HIT Solar Cells Research Articles

Influence of the semiconductor/metal rear contact on the performance of n(a-Si:H)/i(a-Si:H)/p(c-Si) heterojunction solar cells

The aim of this work is to analyze on the results of using of Al/Ag layer as a rear contact to improve the performance of heterojunction silicon solar cells. An analytical method is presented to extract the physical parameters of the equivalent circuit. These parameters are extracted to simulate the I(V) characteristic of heterojunction silicon solar cells, with Al and Al/Ag rear-metal contact. A good agreement between our analytical method and experimental measurement of electrical characteristics is obtained which show clearly how the Al/Ag rear contact can improve the characteristics of silicon solar cells. The influence of the rear-metal contact on the performance of the c-Si(p)-based bifacial HIT solar cell, i.e., the ZnO/Al/a-Si:H(n)/a-Si:H(i)/c-Si(p)/metal solar cell, is investigated in detail by computer simulation using the AFORS-HET software. Accordingly, the design optimization of the bifacial HIT solar cells on c-Si(p) substrates is provided. These simulation show an optimal conversion efficiency of 23% when the rear-metal contact is perfectly ohmic.

A High-Efficiency HIT Solar Cell With Pillar Texturing

To investigate the effect of surface texturing for high-efficiency heterojunction with intrinsic thin layer (HIT) solar cells, we have systematically designed different textures and numerically evaluated their ability to trap light. These evaluations were first calibrated by physically fabricating a general pyramid-structured HIT solar cell. The performance of various textures is compared, such as a flat structure, a pillar structure, and different types of pyramid and inverse pyramid structures. Simulation results identify the pillar structure as the best, because the light is reflected several times onto the surface, so that more of the light is trapped by the substrate. The pillar structure HIT solar cell's conversion efficiency of 25.73% is an improvement over the 24.7% of the conventional random pyramid HIT solar cell.

Design and Optimization of Amorphous Based on Highly Efficient HIT Solar Cell

The objective of this paper is to improve the power conversion efficiency of HIT solar cell using amorphous materials. A high efficiency amorphous material based on two dimensional heterojunction solar cell with thin intrinsic layer is designed and simulated at the research level using Synopsys/RSOFT-Solar Cell utility. The HIT structure composed of TCO/a-Si:H(p)/a-Si:H(i)/c-Si(n)/a-Si:H(i)/a-Si:H(n+)/Ag is created by using of RSOFT CAD. Optical characterization of the cell is performed by Diffract MOD model based on RCWA (rigorous coupled wave analysis) algorithm. Electrical characterization of the cell is done by Solar cell utility using based on Ideal diode method. In addition, optimization of the different layer thickness in the HIT structure is executed to improve the absorption and thereby the photocurrent density. The proposed HIT solar cell structure resulted in an open circuit voltage of 0.751 V, a short circuit current density of 36.37 mA/cm2 and fill factor of 85.37% contributing to the total power conversion efficiency of 25.91% under AM1.5G. Simulation results showed that the power conversion efficiency is improved by 1.21% as compared to the reference HIT solar cell. This improvement in high efficiency is due to reduction of resistive losses, recombination losses at the hetero junction interface between intrinsic a-Si and c-Si, and optimization of the thicknesses in a-Si and c-Si layers.

Enhanced efficiency in bifacial HIT solar cells by gradient doping with AFORS-HET simulation

The paper presents a systematical simulation study of the influence of gradient doping of both emitter and back surface field layer on the photovoltaic (PV) performances of TCO/a-Si:H(p)/a-Si:H(i)/c-Si(n)/a-Si:H(n+)/TCO/Ag bifacial structure heterojunction with intrinsic thin layer (HIT) solar cells using AFORS-HET software simulation package. The gradient doping instead of uniform doping for emitter can promote the PV performance due to the presence of an additional electric field coming from the gradient doping, while the gradient doping of back surface field layer has negligible effect or negative influence on the cell performance compared to uniform doping, which can be explained by the varied energy band diagrams near the back junction interface. A final efficiency of 25.75% has been realized by using gradient doping of emitter with the same total doping amount as that of uniform doping case and uniform doping of back surface field layer for n-type bifacial HIT solar cells. This study can offer guidance on how to improve HIT solar cell efficiency beyond the world record value in experiment and how to achieve higher efficiency in mass production of HIT solar cells.

HIT Solar Cells with N-Type Low-Cost Metallurgical Si

A conversion efficiency of 20.23% of heterojunction with intrinsic thin layer (HIT) solar cell on 156 mm × 156 mm metallurgical Si wafer has been obtained. Applying AFORS-HET software simulation, HIT solar cell with metallurgical Si was investigated with regard to impurity concentration, compensation level, and their impacts on cell performance. It is known that a small amount of impurity in metallurgical Si materials is not harmful to solar cell properties.

NUMERICAL SIMULATION OF THERMAL BEHAVIOR AND OPTIMIZATION OF a-Si/a-Si/C-Si/a-Si/A-Si HIT SOLAR CELL AT HIGH TEMPERATURES

Purpose. Silicon heterostructure solar cells, particularly Heterojunction with Intrinsic Thin layer (HIT) cells, are of recommended silicon cells in recent years that are simply fabricated at low processing temperature and have high optical and temperature stability and better efficiency than homojunction solar cells. In this paper, at first a relatively accurate computational model is suggested for more precise calculation of the thermal behavior of such cells. In this model, the thermal dependency of many parameters such as mobility, thermal velocity of carriers, band gap, Urbach energy of band tails, electron affinity, relative permittivity, and effective density of states in the valence and conduction bands are considered for all semiconductor layers. The thermal behavior of HIT solar cells in the range of 25-75 °C is studied by using of this model. The effect of the thickness of different layers of HIT cell on its external parameters has been investigated in this temperature range, and finally the optimal thicknesses of HIT solar cell layers to use in wide temperature range are proposed .

High Mechanical Strength Thin HIT Solar Cells With Graphene Back Contact

It is widely known that thinner Si substrate is the main path for lower $/Watt HIT solar cells due to improved charge collection, reduced bulk and total recombination, and fewer raw material consumption (Panasonic, IEEE Journal of Photovoltaics., vol. 4, p. 96, 2014). Nonetheless, thin substrates always lead to low mechanical stability and wafer breaking. In this work, spray coated 50 nm graphene layer is used as the back electrode in Si HIT solar cells to enhance the mechanical stability. With the incorporation of graphene as the back electrode in Si HIT solar cells, remarkable improvements in substrate mechanical strength are achieved. Without the degradation of HIT solar cell efficiency, hardness is increased nearly twofold from 902 to 1747 HV. The Young's modulus is increased from 93.9 to 140.1 GPa while the ultimate tensile strength is increased from 96.71 to 273.68 MPa. Low-cost chemical exfoliation method and low-temperature (150 °C) spray coating method have been employed for the preparation and deposition of thin graphene back electrode, respectively. In addition, unlike the graphene as the substitute for ITO in OLED applications, the graphene strengthened thin silicon substrate technology here imposes no additional constraint on the graphene electrode transparency since it is used as a back electrode. We, thereby, believe that our proposed method is effective for attaining higher efficiency and lower $/Watt thin Si HIT solar cell technology with enhanced mechanical strength.

Investigation of Nanoscale Quasi Pyramid Texture for HIT Solar Cells Using n-type High Performance Multicrystalline Silicon

In this work, an n-type high performance multicrystalline silicon (nHPMC) ingot (τ >1.2 ms) was cast at NTNU. A new method to manufacture nHPMC solar cells with hetero junction solar cell architecture is presented. Texturing of the wafers is performed through silver assisted chemical etching followed by an alkaline solution treatment process. The slight differences of the reactions between the concentration of the alkali solutions and the nanopores on silicon surface has been determined and used to tailor different textures. Alkaline solutions with gradient concentration were developed to improve the surface morphology for HIT solar cells after a silver assisted chemical etching process. A homogeneous texture with quasi pyramid morphology was then obtained through balancing the reflectance and surface properties on nHPMC wafers. This kind of quasi pyramid texture is also a good starting point for the surface passivation during HIT processes. An efficiency of 19.03% has been obtained, demonstrating the potential of using n-type HPMC in the production of cost effective solar cells.

Single‐Side Heterojunction Solar Cell with Microcrystalline Silicon Oxide Emitter and Diffused Back Surface Field

The goal of high efficiency in Si solar cells has been developed to a close limit by Si heterojunction (SHJ) scheme. The further work should aim to simplify its fabrication process for the reduction of cost. In this study, a scheme single‐side heterojunction solar cell with hydrogenated microcrystalline silicon oxide emitter ((µc‐SiOx:H(p+)) and diffused back surface field (BSF) was presented, to save the flip of wafers and the number of vacuum chambers. The device performance evolution was performed by AFORS‐HET simulation and experiments. It is demonstrated that FF of the solar cell is improved using diffused BSF to replace the intrinsic and doped stack hydrogenated amorphous silicon (a‐Si:H(n+/i)) layer in HIT solar cell, but Jsc and Voc decreased. The former ascribes to the better conductivity of diffused BSF and band offset free in homojunction, the later the free carrier absorption in diffused region and the removal of rear a‐Si:H passivation layer. Further, the introduction of µc‐SiOx:H(p+) emitter can compensate for the loss of Jsc above and increase FF, again, due to its wide band gap and high electrical conductivity, leading to a device performance similar to routine HIT device. This work provides a candidate for the roadmap of SHJ solar cells.

Simulation optimizing of n-type HIT solar cells with AFORS-HET

This paper presents a study of heterojunction with intrinsic thin layer (HIT) solar cells based on n-type silicon substrates by a simulation software AFORS-HET. We have studied the influence of thickness, band gap of intrinsic layer and defect densities of every interface. Details in mechanisms are elaborated as well. The results show that the optimized efficiency reaches more than 23% which may give proper suggestions to practical preparation for HIT solar cells industry.

Superior silicon surface passivation in HIT solar cells by optimizing a-SiOx:H thin films: A compact intrinsic passivation layer

Abstract The microstructure of the intrinsic amorphous silicon oxide (i-a-SiO x :H) thin films is the key for crystalline silicon surface passivation in high-performance HIT solar cells. Understanding and subsequently optimizing the i-a-SiO x :H microstructure is essential in improving defect passivation and carrier transportation in a-SiO x :H films. In this work, we investigate the relationship between the bulk microstructure of i-a-SiO x :H thin films at different oxygen content and the passivation quality of the silicon surface. The results revealed that, as the oxygen content increases, the dominating growth mechanism of i-a-SiO x :H films changes. Consequently, the component contents of i-a-SiO x :H thin films were varied and the microstructure showed a first improved and then deteriorated trend with increasing oxygen content. A compact, less-defective and ordered microstructure of the a-SiO x :H film can only be obtained when there comes a tradeoff between Si O and Si H(Si 3 ) bonding formation. Correspondingly, the improved defect passivation and the enhanced carrier transportation in a-SiO x :H films lead to the increase of V oc , FF and QE of HIT solar cells, all of which are key solar cell performance parameters.

HIT Solar Cell With V20x Window Layer

ABSTRACTIn the conventional crystalline silicon heterojunction solar cell with the intrinsic thin layer structure (the HIT solar cell), a p-doped thin film silicon or its alloy (pDTF-Si/A) is used as the hole collecting window layer. However, the parasitic absorbance in the pDTF-Si/A window layer, and the toxic, explosive diborane gas used for p-doping are limiting factors for achieving HIT cells with reduced processing costs and / or higher efficiencies. In this work, pDTF-Si/A is replaced by V2Ox, which is deposited by a simple physical vapor deposition technique. Due to the wide band gap of V2Ox, the HIT solar cell with the V2Ox window layer generates a higher short-circuit current density than the reference conventional HIT cell under 1 sun, and achieves an open-circuit voltage of 0.7 V. Furthermore, the charge carrier lifetime and pseudo-efficiency values of the HIT solar cell with the V2Ox window layer indicate that this cell has the potential to outperform the conventional HIT cell in terms of the power conversation efficiency under the standard test conditions.

Improvement of the recombination and infrared light losses by rear surface chemical polishing in silicon heterojunction solar cells

Rear surface chemical polishing (RSCP) was investigated for the improvement of the internal reflection and surface passivation of heterojunction solar cells with intrinsic thin layers (HIT). The HIT solar cells without or with RSCP treatment were prepared by plasma-enhanced chemical vapor deposition and physical vapor deposition techniques. Scanning electron microscopy results showed that rounding of the spires and V-groove bottom of the pyramid as well as smoothing of incline surface of the pyramid were achieved. These effects would decrease the loss of infrared light transmittance and interface recombination at the rear surface of the cells. To experimentally corroborate these two points, two special geometries, ITO/c-Si/hydrogenated amorphous silicon (a-Si:H)/ITO and a-Si:H/c-Si/a-Si:H, were introduced as a test of the reflectance/transmittance spectra and the minority carrier lifetime. Weakened transmittance and enhanced lifetime were observed for the sample with RSCP, which are responsible for the improvement of J sc and V oc, respectively. Therefore, RSCP is a promising candidate for improving the performance of HIT solar cells.

Interface states study of intrinsic amorphous silicon for crystalline silicon surface passivation in HIT solar cell**Project supported by the National Natural Science Foundation of China (Grant Nos. 51361022 and 61574072) and the Postdoctoral Science Foundation of Jiangxi Province, China (Grant No. 2015KY12).

Intrinsic hydrogenated amorphous silicon (a-Si:H) film is deposited on n-type crystalline silicon (c-Si) wafer by hot-wire chemical vapor deposition (HWCVD) to analyze the amorphous/crystalline heterointerface passivation properties. The minority carrier lifetime of symmetric heterostructure is measured by using Sinton Consulting WCT-120 lifetime tester system, and a simple method of determining the interface state density from lifetime measurement is proposed. The interface state density measurement is also performed by using deep-level transient spectroscopy (DLTS) to prove the validity of the simple method. The microstructures and hydrogen bonding configurations of a-Si:H films with different hydrogen dilutions are investigated by using spectroscopic ellipsometry (SE) and Fourier transform infrared spectroscopy (FTIR) respectively. Lower values of interface state density are obtained by using a-Si:H film with more uniform, compact microstructures and fewer bulk defects on crystalline silicon deposited by HWCVD.

Simulation and Optimization Characteristic of Novel MoS<sub>2</sub>/c-Si HIT Solar Cell

Monolayer MoS2 has excellent optoelectronic properties, which is a potential material for solar cell. Though MoS2/c-Si heterojunction solar cell has been researched by many groups, little study of MoS2/c-Si solar cell physics is reported. In this paper, MoS2/c-Si heterojunction solar cells have been designed and optimized by AFORS-HET simulation program. The various factors affecting the performance of the cells were studied in details using TCO/n-type MoS2/i-layer/p-type c-Si/BSF/Al structure. Due to the important role of intrinsic layer in HIT solar cell, the effect of different intrinsic layers including a-Si:H, nc-Si:H, a-SiGe:H, on the performance of TCO/n-type MoS2/i-layer/p-type c-Si/Al cell, was studied in this paper. The results show that the TCO/n-type MoS2/i-layer/p-type c-Si/Al cell has the highest efficiency with a-SiGe:H as intrinsic layer, efficiency up to 21.85%. The back surface field effects on the properties of solar cells were studied with p + μc-Si and Al as BSF layers. And the effect of various factors such as thickness and band gap of intrinsic layer, thickness of MoS2, density of defect state and the energy band offset of MoS2/c-Si interface of TCO/n-type MoS2/i-layer nc-Si:H/p-type c-Si/Al cells, on the characteristics of solar cells, have been discussed for this kind of MoS2 heterojunction cells. The optimal solar cell with structure of TCO/n-type MoS2/i-type nc-Si:H/p-type c-Si/BSF/Al, has the best efficiency of 27.22%.

Influence of patterning the TCO layer on the series resistance of thin film HIT solar cells

Thin HIT solar cells combine efficient surface passivation and high open circuit voltage leading to high conversion efficiencies. They require a TCO layer in order to ease carriers transfer to the top surface fingers. This Transparent Conductive Oxide layer induces parasitic absorption in the low wavelength range of the solar spectrum that limits the maximum short circuit current. In case of thin film HIT solar cells, the front surface is patterned in order to increase the effective life time of photons in the active material, and the TCO layer is often deposited with a conformal way leading to additional material on the sidewalls of the patterns. In this article, we propose an alternative scheme with a local etching of both the TCO and the front a-Si:H layers in order to reduce the parasitic absorption. We study how the local resistivity of the TCO evolves as a function of the patterns, and demonstrate how the increase of the series resistance can be compensated in order to increase the conversion efficiency.

Influence of Characteristic Energies and Charge Carriers Mobility on the Performance of a HIT Solar Cell

Influence of Characteristic Energies and Charge Carriers Mobility on the Performance of a HIT Solar Cell

Influence of defect states and fixed charges located at the a-Si:H/c-Si interface on the performance of HIT solar cells

In this work, a simulation study of various HIT solar cell structures was carried out using AFORS-HET simulation software. The effect of defect states and fixed charges at the a-Si:H/p-Si interface on the solar cell performance was investigated. We found that the defect states located at the upper side of the a-Si:H/p-c-Si interface affected the HIT performance more greatly than those located at the bottom side of the a-Si:H/p-c-Si interface. However, compared with interface defect states, interface fixed charges located on both sides of the c-Si wafer had an opposite effect. The crucial role of strong band bending in the crystalline part of the a-Si:H/c-p-Si interface was shown through the variation of interface defect states and interface fixed charges. By optimizing the densities of interface defect states and interface fixed charges, an efficiency of 29.19% was achieved.

Deposition of Intrinsic a-Si:H by ECR-CVD to Passivate the Crystalline Silicon Heterointerface in HIT Solar Cells

We have deposited intrinsic amorphous silicon (a-Si:H) using the electron cyclotron resonance (ECR) chemical vapor deposition technique in order to analyze the a-Si:H/c-Si heterointerface and assess the possible application in heterojunction with intrinsic thin layer (HIT) solar cells. Physical characterization of the deposited films shows that the hydrogen content is in the 15–30% range, depending on deposition temperature. The optical bandgap value is always comprised within the range 1.9–2.2 eV. Minority carrier lifetime measurements performed on the heterostructures reach high values up to 1.3 ms, indicating a well-passivated a-Si:H/c-Si heterointerface for deposition temperatures as low as 100 oC. In addition, we prove that the metal–oxide–semiconductor conductance method to obtain interface trap distribution can be applied to the a-Si:H/c-Si heterointerface, since the intrinsic a-Si:H layer behaves as an insulator at low or negative bias. Values for the minimum of D it as low as 8 × 1010 cm-2⋅eV-1 were obtained for our samples, pointing to good surface passivation properties of ECR-deposited a-Si:H for HIT solar cell applications.

Electrical Characterization of Amorphous Silicon MIS-Based Structures for HIT Solar Cell Applications.

A complete electrical characterization of hydrogenated amorphous silicon layers (a-Si:H) deposited on crystalline silicon (c-Si) substrates by electron cyclotron resonance chemical vapor deposition (ECR-CVD) was carried out. These structures are of interest for photovoltaic applications. Different growth temperatures between 30 and 200 °C were used. A rapid thermal annealing in forming gas atmosphere at 200 °C during 10 min was applied after the metallization process. The evolution of interfacial state density with the deposition temperature indicates a better interface passivation at higher growth temperatures. However, in these cases, an important contribution of slow states is detected as well. Thus, using intermediate growth temperatures (100–150 °C) might be the best choice.