Rear Si Research Articles

Refined nickel nucleation and plated metal adhesion induced by pulsed light-induced plating on picosecond laser-ablated silicon solar cells

This study reports the impact of pulsed Ni light-induced plating (LIP), compared to the commonly used galvanostatic Ni LIP, on the initial Ni nucleation and subsequently plated busbar adhesion of Cu-plated laser-ablated p-type passivated emitter and rear Si solar cells. Initial Ni nucleate sizes decreased from 27.8 ± 9.1 to 25.4 ± 7.9 nm when the pulse-on current density during pulsed Ni LIP was increased from 50 to 178 mA cm−2, and were smaller than the 30.4 ± 9.7 nm nucleates observed with galvanostatic plating at 25 mA cm−2 after the same charge had been delivered to the surface. The density of Ni nucleation was also increased for pulsed LIP. This increased density of smaller Ni nucleates was attributed to the higher pulse-on currents inducing a larger surface potential which favoured nucleation over Volmer Weber 3D island growth of Ni. It also led to a greater density of adhesive anchor points along busbars which contributed to more adhesive plated contacts with busbar pull forces as high as 3 N mm−1 being measured when the pulse-on current density was 100 mA cm−2. However, it is shown that higher pulse-on current densities can result in unintended parasitic reactions, such as H2 evolution, and reduced busbar adhesion.

Efficient Hydrogen Generation and Total Nitrogen Removal for Urine Treatment in a Neutral Solution Based on a Self-Driving Nano Photoelectrocatalytic System.

Urine is the main source of nitrogen pollution, while urea is a hydrogen-enriched carrier that has been ignored. Decomposition of urea to H2 and N2 is of great significance. Unfortunately, direct urea oxidation suffers from sluggish kinetics, and needs strong alkaline condition. Herein, we developed a self-driving nano photoelectrocatalytic (PEC) system to efficiently produce hydrogen and remove total nitrogen (TN) for urine treatment under neutral pH conditions. TiO2/WO3 nanosheets were used as photoanode to generate chlorine radicals (Cl•) to convert urea-nitrogen to N2, which can promote hydrogen generation, due to the kinetic advantage of Cl−/Cl• cyclic catalysis. Copper nanowire electrodes (Cu NWs/CF) were employed as the cathode to produce hydrogen and simultaneously eliminate the over-oxidized nitrate-nitrogen. The self-driving was achieved based on a self-bias photoanode, consisting of confronted TiO2/WO3 nanosheets and a rear Si photovoltaic cell (Si PVC). The experiment results showed that hydrogen generation with Cl• is 2.03 times higher than in urine treatment without Cl•, generating hydrogen at 66.71 μmol h−1. At the same time, this system achieved a decomposition rate of 98.33% for urea in 2 h, with a reaction rate constant of 0.0359 min−1. The removal rate of total nitrogen and total organic carbon (TOC) reached 75.3% and 48.4% in 2 h, respectively. This study proposes an efficient and potential urine treatment and energy recovery method in neutral solution.

High efficiency organic-Si hybrid solar cells with a one-dimensional CdS interlayer.

A carrier-selective passivating contact is one of the main factors for the preparation of high-efficiency solar cells. In this work, a one-dimensional nanostructured CdS material combined with quasi-metallic TiN exhibits excellent contact performance with n-Si. In addition, the introduction of the CdS nanowire interlayer is more conducive to the extraction and transmission of electrons, which is attributed to a more suitable energy level alignment between the rear contact and the n-Si absorption layer. As a result, the power conversion efficiency of organic/Si solar cells based on the CdS NW/TiN/Al electron selective passivating contact exceeds 14.0%. This shows a promising technique to achieve high-performance and low-cost photovoltaic devices.

The synergic generation of CO3[rad]− and O2[rad]− radicals in a novel photocatalytic fuel cell for efficient oxidation of carbonate-containing wastewater and simultaneous electricity production

The treatment of refractory wastewater and energy utilization are challenging environmental issues. Carbonate as the most common anion abounds in the aquatic environment. Here, we proposed a novel method to degrade carbonate-containing wastewater and simultaneous electricity generation via the combined oxidation of CO3− and O2− radicals. The CO3− radical was produced by the photoelectrode of TiO2/Si photovoltaic cell with the rear Si photovoltaic cell providing external bias, and the O2− radical was produced from the generation of H2O2 on a gas diffusion electrode (GDE), and they were both further enhanced from the activation reaction of H2O2 with HCO3− electrolyte. The result showed that a high degradation ratio of 91.97 % was achieved in 120 min for a typical refractory organics of rhodamine b (RhB), which is more than double of that in traditional system by using Pt black as cathode and SO42− as electrolyte. In addition, this system could achieve electricity production with a 28.9 % increase when adding RhB. Moreover, the mechanism of efficient degradation and electricity generation were also studied. The proposed system provides a novel way for organics efficient degradation and simultaneous electricity production in carbonate-containing wastewater.

Communication—Enhancement of Boron Back-Surface-Field and Suppression of Auger Recombination to Improve Ultralow-Reflectance Si Solar Cells

A high conversion efficiency of 20.2% is achieved for simple structured-Si solar cells without a conventional anti-reflection layer. The ultralow-reflectance less than ∼3% is achieved by formation of a nanocrystalline Si (nc-Si) layer using the surface structure chemical transfer (SSCT) method which takes only 15 s. The nc-Si layer is passivated by phosphosilicate glass, while the rear Si surface is passivated by boron back-surface-field (B-BSF). By optimizing diffusion conditions, a high short-circuit current density of 41.8 mAcm−2 and improvement of an open-circuit voltage are achieved owing to enhancement of B-BSF and suppression of Auger recombination in the phosphorus-doped nc-Si layer.

Peculiar behavior of Si cluster ions in a high-energy-density solid Al plasma.

Peculiar behavior is found in a Si cluster ion, moving with a speed of ∼0.22c (c: speed of light) in a solid Al plasma in the context of cluster-ion beam driven inertial confinement fusion: The Si ion, moving closely behind the forward-moving Si ion for a distance of several Å in the cluster, feels the wake field generated by the forward Si. The acceleration interaction force on the rear Si ion by the forward-moving ion may balance with the deceleration backward force in the longitudinal-moving direction. The forward-moving Si ion would be decelerated, as an isolated ion is decelerated without correlation. However, the deceleration of the rear Si ion, moving behind closely, would be reduced significantly. The rear Si ion may catch up and overtake the forward-moving Si ion in the cluster during the Si cluster-ion interaction with the high-density Al plasma. This peculiar behavior appears when the ions are aligned well longitudinally. The wake field is confined around the Si ion in the forward and transverse directions for a distance smaller than the Si cluster interionic distance l_{c}. However, the tail of the wake field extends beyond l_{c} due to the Si ion high speed of ∼0.22c. Therefore, the peculiar behavior shown above appears only for the ions in one cluster aligned well longitudinally.

14.1% efficiency hybrid planar-Si/organic heterojunction solar cells with SnO2 insertion layer

Hybrid planar-Si/organic heterojunction solar cells have gained considerable interest in the fabrication of cost-effective and high-efficiency devices. However, most of high power conversion efficiency (PCE) performances have been obtained with particular structures, front surface texture or rear surface field layer. In this paper, we provide a simple method without complex structures, and demonstrate the superiority and the mechanism of using stannic oxide (SnO2) as an insertion layer. The SnO2 insertion layer takes the place of the Schottky barrier, which reduces barrier height of rear Si to enhance charge transfer. And the effect of the insertion layer reduces contact resistance and enhances contact quality of rear Si side. Meanwhile, it has been indicated that the Si-O-Sn bonds were formed by SnO2 and Si dangling bond (Si-), which have a passivation effect on the Si surface to effectively suppress the recombination losses. Furthermore, simulations using density functional theory (DFT) confirm that the electrostatic potential can improve electronic transmission from Si to Sn between Si-O-Sn bonds. Finally, for the hybrid planar-Si/PEDOT:PSS heterojunction solar cells without any special structures, the highest PCE of 14.1% was achieved, up 10.8% compared with that without SnO2 insertion layer. These findings provide an effective way of improving Si/metal contact via a simple, room temperature process for other photovoltaic devices.

High-Performance Conducting Polymer/Si Nanowires Hybrid Solar Cells Using Multilayer-Graphene Transparent Conductive Electrode and Back Surface Passivation Layer

Polymer/Si hybrid solar cells (HSCs) are promising for mass production because of their high performance and low cost, but several problems such as big reflective index of Si, low aperture ratio of the mesa-type metal transparent conductive electrodes (TCEs), and large recombination loss at Si rear contact should be solved for the practical applications. Here, we first report a HSC structure of multilayer graphene TCE/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/Si nanowires/n-Si/TiOx (back surface passivation layer) to cope with aforementioned problems. Resulting maximum power conversion efficiency (PCE) is 12.10%, much larger than that of the planar-Si-type HSC (10.11%) as a control sample, mainly due to the lowered reflectance (increased absorption) and recombination loss. As the active area increases from 14 to 50 mm2, the PCE decreases by only 2.5% from 12.10 to 9.60%, possibly resulting from the area-dependent change in the uniformity of the Si NWs. The PCE shows only a 10% decrease for 3...

High yield of H2O2 and efficient S recovery from toxic H2S splitting through a self-driven photoelectrocatalytic system with a microporous GDE cathode

In this paper, the toxic H2S was transformed efficiently into valuable S and H2O2 and its chemical reaction energy was converted into electric energy through a self-driven photoelectrocatalytic(PEC) system, which consisted of a microporous gas diffusion electrode(GDE) and a self-bias photoanode. In the cathode region, high yield of H2O2 up to 0.8 mmol/L/h, was achieved because of the fast gas diffusion and direct two-electron reduction of molecular oxygen on the microporous GDE cathode. In the anodic region, H2S was completely converted into S without persulfide based on a I−/I3− redox system and the production rate of S recovery was about 0.60 mmol/h, 42 times higher than before. The remarkable catalytic efficiency also benefited from the self-bias design of photoanode, which included a front photoanode of WO3 and a rear Si photovoltaic cell (Si PVC). The constituted self-driven PEC system could accelerate the charges separation and increase the electron transfer rate of PEC cell. In addition, electricity was generated simultaneously, with a maximum power density of 0.19 mW/cm2. The proposed self-driven PEC cell system offers an efficient, complete and sustainable way for H2S resourcization.

A self-sustaining monolithic photoelectrocatalytic/photovoltaic system based on a WO3/BiVO4 photoanode and Si PVC for efficiently producing clean energy from refractory organics degradation

A novel self-sustaining monolithic photoelectrocatalytic/photovoltaic (SMPP) system is constructed with a FTO-glass-based WO3/BiVO4 photoanode, which was prepared by coating BiVO4on WO3 nanoplate array using simple wet chemical methods, a rear Si photovoltaic cell (PVC) and a counter Pt-black/Pt cathode. The optimum SMPP system shows an efficient and stable degradation of tetracycline hydrochloride with a rate constant 0.75 h−1, and yields an open circuit voltage 1.35 V, a short circuit current 2900 μA cm−2, a power density 1112 μW cm−2, which is nearly 14 times that of theultimate conventional photocatalytic fuel cell to date, and a hydrogen generation rate 52.6 μmol h−1 cm−2. This outstanding performance should be due to the efficient electron/hole separation and light exploitation, because, under stimulated sunlight illumination, the front WO3/BiVO4 photoanode absorbs short-wavelength photons and generates electron/hole pairs, in which the photogenerated holes can oxidize organics, while the rear Si PVC captures the transmitting longer-wavelength photons to generate photovoltage that drives photogenerated electrons to the cathode for reducing H+ to H2 and generating electricity in the external-circuit. The results also demonstrate that various refractory organics can be efficiently decomposed along with the production of electricity and hydrogen by the SMPP system. This work provides a more efficient way to dispose organics and simultaneously produce clean energy than conventional technologies and serves well as a promising technology for wastewater recycling.

Rear texturing for light-trapping in laser-crystallised silicon thin-film solar cells on glass

This paper presents optimisation of rear Si texturing by KOH-based solution for enhanced light-trapping in liquid-phase crystallised Si thin-film solar cells on glass. Texturing with 3 µm Si removal exhibits the largest absorption enhancement (compared with 1 and 2 µm Si removal) due to the enhanced light scattering by the rear pyramidal features. In the solar cells with SiOx/SiNx/SiOx buffer layer (with anti-reflection effect), the Jsc is found to increase from 20.4 (planar reference) to 22.6 mA/cm2 (10.8% enhancement) with the optimised rear Si texturing. The Voc and pFF are not degraded. After incorporating white paint back surface reflector and front anti-reflection foil to the rear-textured solar cells, Jsc up to 25.4 mA/cm2 (24.5% relative enhancement) is achieved.

A low-cost photoelectrochemical tandem cell for highly-stable and efficient solar water splitting

The stability and cost of solar-driven water splitting system are still the main bottlenecks for its large-scale implementation. Here, an ingeniously designed low-cost photoelectrochemical tandem cell possessing three performance-superior components, i.e., a front novel photoanode of WO3 nanoplates epitaxially coated with [001]-oriented TiO2 nanoprickles, and a rear Si photovoltaic cell, and a counter-cathode of interlayer-expanded MoS2 nanostructures, is reported for highly-stable and efficient solar water splitting. The tandem cell shows a close-to-unity Coulomb efficiency for water splitting, and a high and sustained-stable solar-to-hydrogen efficiency in a 35 days’ test. The result also reveals that it is versatile in solar-driven wastewater treatment. Most importantly, the composite photoanode that, for the first time, is proposed using epitaxial-growth based on double-match, i.e. lattice match and band match, shows dramatical improvement in stability and photoelectrochemical performance, in which the photocurrent of the WO3/ TiO2 photoanode is improved by 80% without any obvious decay after 100h of continuous testing compared with a 92% decay in photocurrent for the WO3 photoanode. The epitaxial TiO2 layer facilitates interfacial charge transportations and provides a complete sealing of WO3 surfaces at an atomic level. Such efficient interfacial design and system-level integration of high-performance nanomaterials shed a unique light on the potential large-scale implementation of solar water splitting for renewable hydrogen fuel production.

Ultrathin Si solar cell with nanostructured light trapping by metal assisted etching

We report an 8µm-thick silicon solar cell with an efficiency of 9.60%. Nanostructured silicon surface formed via metal assisted etching shows a broadband reflection below 10%. Despite the excellent optical performance, a moderate short-circuit current (JSC) of 25.44mA/cm2 was collected. Relatively low external quantum efficiency (EQE) at short wavelengths was associated with carrier recombination at the enhanced surface and by the Auger process. Moreover, parasitic absorption at the back contact is the main factor resulting a relatively low EQE in long wavelength region of the spectrum. Our optical simulations show that planarization of the rear Si surface and insertion of a low refractive index dielectric spacer between Si and the rear metal can significantly reduce the parasitic absorption in the metal, resulting in JSC values over 35mA/cm2.

Low-temperature synthesis TiOx passivation layer for organic-silicon heterojunction solar cell with a high open-circuit voltage

Organic/silicon (Si) heterojunction solar cells may promise for high performance and low cost solar cell manufacture because they can combine advantages of Si and organic semiconductors. However, the performances of organic-Si solar cells were still mainly jeopardized by Si rear contact recombination losses. Here, titanium oxide (TiOx) layer via low-temperature solution synthesis way was deposited on Si rear side to reduce electrical losses. Minority carrier lifetime, transient photovoltage decay and external quantum efficiency measurements indicated that TiOx could effectively suppress the recombination losses of Si rear side, which reflected in the improvement of open circuit voltage (Voc) and long-wavelength photoresponse. Contact resistance and capacitance-voltage measurements further showed that resistance and rear adverse barrier height (Φ-) between Si and aluminum could be dramatically reduced. A power conversion efficiency (PCE) of 14.3% was achieved for textured Si/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) solar cell by incorporating TiOx layer between Si and aluminum. A Voc of 643mV was achieved based on this low-temperature processed organic-Si heterojunction solar cell. The outstanding performance was ascribed to Si-O-Ti bonding at TiOx/Si interface, which was identified by X-ray photoelectron spectroscopy. This simple low-temperature solution processed metal oxide layer provided a facile way for Si surface passivation to achieve high performance solar cells.

Enhanced Absorption in Laser-Crystallized Silicon Thin Films on Textured Glass

This paper reports enhanced absorption in laser-crystallized Si thin films on abrade-textured glass. The Si film on textured glass has large high-quality grains of several hundred micrometers in width and up to several centimeters in length. A combination of glass texturing, rear Si texturing, white paint rear reflector, and front moth-eye antireflection foil on a 10-μm-thick Si film (on $\text{SiO}_{x}/\text{SiN}_{x}/\text{SiO}_{x}$ intermediate layer) shows a large broadband absorption enhancement with potential short-circuit current densities up to 29.5 mA/cm2 (26.1% enhancement as compared with a planar reference).

Si paste technology for high-efficiency solar cells

This study demonstrates the successful implementation of industrially feasible local B doping as a local back surface field via the Si paste technology to fabricate high-efficiency solar cells. Si paste formed by 25wt% p-type Si nanoparticles and 75wt% organic solvent is used as the B source. Si paste is fully screen-printed on the preprocessed p-type Si rear surface, and then a homogenous Si cladding layer is formed by picosecond laser cladding. During this process, B diffuses into the Si substrate. The Si cladding layer itself is a heavily doped layer and forms a metallurgical bond between Si substrate. After co-firing with Al paste, cells obviously avoid Kirkendall void formation at contact regions. The heavily doped Si cladding layer and localized B doping can decrease the contact resistance and reduce the minority carrier recombination at the local metal contacts. This optimized rear surface design finally contributes to push the overall average cell efficiency over 20.3% on p-type CZ wafers.

Light Absorption Enhancement in Laser-Crystallized Silicon Thin Films on Textured Glass

Liquid-phase crystallization of Si films on textured glass by line-focus diode laser produces a material with large high-quality grains of several hundred micrometers in width and up to centimeters in length, similar to the films crystallized on planar glass. A combination of glass texturing, rear Si texturing, white paint rear reflector, and a front moth-eye antireflection foil on a 7-μm absorber results in significant broadband absorption enhancement in the Si film with potential short-circuit current densities in solar cells of $\text{27.8} \;\text{mA/cm}^{\text{2}}$ or 36.3% enhancement compared with a planar reference film without light-trapping features.

Machining on Rear Surface of a Silicon Substrate by an Infrared Femtosecond Laser via Non-linear Absorption Processes

Silicon (Si) is a semiconductor material widely used in modern technologies such as microelectronics, MEMS, and photonics. Si is an opaque material in visible to near-infrared wavelength region but it transmits any light longer than 1127nm, which corresponds to its band gap energy of 1.12eV. Therefore, Si can be considered as transparent material for radiations longer than 1127nm. Here we have proposed a new laser microprocessing method of Si, which increases the efficiency, accuracy and flexibility in machining. The thickness of the Si substrate used was 320μm and a femtosecond laser at 1552nm was focused by a 100x infrared objective lens on the rear surface of the substrate. However, only a shallow groove was formed: its depth was approximately 170nm or less. It is expected that when the laser is focused on the Si rear surface, where it is contacting with an etchant, wet etching will occur due to the temperature rise caused by the laser irradiation. Therefore, to increase the machining rate, we tried laser-assisted backside wet-etching using KOH solution as the etchant. The maximum groove depth was increased to more than 3μm. The effects of laser irradiation conditions on machined grooves were examined. The results achieved showed rather scattered values and indicated that the maximum groove depth was not always produced at high energy deposition conditions. One of the reasons might be the formation of hydrogen bubbles from the chemical reaction between Si and KOH, which block the contact of Si and KOH.

Plasmonic degradation and the importance of over-coating metal nanoparticles for a plasmonic solar cell

Plasmonics is an emerging area of study for photovoltaic applications. The last decade has seen an increasing interest in the application of metal nanoparticles (MNP) on the surface of solar cells to scatter light and subsequently achieve light trapping. In this study we investigate the optical effects of single and double layer rear light trapping reflectors – planar or scattering; direct or detached, which are fabricated on the 400μm front-planar silicon solar cells. As a single layer reflecting scheme, we find that Ag metal nanoparticles (Ag MNP) as a scattering reflector outperforms all other single layer reflectors with a maximum current enhancement of 11% (calculated from 900nm to 1200nm) compared to metal back reflectors. However over time we notice that the scattering properties are dampened due to tarnishing of the silver nanoparticles. A double layer reflecting scheme using optimised Ag nanoparticles as the first layer and the second layer of evaporated Ag (E Ag) separated via MgF2 is introduced to overcome this issue together with additional light trapping. We find that no EQE or current degradation is observed over time. More importantly, after optimising the over-coating MgF2 thickness, the best-performing double layer reflector structure improves EQE by 4.5-fold at 1160nm and enhances photocurrent by 25.6% (calculated from 900nm to 1200nm), compared to cells with metal back reflectors. We also conclude that the optimum thickness of the over-coating layer is dependent on the wavelength to be optimised, the angular distribution of the plasmonic nanoparticles scattering within the layer, and the type of adjacent metal reflector used. It performs best when condition for constructive interference or enhanced electric field at the rear Si interface is satisfied. An enhancement of effective optical path length factor Z of around 9-fold compared to an Al reflector is achieved by using the optimised double layer reflector, higher than the 6-fold enhancement reported previously.

Enhanced light trapping in polycrystalline silicon thin-film solar cells using plasma-etched submicron textures

In this work a highly scattering rear Si surface texture (RST) is realized by plasma etching of polycrystalline silicon (poly-Si) thin-film solar cells on glass. The resulting RST shows reflection haze values of more than 95% at the Si–air interface. The average feature size of the texture is around 200nm. We use a model based on the scalar scattering theory to calculate the scattering properties of the textured surface. We also use a commercial thin-film solar cell simulator to evaluate the light trapping and current enhancement induced by the texture. Combining this submicron RST with a micrometer-scale glass texture can produce a multi-scale rear Si surface texture. Assuming a 1900nm thick poly-Si solar cell on glass with a high-quality back surface reflector (silicon dioxide/silver stack), the calculated photon density absorbed in the poly-Si solar cell with the multi-scale rear Si surface texture corresponds to a 1-sun short-circuit current density (jsc) of 31.1mA/cm2, which is 1mA/cm2 more than the calculated jsc of a poly-Si solar cell with the same thickness on textured glass but without RST. The calculated current densities do not fu lly take current loss due to parasitic absorption into consideration, hence are slightly overestimated.