Interdigitated Back Contact Research Articles

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.

Design of Large Poly‐Si on Oxide Interdigitated Back Contact (POLO IBC) Silicon Solar Cells with Local Al–p+ Contacts in the Constraints of Measurement and Module Integration

Interdigitated back contact (IBC) silicon solar cells with a passivating n‐type poly‐Si on oxide emitter and an aluminum‐doped p+ base contact on M2‐sized Ga‐doped p‐type Cz wafers are reported. The Al‐doped base contact forms during the firing of the printed contacts and allows for a lean process flow. The device optimization balances recombination at the base contacts against resistive losses and respects constraints set by the need of interconnecting cells in a module and contacting the cells temporally by a measurement chuck. A special sample holder is designed for measuring the Isc–Voc curve of the IBC cell with a busbar‐less metal grid. The pseudo‐efficiency is 24.7%. All fingers of each polarity are connected with wires and an efficiency of 22.3% is measured. The comparison of simulations and measurements reveals that the cell has 23.4% efficiency without the series resistance losses due to the wires. A huge part of the resistive losses in the cell are the transport losses of the majorities in the base dissipating a power that corresponds to 0.76%abs efficiency and the resistive losses at the Al‐doped base contact (0.29%abs).

UV‐induced degradation of high‐efficiency silicon PV modules with different cell architectures

AbstractDegradation from ultraviolet (UV) radiation has become prevalent in the front of solar cells due to the introduction of UV‐transmitting encapsulants in photovoltaic (PV) module construction. Here, we examine UV‐induced degradation (UVID) in various commercial, unencapsulated crystalline silicon cell technologies, including bifacial silicon heterojunction (HJ), interdigitated back contact (IBC), passivated emitter and rear contact (PERC), and passivated emitter rear totally diffused (PERT) solar cells. We performed UV exposure tests using UVA‐340 fluorescent lamps at 1.24 W·m−2 (at 340 nm) and 45°C through 4.02 MJ·m−2 (2000 h). Our results showed that modern cell architectures are more vulnerable to UVID, leading to a significant power decrease (−3.6% on average; −11.8% maximum) compared with the conventional aluminum back surface field (Al‐BSF) cells (<−1% on average). The power degradation is largely caused by the decrease in short‐circuit current and open‐circuit voltage. A greater power decrease is observed in bifacial cells with rear‐side exposure compared with those with front‐side exposure, indicating that the rear side is more susceptible to UV damage. Secondary ion mass spectroscopy (SIMS) confirmed an increase in hydrogen concentration near the Si/passivation interface in HJ and IBC cells after UV exposure; the excess of hydrogen could result in hydrogen‐induced degradation and subsequently cause higher recombination losses. Additionally, surface oxidation and hot‐carrier damage were identified in PERT cells. Using a spectral‐based analysis, we obtained an acceleration factor of 5× between unpackaged cells (containing a silicon nitride antireflective coating on the front) in the UV test and an encapsulated module (with the front glass and encapsulant blocking 90% of the UV at 294 nm and 353 nm, respectively) in outdoor conditions. From the analytical calculations, we show that a UV‐blocking encapsulant can reduce UV transmission in the module by an additional factor of ~50.

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.

50-µm thick flexible dopant-free interdigitated-back-contact silicon heterojunction solar cells with front MoOx coatings for efficient antireflection and passivation

We demonstrate experimentally a flexible crystalline silicon (c-Si) solar cell (SC) based on dopant-free interdigitated back contacts (IBCs) with thickness of merely 50 µm for, to the best of our knowledge, the first time. A MoOx thin film is proposed to cover the front surface and the power conversion efficiency (PCE) is boosted to over triple that of the uncoated SC. Compared with the four-time thicker SC, our thin SC is still over 77% efficient. Systematic studies show the front MoOx film functions for both antireflection and passivation, contributing to the excellent performance. A double-interlayer (instead of a previously-reported single interlayer) is identified at the MoOx/c-Si interface, leading to efficient chemical passivation. Meanwhile, due to the large workfunction difference, underneath the interface a strong built-in electric field is generated, which intensifies the electric field over the entire c-Si active layer, especially in the 50-µm thick layer. Photocarriers are expelled quickly to the back contacts with less recombined and more extracted. Besides, our thin IBC SC is highly flexible. When bent to a radius of 6 mm, its PCE is still 76.6% of that of the unbent cell. Fabricated with low-temperature and doping-free processes, our thin SCs are promising as cost-effective, light-weight and flexible power sources.

Solar Cells with Laser Doped Boron Layers from Atmospheric Pressure Chemical Vapor Deposition

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.

Optical management for back-contact perovskite solar cells with diverse structure designs

Interdigitated back-contact (IBC) structure design is a promising alternative to further promote the optical absorption and the power conversion efficiency of perovskite solar cells (PSCs). However, their full potential has not been reached owing to the absence of the advanced structure designs and a lack of a deep understanding on the related physics mechanism. In this paper, we proposed three typical IBC configurations featuring flat perovskite layer, textured electron transport layer (ETL) and hole transport layer (HTL), and textured HTL but flat ETL. By the numerical simulations, the optical properties of the three related designs are investigated systematically. The simulation results reveal that anti-reflection coating (ARC) thickness plays an important in determining the device performance and the optimal ARC thickness is suggested to be 70–80 nm. The optimal structure sizes are confirmed by optimizing the structure parameters. In addition, the light-trapping mechanism is clarified by the position-determined photocurrent density and the spatial electric field distributions. Moreover, dependence of optical response under the various perovskite thickness is checked, suggesting that textured IBC structure design is good to achieve high optical absorption. The simulation results demonstrated in this paper provide a valuable guide to design IBC PSCs with high optical performance.

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%.

N-type doping of SiC-passivated Ge by pulsed laser melting towards the development of interdigitated back contact thermophotovoltaic devices

In this article, a method for phosphorous (n-type) doping of germanium based on spin-on dopant sources and Pulsed Laser Melting (PLM) throughout an amorphous silicon carbide (a-SixC1-x:H) layer, which provides both surface passivation and electrical isolation, has been demonstrated, paving the way towards the development of Ge-based interdigitated back contact thermophotovoltaic devices. This method offers simultaneous opening of the a-SixC1-x:H layer and creation of a heavily doped region underneath without using photolithographic steps, eventually enabling a low-cost and scalable manufacturing process. This article focuses on the optimization of the n+/p junction formation by studying the effect of different laser energy fluences and number of pulses on the diffusion profiles measured by secondary ion mass spectrometry, and on the electrical performance characterized by Van der Pauw-Hall technique. Additionally, the crystalline quality after PLM has been analyzed by Rutherford backscattering measurements in channeling conditions, high-resolution X-Ray diffraction and transmission electron microscopy. High level of donor activation (up to 1·1019 cm−3), low sheet resistance (≈50 Ω/□), and high mobility (275–700 cm2/V·s) have been obtained, with a weaker dependency of these parameters on the explored laser energy fluence range. A prototype diode has been developed demonstrating a rectifying behavior but with high saturation current densities. Point-like contact formation will be implemented in future works to reduce the laser irradiated area, and thus, improve the surface passivation and device characteristics.

Highly Efficient and Industrially Feasible Interdigitated Back‐Contact Perovskite Solar Cells with Front Carrier Transport Layers Selected Using 2D Simulation

Interdigitated back‐contact (IBC) perovskite solar cells (PSCs) have great potential for highly efficient and low‐cost solar energy conversion. However, their full potential has not been achieved. In particular, there is no practically available front surface and rear contact design for IBC‐PSCs as for the conventional crystalline silicon IBCs, which propose challenges in realizing high efficiency. Herein, innovative quasi‐interdigitated back‐contact (QIBC) PSC designs that enhance the effective lateral transport of carriers are proposed and therefore a realistic wide pitch for back contacting in the range of hundreds of micrometers is allowed. The novel design features implementing an appropriate conductive and well‐passivated carrier transport layer, referred to as a front‐carrier transport layer (FCTL), on the front surface of the QIBC‐PSC. Technology computer‐aided design optical/device simulations are used to investigate the function of the FCTL in increasing the cell performance and achieve 23.23% of power conversion efficiency (PCE) after FCTL design optimizations for a QIBC‐PSC with a rear contact pitch of 200 μm. Further improvement of the PCE over 25% can be potentially achievable by improving the film and passivation quality. This work opens up a new approach to fabricate realistic highly efficient IBC‐PSCs.

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.

Inkjet-Printed In Situ Structured and Doped Polysilicon on Oxide Junctions

We investigate the inkjet printing of liquid silicon ink to form in situ doped and structured passivating contacts. The ink consists of neopentasilane oligomers in solvents and decomposes into amorphous silicon with a short anneal. By printing boron- and phosphorus-doped ink on silicon oxide, polycrystalline silicon on oxide (POLO) junctions for both p-type and n-type polarities (POLO <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) are formed and the saturation current densities as low as 5 fA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> are achieved for n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -POLO junctions. We perform a structured printing in interdigitated back contact (IBC) geometry achieving emitter and base fingers with an average finger height of up to 103 nm. The application of inkjet printing allows for a simplification of POLO and POLO <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> solar cell processing. In particular, for POLO <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> -IBC cells, a lean process flow is facilitated.

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.

Passivating Polysilicon Recombination Junctions for Crystalline Silicon Solar Cells

Polysilicon recombination junctions whose n‐type bottom layers double as a passivating contact to the silicon surface are investigated. Such recombination junctions are a key element in the interconnection of tandem devices with a silicon bottom cell, and they could be used to simplify the processing sequence of single‐junction cells with interdigitated back contacts (IBCs). Polysilicon tunneling junctions require high processing temperatures to crystallize the layers; however, this also facilitates interdiffusion of dopants, whereas tunnelling relies on degenerate doping concentrations in the constituent layers and sharp interfaces between them. Using secondary‐ion mass spectrometry (SIMS) in dynamic mode, it is found that dopants diffuse readily across the interface, thus compromising the junction. The undesired diffusion is suppressed by modifying the interface with C, O, or a combination of these. Moreover, it is found that the modification does not interfere with diffusion of H, an essential element to passivate defects at the surface of the silicon wafer. Thus, implied open‐circuit voltages (iV oc) of up to 740 mV are demonstrated for contact resistivities less than 40 mΩ cm2.

Admittance spectra of silicon photocells in dark mode

An extended model of silicon photovoltaic cells with localized parameters is presented, including inductance in a series branch. Based on the recorded admittance-frequency spectra, the dependences of the active and reactive components from the bias voltage for PERC (Passivated Emitter Rear Cell), HIT (Heterojunction with Intrinsic Thin-layer solar cells) and IBC (Interdigitated Back Contact cells) elements are reconstructed. The structure of the Nyquist diagrams for the components of admittance spectra is analyzed, which make it possible to visually determine the working scheme of the chain based on the elementary links of the first and second orders.

Low-Resistance Hole Contact Stacks for Interdigitated Rear-Contact Silicon Heterojunction Solar Cells

Achieving low contact resistivity for the p-contact in silicon heterojunction (SHJ) solar cells is challenging when classic n-type transparent conductive oxides (TCOs), such as indium tin oxide (ITO), are used in the contact stack. Here, we report on SHJ solar cells with interdigitated back-contact (IBC) and a direct aluminum (Al) metallization applied to the p-contact. We find that carefully annealing an Al/a-Si:H(p) (p-type amorphous silicon) contact at moderate temperatures leads to a specific contact resistivity that is half as low as its silver (Ag)/ITO counterpart. This is explained by Al diffusing into a-Si:H(p) upon temperature treatment, forming a partially crystallized aluminum silicide layer. For a sufficiently high doping level in a-Si:H(p), this enables an efficient tunnel-recombination of holes from a-Si:H(p) to the Al contact. An estimate for this tunneling-dominated specific contact resistivity is calculated as a function of the interface doping density. Best fabricated IBC SHJ solar cells with Al p-contact yield a fill factor of 77.5% and a power conversion efficiency of 22.3%. The main differences to devices with an Ag/ITO/a-Si:H(p) contact stack are a decrease in open-circuit voltage by 14 mV and a slightly higher series resistance ( R s). While the first aspect can be ascribed to increased interface recombination, the second one is unexpected and requires further investigation. Interestingly, omitting an intermediate TCO does not lead to current losses in devices with Al contacts, which is further investigated by optical simulations. Finally, electrical equivalent circuit simulations are conducted to describe the electrical behavior of the investigated devices.

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.

Influence of light illumination on the potential-induced degradation of n-type interdigitated back-contact crystalline Si photovoltaic modules

We investigate the potential-induced degradation (PID) of n-type interdigitated back-contact (IBC) crystalline Si (c-Si) photovoltaic (PV) modules under a negative bias stress and the influence of light illumination on the PID. IBC PV modules show PID characterized by a reduction in the short-circuit current density (J sc) and open-circuit voltage (V oc) under negative bias stress, while no fill factor (FF) reduction is observed. The degradation may originate from the introduction of sodium (Na) into c-Si and the resulting enhancement of carrier recombination on the surfaces of the IBC cells. Light illumination of 1 sun during the negative bias PID test results in less severe reductions of J sc and V oc. A reduction in the electric field on the surface Si nitride (SiN x ) film, due to carrier generation in the SiN x and the resulting increase in its conductivity, is a possible explanation for the mitigation of the Na-related PID.

Three‐dimensional multi‐ribbon interconnection for back‐contact solar cells

AbstractBack‐contact solar cells are an interesting technology with advantages over traditional two‐sided cells. A lack of standardized and low‐cost interconnection methods inhibits their market penetration. In an attempt to overcome this obstacle, this work introduces an interconnection technology, based on a fabric of encapsulant with incorporated metal ribbons. The encapsulant is tailored for this application by adding glass fibres to a thermoplastic polyolefin. For this tailored encapsulant, characterization experiments were conducted and results on viscosity and coefficient of thermal expansion are shown. Initial reliability testing on sample‐size modules with high‐efficiency interdigitated back‐contact (IBC) cells shows promising results, passing up to four times the IEC 61215 standard for thermal cycling.