Interdigitated Back Contact Solar Cells Research Articles

Systematic Modeling and Optimization for High‐Efficiency Interdigitated Back‐Contact Crystalline Silicon Solar Cells

This study utilizes Quokka3, an advanced solar cell simulation program, specifically tailored for interdigitated back‐contact (IBC) crystalline silicon (c‐Si) solar cells. Through meticulous Quokka3 simulations, the influence of several geometric and wafer characteristics of the solar cell backside on current–voltage (I–V) performance has been scientifically explored for IBC c‐Si solar cells. The investigation encompasses parameters such as wafer thickness, bulk lifetime, resistivity, emitter and back surface field area fraction, and front‐ and rear‐surface passivation. Optimal values for these parameters have been proposed to enhance the efficiency of IBC solar cells. These recommendations contain an emitter percentage of 70%, a wafer thickness ranging from 200 μm, a wafer resistivity of 1 Ω cm, and a wafer bulk lifetime of at least 10 ms. Moreover, under conditions where the cell is not short‐circuited, the potential for achieving higher cell efficiency, up to 26.64%, has been shown.

Evaluating the Practical Efficiency Limit of Silicon Heterojunction–Interdigitated Back Contact Solar Cells by Creating Digital Twins of Silicon Heterojunction Solar Cells with Amorphous Silicon and Nanocrystalline Silicon Hole Contact Layers

Improving power conversion efficiency (PCE) in photovoltaics has driven innovative approaches in solar cell design and technology. Silicon heterojunction (SHJ) solar cells exhibit advantages in PCE due to their effective passivating contact structures. SHJ–interdigitated back contact (SHJ–IBC) solar cells have the potential to surpass traditional SHJ cells, attributed to their advantage in short‐circuit current (JSC). Herein, Silvaco Atlas technology computer‐aided design is used to create digital twins of high‐efficiency SHJ solar cells with amorphous silicon and nanocrystalline silicon hole selective contact (HSC) layers. Using parameters from digital twins of SHJ solar cells, the practical efficiency limit of SHJ–IBC solar cells is assessed. The results show that SHJ–IBC cells can achieve potential efficiencies of 27.01% with amorphous HSC and 27.38% with nanocrystalline HSC. Further efficiency augmentation to 27.51% can be achieved by narrowing the gap from 80 to 20 μm. This study not only advances comprehension of SHJ–IBC solar cells but also provides insights into optimizing geometrical configurations for improved performance. The utilization of digital twins provides a valuable tool for predicting and evaluating the performance of SHJ–IBC solar cells, contributing substantively to the ongoing development of high‐efficiency photovoltaic technology.

Structuring Interdigitated Back Contact Solar Cells Using the Enhanced Oxidation Characteristics Under Laser‐Doped Back Surface Field Regions

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%.

Design Rule of Electron- and Hole-Selective Contacts for Polycrystalline Silicon-Based Passivating Contact Solar Cells.

A crystalline silicon (c-Si) solar cell with a polycrystalline silicon/SiOx (poly-Si/SiOx) structure, incorporating both electron and hole contacts, is an attractive choice for achieving ideal carrier selectivity and serving as a fundamental component in high-efficiency perovskite/Si tandem and interdigitated back-contact solar cells. However, our understanding of the carrier transport mechanism of hole contacts remains limited owing to insufficient studies dedicated to its investigation. There is also a lack of comparative studies on the poly-Si/SiOx electron and hole contacts for ideal carrier-selective solar cells. Therefore, this study aims to address these knowledge gaps by exploring the relationship among microstructural evolution, dopant in-diffusion, and the resulting carrier transport mechanism in both the electron and hole contacts of poly-Si/SiOx solar cells. Electron (n+ poly-Si/SiOx/substrate)- and hole (p+ poly-Si/SiOx/substrate)-selective passivating contacts are subjected to thermal annealing. Changes in the passivation properties and carrier transport mechanisms of these contacts are investigated during thermal annealing at various temperatures. Notably, the results demonstrate that the passivation properties and carrier transport mechanisms are strongly influenced by the microstructural evolution of the poly-Si/SiOx layer stack and dopant in-diffusion. Furthermore, electron and hole contacts exhibit common behaviors regarding microstructural evolution and dopant in-diffusion. However, the hole contacts exhibit relatively inferior electrical properties overall, mainly because both the SiOx interface and the p+ poly-Si are found to be highly defective. Moreover, boron in the hole contacts diffuses deeper than phosphorus in the electron contacts, resulting in deteriorated carrier collection. The experimental results are also supported by device simulation. Based on these findings, design rules are suggested for both electron and hole contacts, such as using thicker SiOx and/or annealing the solar cell at a temperature not exceeding the critical annealing temperature of the hole contacts.

Stable passivation of cut edges in encapsulated n-type silicon solar cells using Nafion polymer

In this study, the edge passivation effectiveness and long-term stability of Nafion polymer in n-type interdigitated back contact (IBC) solar cells are investigated. For new module technologies such as half-cut, triple-cut, or shingled modules, cutting of the cells introduces unpassivated edges with a high recombination rate and this limits the module power. These cut edges can be “repassivated” after cutting and in this work Nafion polymer is used to achieve this. First, different edge types, namely emitter edges (n+/n/p+) and back surface field (BSF) edges (n+/n/n+), as well as different cutting techniques such as laser cut and cleave (L&C), thermal laser separation (TLS), and mechanical cleaving are evaluated. It is found that TLS and mechanical cleaving enable good repassivation on both BSF and emitter edges. Second, industrial-size IBC solar cells are made to assess the effect of the edge repassivation on performance. On 1/4-cut M2 size IBC cells with two emitter edges, efficiency is improved by over 0.3%abs. However, an efficiency improvement was not observed for similar cells with BSF edges, due to an insufficient passivation at the bulk edges. Last, the real-world stability of the Nafion repassivation is evaluated in industrially relevant module stacks by laminating the repassivated wafers with ethylvinylacetate (EVA) or polyolefin elastomer (POE) encapsulants and then exposing them to industry standard testing of 1000 h under damp heat conditions (85 °C, 85% relative humidity). The tests reveal that the repassivation is stable in EVA encapsulants but not in POE.

Interdigitated Back‐Contacted Carbon Nanotube–Silicon Solar Cells

Carbon/silicon heterojunctions provide a new perspective for silicon solar cells and in particular those made from carbon nanotubes (CNTs) have already achieved industrial‐level power conversion efficiency and device size when using organic passivation and a back‐junction design. However, the current state of the art device geometry for silicon photovoltaics is the interdigitated back contact (IBC) cell and this has yet to be demonstrated for CNT/Si solar cells due to the complexity of fabricating the required patterns. Herein, IBC‐CNT solar cells are demonstrated via the simple spin coating of a conductive hole‐selective passivating film and the evaporation of buried silicon oxide/magnesium electron‐selective contacts for both polarities. The CNT coverage area fraction (fCNT) and the gap between the two polarities are optimized to minimize electrical shading loss and ensure high photocarrier collection. Large‐area (4.76 cm2) highly efficient (17.53%) IBC‐CNT solar cells with a Voc of 651 mV and Jsc of 40.56 mA cm−2 are demonstrated and are prepared with one alignment step for the CNT/Si contact, and photolithographic‐free and room‐temperature processes. These performance parameters are among the best for solution‐processed dopant‐free IBC schemes and indicate the feasibility of using low‐dimensional carbon materials in IBC solar cells.

A Spot-Area Method to Evaluate the Incidence Angle Modifier of Photovoltaic Devices—Part 1: Cells

The angle of incidence of solar irradiation on photovoltaic modules varies throughout the day. At larger angles of incidence, the modules are subject to higher reflection losses, resulting in lower light transmission and energy yield. The impact of the relative angular transmittance on the energy yield is often evaluated with a correction factor, commonly referred to as incidence angle modifier (IAM). In this article, a new method to quantify the IAM of photovoltaic devices is presented, which is different from the methods proposed in IEC 61853-2: It encompasses a spot-area irradiation, a customized angle probe holder, and a current-to-voltage converter. This first part focuses on single-cell minimodules and validates the new method on two different cell architectures—an interdigitated back-contact solar cell and a four-busbar solar cell, with an analysis of the measurement bias due to busbars. A second part will follow on the implementation of the same method to commercial-size silicon modules. The study is intended to contribute to the IEC 61853-2 standard. A detailed uncertainty analysis is presented and the method is validated versus IEC 61853-2. Our proposed method shows great potential as it is less expensive and more adaptable than existing standard methods.

Over 700 mV IBC Solar Cell by Optimizing Front Surface Field Passivation

In this article, the front surface field (FSF) passivation of n-type interdigitated back contact (IBC) solar cell was studied and a method to improve the FSF passivation performance of n-type IBC solar cell was proposed. We optimized the phosphorus diffusion on the front surface of IBC solar cell to form a field passivation structure with low surface concentration and shallow junction depth. The surface recombination rate was calculated using EDNA2. Solar cell parameters were simulated by Quokka, and finally we did experiment verification. The results showed that when the deposition time and flow rate of POCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> in the phosphorus diffusion process time is 3 min and POCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> flow rate is 80 sccm, the front surface saturation current density (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) is reduced to 3.71 fA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , corresponding to the front surface recombination rate of 100 cm/s. On solar cells, open-circuit voltage reached 704 mV, the average conversion efficiency of IBC solar cell exceeded 24%, and the highest conversion efficiency reached 24.28%.

Solution-processed PSS:MoOx composite thin film with triple function (passivation, antireflection, and hole-selective transport) for application in IBC solar cells

A novel solution-processed organic–inorganic composite material of poly(4-styrene sulfonic acid) (PSS) and molybdenum oxide (MoOx) nanoparticles is reported for use at the front of interdigitated back contact (IBC) solar cells as a triple-function layer.

Detailed luminescence modelling in high-efficiency solar cells for precise calibration of spatially resolved characterisation methods: A bottom-up opto-electrical approach

In the scope of solar cell characterisation, spatially resolved imaging (SRI) methods (EL, PL and LBIC) have long been a standard procedure for valuable in-depth evaluation and extraction of various spatially resolved material properties, especially those related to the electrical behaviour. While this extraction can be straightforward in the case of laterally homogeneous devices, the situation is vastly different when the structural features are laterally varying, such as in the case of interdigitated back contact (IBC) solar cells. We show that in the case of laterally varying devices inherent device optical properties play a far more important role in determining the measured profile in this case and may indeed overshadow any underlying electrical effects. We therefore propose and validate a methodology that couples SRI characterisation with advanced bottom-up simulation of IBC solar cells. The method fully accounts for lateral device variability and allows for accurate extraction of the underlying electrical phenomena. We demonstrate the applicability of the method on state-of-the-art high-efficiency IBC solar cells, and explain the key factors, which could lead to misinterpretation of the results obtained solely by SRI measurements. • Interpretation of measured IBC electroluminescence profiles through opto-electrical simulation. • Decoupling of underlying optical and electrical phenomena. • Device optics overshadows recombination driven fluctuations of luminescence profiles. • Rear interface strongly influences the shape of the extracted luminescence profile. • Shape of the luminescence profile is highly dependent on imaging system’s aperture.

Mitigating Cut Losses in Interdigitated Back Contact Solar Cells

The edge recombination losses of crystalline silicon solar cells become significant when they are cut into smaller pieces to be assembled into modules. With the interdigitated pattern of doped <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$p$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula> regions on the rear side, the interdigitated back contact (IBC) solar cells can be cut through different doped regions. In this study, the cutting losses in IBC solar cells are investigated and various cutting scenarios are studied. Through simulations and experimental measurements, it is found that the cut losses can be reduced by cutting through the back surface field rather than through the emitter. The losses under low light intensity are reduced to an even greater extent. When a 23% cell is cut into 1/3 pieces, the efficiency can be increased by 1.2% <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_\mathrm{rel}$</tex-math></inline-formula> (cut related losses were improved from 2.0% <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_\mathrm{rel}$</tex-math></inline-formula> to 0.8% <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_\mathrm{rel}$</tex-math></inline-formula> ) under standard 1-sun testing conditions, compared to cutting through the emitter. Under low light intensity of 0.25 sun, the improvement is around 2.4% <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_\mathrm{rel}$</tex-math></inline-formula> . The improvement is mainly due to lower FF losses in the I–V characteristics, and this is further confirmed by Suns– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$V_{\text{oc}}$</tex-math></inline-formula> and PL measurements. In the pFF analysis, the additional losses due to laser damage are also observed. This strategy of cutting through the BSF region in IBC solar cells can be quickly adopted in mass production without the need for additional processes or equipment and both module power and energy yield can be increased.

Maskless interdigitated a-Si:H PECVD process on full M0 c-Si wafer: Homogeneity and passivation assessment

In this work, the use of a novel, large area, mask-less and contact-less patterning technique is demonstrated for the first time, showing the localized deposition of hydrogenated amorphous silicon (a-Si:H) in a desired pattern over the full surface of an M0 (156 mm × 156 mm) solar wafer. The patterning functionality is achieved through a custom-designed RF electrode possessing a series of “slits” and placed in close proximity to the substrate in a plasma enhanced chemical vapor deposition (PECVD) chamber. Under a certain set of process conditions, a plasma only ignites within these slits, and the localized plasma results in localized patterned deposition of a-Si:H with feature widths compatible with application in an interdigitated back contact (IBC) solar cell design (760 μm). The homogeneity of the finger width and thickness over the surface of the M0 wafer is evaluated, with a 37% variation in thickness (at very high deposition rate, ∼1 nm/s) but only a 4.7% variation in finger width (MSE). With this application in mind, the impact of the deposition of such “fingers” on an underlying “blanket” passivation layer is assessed. Passivation is maintained or improved up to a given finger/blanket thickness ratio, above which the passivation is degraded. It is shown that the acceptable process window contains suitable thickness values for heterojunction (HJT) IBC solar cells, and the physical processes at the origin of this phenomenological observation are discussed.

Imaging Current Paths in Silicon Photovoltaic Devices with a Quantum Diamond Microscope

Magnetic imaging with nitrogen-vacancy centers in diamond, also known as quantum diamond microscopy, has emerged as a useful technique for the spatial mapping of charge currents in solid-state devices. In this work, we investigate an application to photovoltaic (PV) devices, where the currents are induced by light. We develop a widefield nitrogen-vacancy microscope that allows independent stimulus and measurement of the PV device, and test our system on a range of prototype crystalline silicon PV devices. We first demonstrate micrometer-scale vector magnetic field imaging of custom PV devices illuminated by a focused laser spot, revealing the internal current paths in both short-circuit and open-circuit conditions. We then demonstrate time-resolved imaging of photocurrents in an interdigitated back-contact solar cell, detecting current build-up and subsequent decay near the illumination point with microsecond resolution. This work presents a versatile and accessible analysis platform that may find distinct application in research on emerging PV technologies.

Interdigitated back-contacted crystalline silicon solar cells fully manufactured with atomic layer deposited selective contacts

The interdigitated back-contacted (IBC) solar cell concept has been extensively studied for single-junction cells and more recently as a good choice for three-terminal tandem devices. In this work, carrier-selective contacts based on transition metal oxides deposited by atomic layer deposition (ALD) technique are applied to IBC c-Si(n) devices. In the first part of the study, we develop a hole-selective contact based on thin ALD vanadium oxide (V2O5) layers without using an amorphous silicon interlayer. The ALD process has been optimised, i.e. number of ALD cycles and deposition temperature, as a trade-off between surface passivation and contact resistivity. Noticeable surface passivation with recombination current densities around 100 fA/cm2, as well as reasonable contact resistivity values below 250 mΩcm2 are reached using 200 ALD V2O5 cycles deposited at a deposition temperature of 125 °C (∼10 nm layer thickness). The optimised ALD V2O5-based contact is combined with both an ALD TiO2-based electron-selective contact and an excellent surface passivation in non-contacted regions provided by ALD Al2O3 films, to form a fully ALD IBC c-Si(n) solar cell scheme. Fabricated devices yield photovoltaic efficiencies and pseudo efficiencies, i.e. calculated without series resistance losses, of 18.6% and 21.1% respectively (3 cm × 3 cm device area). These results reveal the potential of the ALD technique to deposit transition metal oxide (TMO) films as selective contacts on high efficiency devices, paving the way of using low thermal-budget, low cost and highly scalable processes for a highly demanding IBC solar cell architecture in the photovoltaic industry.

Design, realization and loss analysis of efficient low-cost large-area bifacial interdigitated-back-contact solar cells with front floating emitter

Large-area (251.96 cm 2 ) bifacial interdigitated-back-contact (IBC) solar cells are presented in this work. We employ front floating emitter (FFE) to replace the front surface field (FSF) to simplify the process sequences. A simplified process flow is exploited to fabricate the IBC solar cells through industrial equipment and compatible processes. Double side boron diffusion followed by etch-back to form the emitter and lightly doped front surface, reducing high-temperature influence on the bulk lifetime and fabrication complexity. Ion implantation and anneal process is applied for base doping. The cell conversion efficiency reaches 22.92%, independently certificated by Fraunhofer Institute for Solar Energy System CalLab (Fraunhofer ISE). The IBC solar cells feature an open metallization grid, which offers a bifacial response with the bifaciality reaches to 72%. Only one-step mask and opening procedure was used, which greatly simplified the process. These results demonstrate the feasibility of this simplified process for manufacturing low-cost high-efficiency of IBC cells. Key parameters such as surface recombination J 0 , metal contact recombination J 0-metal , contact resistivity of the cells are extracted by specially designed structures. Loss analysis shows that further efficiency improvement can be attained though reducing the contact resistance and metal contact recombination. The results in this work indicates the potential of this novel process for producing low-cost high-efficient IBC solar cells. Large-area efficient IBC solar cells are fabricated by using front floating emitter (FFE), which reducing the process complex and save cost. With the simplified process, the conversion efficiency of 22.92% and bifaciality of 72% are attained. Through special structures and patterns designing, the performance parameters ( J 0 , J 0-metal , and ρ c ) are investigated, and the losses of the IBC cell are analyzed by numerical simulation. • Large-area bifacial interdigitated back contact (IBC) solar cell are fabricated through industrial equipment. • Front floating emitter (FFE) replace of FSF reduce electrical shading effect increase the process tolerance. • Front side etch back to from FFE, ion-implantation to from BSF simplified the process of IBC cell. • Extract key parameters ( J 0 , J 0-metal , ρ c ), Quokka 3D simulator was performed to estimate the performance of solar cell. • The front efficiency is 22.92% and 16.54% on the back, the bifaciality is 72%.

Realization and simulation of interdigitated back contact silicon solar cells with dopant-free asymmetric hetero-contacts

Crystalline silicon (c-Si) solar cells using interdigitated back contact (IBC) configurations are one of the most promising candidates to reach the practical efficiency limits of c-Si solar cells. However, the complexity of the process flow hinders the mass production of the IBC cells with conventional doped regions. One of the simple fabrication methods is to introduce the dopant-free carrier-selective contacts, which utilizes the fabrication processes with low temperature, e.g., the thermal evaporation or the spin coating. In this paper, we investigated efficiency close to 20% silicon IBC solar cells with dopant-free asymmetric hetero-contacts. In this solar cell configuration, the high work function material MoOx was chosen as the hole transporting layer, while the low work function material LiF was chosen as the electron transporting layer, respectively. The simulation results indicate that the perspective efficiency exceeding 22% for this type of cells is achievable with the optimized pitch width and improved passivation quality of the contacts, which has a great potential for the industrialization of IBC solar cells with simple fabrication processes.

Oxygen‐alloyed poly‐Si passivating contacts for high‐thermal budget c‐Si heterojunction solar cells

AbstractCrystalline silicon solar cells with passivating contacts based on doped poly‐Si exhibit high optical parasitic losses. Aiming at minimizing these losses, we developed the oxygen‐alloyed poly‐Si (poly‐SiOx) as suitable material for passivating contacts. From passivation point of view, poly‐SiOx layers show excellent passivation quality and carrier selectivity for both n‐type (iVOC,flat = 740 mV, contact resistance ρc = 0.7 mΩ/cm2, iVOC,textured = 723 mV) and p‐type (iVOC,flat = 709 mV, ρc = 0.5 mΩ/cm2). Optically, due to the incorporation of oxygen, the absorption coefficient of poly‐SiOx becomes much lower than that of doped poly‐Si at long wavelength. Both n‐type and p‐type poly‐SiOx layers are concurrently deployed in front/back‐contacted (FBC) solar cells with a front indium tin oxide (ITO) layer to facilitate the lateral transport of carriers and minimize cell's reflection. A high cell FF of 83.5% obtained in double‐side flat FBC solar cell indicates an efficient carrier collection by these passivating contacts. An active‐area cell efficiency of 21.0% featuring JSC,EQE = 39.7 mA/cm2 is obtained in front‐side textured poly‐SiOx FBC cell, with the potential of further improvement in both VOC and FF. The optical advantage of poly‐SiOx over poly‐Si as passivating contact is also observed with a 19.7% interdigitated back‐contacted (IBC) solar cell endowed with poly‐SiOx emitter and back surface field. Compared to the reference 23.0% IBC solar cell with poly‐Si passivating contacts, the one based on poly‐SiOx passivating contacts shows higher IQE at wavelengths above 1100 nm. This indicates that for both FBC and IBC cells, poly‐SiOx passivating contacts hold potential in enhancing the cell JSC by maximizing the cell spectral response.

Mathematical modelling of a novel heterojunction SIS front surface and interdigitated back-contact solar cell

In this paper, we propose the design and fabrication of a novel heterojunction semiconductor–insulator–semiconductor (SIS) front surface and interdigitated back-contact (IBC) solar cell. We approximate the performance parameters and loss analysis of the proposed solar cell using MATLAB software programming. Many studies have reported the experimental analysis of amorphous silicon (a-Si) IBC solar cells. A number of silicon heterojunction solar cell designs with promising efficiency have been reported in the past few decades. In this study, a long-lifetime (~ 2 ms) n-Si substrate was considered so that a sufficient number of photogenerated carriers could reach the interdigitated layer and be absorbed. The availability of carriers at the interdigitated back surface was further enhanced by considering a high-low junction created by a ZnO n+ layer at the front surface. A very thin layer of thermally deposited insulator SiO2 was considered between the ZnO and n-Si. This layer reduces the detrimental effects of interface defects. This is the first study in which we have theoretically investigated an IBC solar cell using metal oxide semiconductor layer deposition, thereby avoiding the expensive and complicated doping and diffusion process. In general, a high-concentration n+ layer is doped to create a high-low junction at the front to accelerate the transport of carriers to the back junctions. We propose a cost-effective method using thermal deposition of a SiO2 layer followed by sol–gel ZnO layer deposition, which serves the same purpose as an n+ layer by introducing an SIS junction potential at the front. The interdigitated back surface was designed with sequential n+ a-Si and p+ a-Si vertical junctions.

Photo-generation profiles in deeply-etched, two-dimensional patterns in interdigitated back contact solar cells

Interdigitated back contact (IBC) crystalline silicon solar cell model has been developed by using SILVACO in order to achieve design optimization in non-conventional device configurations. The SILVACO software was employed to evaluate performance of IBC solar cell as a function of texture while keeping identical semiconductor process parameters including doping of emitter, BSF and FSF. Based on the period of the pyramidal texturing, the textured surface can be distributed uniformly throughout the solar cell as exhibited by the 40-μm period pattern for which the incident is uniformly and deeply penetrated inside the IBC solar cell. Therefore, efficiency of the IBC solar cell is boosted to 23.31% in comparison with 22.36% from planar IBC solar cell. The photo-generation profile for planar surface is not uniformly and deeply distributed throughout the IBC solar cell but for P40D20 the distribution of incident photons well distributed and penetrates deeper into IBC solar cell which leads to improved IBC solar cell performance. For IBC solar cells with periods larger than 40 μm, performance is degraded due to formation of shadows within the solar cell located at grooves of pyramid. These shadows effectively reduce number of photons and therefore degrade solar cell performance. Hence, the texturization process can boost solar cell performance only if appropriate parameters are chosen otherwise reduced performance can result due to enhanced shadow effects inside the solar cell even though the front surface has no metallic contacts to physically block light.

Characteristics and development of interdigital back contact solar cells

Silicon-based solar cells are an important field for the development of the photovoltaic industry. The grid electrode on the front surface of the traditional silicon solar cell causes shading loss. However, the positive and negative electrodes are placed on the back surface of the interdigitated back contact(IBC) solar cell, which causes no shading loss and improvement of photoelectric conversion efficiency. The core of the IBC silicon solar cell is the interface control, field effect control and the design of the positive and negative electrode patterns on the back. Different manufacturing processes ensure the accuracy of the grid electrode and reduce production costs. This paper systematically introduces the structure and interface characteristics and development history of IBC solar cells, and looks forward to the development trend and application prospects of IBC solar cells.