabrication process. Depending on the dopant type, emitter regions or high/low doping junctions related to base contacts can be created. The emitter regions are located at the rear surface in order to be contacted by a continuous metal film without penalizing in shadowing losses, while the front surface shows a typical finger grid configuration with the base contacts under the metal. In a previous work, the reported efficiency was limited by optical losses at the front planar surface. As a consequence, we focus on the introduction of a texturized front surface to the device. Firstly, we characterize the contact formation by laser processing on texturized surfaces by SEM image showing that the size of the contacted region is difficult to determine. By measuring contact resistance and surface recombination velocity, we deduce that the laser process of such surfaces leads to a contacted region which is smaller than the one where passivation is lost. The obtained information is included in 3D simulations to get the optimum size of the contacts, i.e. optimum laser power. Additionally, a new front grid metallization is introduced in order to reduce shadowing. Due to the rear emitter configuration of these devices, front surface recombination is crucial for collecting photogenerated carriers. Thus, optimum laser power is very close to the minimum to obtain a reliable contact. Finally, 2x2 cm 2 solar cells are fabricated with a best efficiency of 17.0%. [ABSTRACT FROM AUTHOR]

In this work we have developed an innovative fabrication process of n-type interdigitated back contact (IBC) c-Silicon solar cells. The main feature is that all the highly-doped regions in the cell have been entirely fabricated through laser processing of dielectric layers, avoiding the high temperature steps typically found in conventional diffusion processes. Additionally, we have reduced the patterning steps. We use an Al 2 O 3 film deposited by thermal-ALD that passivates the front and rear surfaces acting simultaneously as antireflection coating and aluminium source for p+ emitter formation. Back surface field (BSF) is achieved by the introduction of phosphorous atoms from a N doped a-SiC x stack deposited by PECVD. This stack consists of intrinsic a-SiC x as passivating layer, a-Si (n type) as phosphorous source and a-SiC x carbon rich as protective capping layer. Dielectrics were laser processed in a point- like structure to achieve highly-doped regions. As a proof of concept we have developed four 9 cm 2 -IBC varying the emitter coverage with efficiencies up to 15.5%. However, our 3D simulations suggest that efficiency beyond 20% is reachable by future improvements in the laser process stage. [ABSTRACT FROM AUTHOR]

N-type solar cells are being developed as next generation photovoltaic solar cells, and have attracted a significant amount of attention. In addition, the demand for high-efficiency silicon solar cells has increased in order to reduce production costs and save space. In this study, we demonstrate boron laser doping (LD) using a boron-doped NanoGram® Si paste in n-type passivated emitter, rear totally diffused solar cells. The sheet resistance was 54 Ω/sq at the local boron emitter after boron LD. The boron diffusion depth was ∼2.0 μm, and the boron surface concentration was 7 × 10 19 atoms/cm 3 . The n-type solar cells were fabricated using boron LD to have front side boron selective emitters. The characteristics of the newly developed solar cells improved in comparison with those of the reference cells (i.e., those without boron selective emitters), and a maximum efficiency of 19.70% was achieved. The improved efficiency was mainly due to the increase in the short circuit current density and fill factor. [ABSTRACT FROM AUTHOR]

We present the optimization of the laser doped back surface field (BSF) for interdigitated back contact solar cells (IBC). The POCl 3 flow limits the phosphorus concentration in the phosphorus silicate glass (PSG) during furnace diffusion, hence limits the sheet resistance when used as dopant source for laser doping. The saturation current densities of quasi steady state photo conductance (QSSPC) samples correlate with the sheet resistance dependent Auger contribution simulated with EDNA 2. Utilizing the measured saturation current density and contact resistance for various sheet resistances, we optimize the BSF doping for the recently presented 23.24% efficient laser processed IBC solar cell by numerical 3D solar cell simulation. [ABSTRACT FROM AUTHOR]

We report on the progress of imec's n-type passivated emitter, rear totally diffused rear junction silicon solar cells. Selective laser doping has been introduced in the flow, allowing the implementation of a shallow diffused front surface field and a reduction of the recombination current in the contact area. Simplifications have been implemented towards a more industrial annealing sequence, by replacing expensive forming gas annealing steps with a belt furnace annealing. By applying these improvements, together with an advanced texturing process and emitter passivation by atomic layer deposition of Al2O3, 22.5% efficient cells (three busbars) have been realized on commercial 156 · 156 mm2 Czochralski-Si. This result has been independently confirmed by ISE CalLab. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• Laser hyperdoping of Si films (Si:Ti) is achieved on Si solar cells to form a p / n / n + structure. • Optical absorbance (λ = 200–2500 nm) increases due to a rough surface and hyperdoping. • Ti impurities with 5.1 at.% distribute in the entire nanocrystalline Si:Ti films. • Si:Ti solar cell achieves PCE of 18.6%, which increased by 29% than that of substrate. • Such performance is achieved by improving V OC and adding sub-bandgap photocurrent. Problems such as poor open-circuit voltage (V OC) and low photogenerated charge-carrier collection usually exist in hyperdoped Si solar cells for sub-bandgap optoelectronic response. Here, (Si/Ti) n multilayer films were deposited on the front surface of monocrystalline Si solar cells with single p / n junction. The films were melted and crystallized using a 1064-nm nanosecond-pulsed laser to form Ti-hyperdoped Si (Si:Ti) films, serving as a n + layer in the new solar cells. A reduction in light reflection, an increase in sub-bandgap infrared absorption, and a p / n / n + structure for charge-carrier collection were used to increase both the sub-bandgap and above-bangap photocurrents of solar cells. Thus, the V OC and short-circuit current density (J SC) of a Si:Ti solar cell reached 613 mV and 41.1 mA⋅cm−2, respectively. Furthermore, its sub-bandgap infrared (IR) external quantum efficiency (EQE) and J IRSC increased by ∼ 100% and 79% than those of the monocrystalline Si solar cell substrate, respectively. Finally, the solar cell with a Si:Ti film thickness of 105 nm and an active area of 14.4 cm2 showed the highest photoconversion efficiency (18.6%), which increased by 29% than that of substrate (14.4%). [ABSTRACT FROM AUTHOR]

This paper reports on the use of AAO layers as a source of p-type dopants for laser doping processes that forms localised p+ regions on Si surfaces. Sheet resistances as low as 2 Ω/sq were demonstrated when a laser was used to scribe through a region of AAO using a speed of 500 mm/s and power of 9 W. Unlike laser-doping through spin-coated polyboron sources, it was shown that laser doping through AAO layers can be performed without introducing any voids into the Si and form a local BSF ~5 µm into Si which is advantageous for PERL cell structure. This co-doping process was used to fabricate rear-passivated cells with efficiencies of up to 19.9%. However, although the heavily-doped local p + regions could reduce R s to values as low as 0.54 Ω cm 2 , there was a penalty in terms of a high ideality factor in the V mp – V oc voltage range which limited FF s to ~76%. [ABSTRACT FROM AUTHOR]

We report fabrication of nanostructured, laser-doped selective emitter (LDSE) silicon solar cells with power conversion efficiency of 18.1% and a fill factor (FF) of 80.1%. The nanostructured solar cells were realized through a single step, mask-less, scalable reactive ion etch (RIE) texturing of the surface. The selective emitter was formed by means of laser doping using a continuous wave (CW) laser and subsequent contact formation using light-induced plating of Ni and Cu. The combination of RIE-texturing and a LDSE cell design has to our knowledge not been demonstrated previously. The resulting efficiency indicates a promising potential, especially considering that the cell reported in this work is the first proof-of-concept and that the fabricated cell is not fully optimized in terms of plating, emitter sheet resistance and surface passivation. Due to the scalable nature and simplicity of RIE-texturing as well as the LDSE process, we consider this specific combination a promising candidate for a cost-efficient process for future Si solar cells. [ABSTRACT FROM AUTHOR]

The heavy B-doping of an intrinsic Si(1 0 0) wafer has been performed by irradiating a B-doped Si nanoparticle film on the surface of the Si(1 0 0) substrate with energy densities of 8.0 and 16.0 J/cm 2 by 532-nm laser light. The thicknesses of the heavily doped surface layers were investigated using Raman spectroscopy. The observed 488.0-nm-excited Raman bands were decomposed into two bands: a Fano-type band due to the heavily doped Si surface layer and a Voigt band due to the lightly doped, intrinsic Si region. The analysis of the Fano-type band indicated that the carrier concentration of the heavily doped region was larger than approximately 10 19 cm −3 . Based on the two-state model, the thicknesses of the heavily doped surface layers were 480 and 630 nm for the samples prepared with energy densities of 8.0 and 16.0 J/cm 2 , respectively. These values were consistent with those obtained by secondary ion mass spectroscopy (SIMS). [ABSTRACT FROM AUTHOR]