Search

The current–voltage measurement is the most important measurement in solar cell quality control. As the contacting process of cells results in mechanical stress and consumes a significant amount of measurement time, this work presents an IV characterization based on contactless measurements only. An empirical model is introduced that can derive the full IV curve and IV parameters as the open‐circuit voltage, short‐circuit current density, fill factor, and efficiency. As a basis, a series of photoluminescence and contactless electroluminescence images and spectral reflectance measurements are used. An advantage of the model's convolutional neural network design lies in the semantic compression of local image structures across the input data. Within an ablation study, it is shown that the empirical model is well suited to combine these data sources, which is the optimal input configuration for contactless IV derivation. The accuracy, e.g., with an error in efficiency of 0.035%abs and correlation of over 99%, is similar to comparing two contacting IV measurement devices. The contactless IV curves also have a close fit to their contacted counterparts. Within simulations on module level, it is demonstrated that contactless binning performs as well as contacting binning and does not result in any additional mismatch loss. [ABSTRACT FROM AUTHOR]

Low‐cost and high‐efficiency tandem solar cells are promising candidates for a future industrial mass production. Nowadays, the passivated emitter and rear cell (PERC) technology makes up the major market share; therefore, it is an attractive option to use the PERC technology as bottom cell concept for a perovskite–silicon tandem device. Long‐term optimization of the PERC technology led to highly efficient, low‐cost, and mature devices. For PERC‐like bottom cells, mainly an adapted front‐side design is needed: Design constrains of a PERC single junction are relaxed to some extent, because such an updated PERC bottom cell only needs to absorb long wavelength photons, transports about half the current and, in a monolithic tandem, lateral transport, and the use of firing‐through local silver contacts is not a mandatory prerequisite. Consequently, to make PERC suitable for tandem application, a systematic reevaluation of the current PERC technology is performed here considering five different front‐side concepts. We investigate locally contacted and full‐area transparent conducting oxide (TCO)‐based interconnection concepts for PERC, as well as the full‐area tunnel oxide passivating contact (TOPCon). Our simulation work elaborates on the advantages and physical constrains of each concept and gives guidelines for the optimization of the phosphorus diffused emitter and front interconnection layers. We conclude that both full‐area and locally contacted front‐side concepts are promising candidates for achieving tandem cell efficiencies of about 30%. In this work we focus on how to make the mainstream silicon solar cell technology – namely the passivated emitter and rear cell (PERC) – suitable as bottom cell in a perovskite‐silicon tandem device. A detailed optical and electrical simulation model incoporating the parasitic absorption losses and (tunneling) transport at the different bottom cell front side concepts (including passivating contact schemes like TOPCon) was elaborated in Sentaurus TCAD which enables to predict the tandem effi-ciency poten-tial of several PERC‐like bottom cells. [ABSTRACT FROM AUTHOR]

We present an analytical model for the internal resistance of passivated emitter and rear totally diffused (PERT) solar cells. First, we apply the model of Saint-Cast for the spreading resistance of a passivated emitter and rear cell (PERC) structure with line-shaped contacts. To account for the additional vertical current flow through the silicon wafer and the lateral current flow through the back surface field of a PERT structure, we add a parallel current path using common analytical expressions. We compare the analytical models with two-dimensional numerical simulations based on Quokka 3 and find deviations of less than 6% for the internal resistance. In addition, we compare the analytical model of the internal resistance of PERC and PERT solar cells with experimental data of the series resistance of PERC and PERT solar cells. [ABSTRACT FROM AUTHOR]

Herein, boron‐doped cast‐monocrystalline silicon wafers that have been fabricated using the Seed Manipulation for ARtificially controlled defect Technique (SMART mono‐Si) are examined. Their suitability for passivated emitter and rear cell (PERC) fabrication is investigated. Applying a zero busbar layout energy conversion efficiencies of η = 21.9% for SMART mono‐Si, η = 22.2% for gallium‐doped Cz‐Si (Cz‐Si:Ga), and η = 22.3% for boron‐doped Cz‐Si (Cz‐Si:B) are achieved at similar doping levels between 0.7 Ω cm ≤ ρB ≤ 1.0 Ω cm. Therefore, SMART mono‐Si PERCs show almost the same performance as Cz‐Si PERCs. Apart from the performance of SMART mono‐Si PERCs, the minority charge carrier bulk lifetime τB of the SMART mono‐Si wafers after different high‐temperature process steps in the PERC process flow is investigated. After emitter formation, this analysis confirms the high material quality of SMART mono‐Si yielding τB ≈ 1.3 ms at an injection level of Δn = 1015 cm−3. The bulk lifetime after firing is similar to the level determined for mCz‐Si:B and Cz‐Si:Ga reference wafers of similar doping level. [ABSTRACT FROM AUTHOR]

Herein, a method for advanced series resistance imaging via electroluminescence (EL) for silicon solar cells is presented. The well‐known method by Haunschild et al. is revisited. The Fuyuki assumption of a linear relation between diffusion length and EL signal is shown to be not applicable to silicon devices nowadays due to larger minority charge carrier diffusion lengths and thinner solar cells. A new relation derived by Breitenstein is used here instead. The updated method for series resistance and saturation current imaging based on two EL images, which show a far superior separation of contrast and almost 60% shorter data acquisition times in comparison with the original method by Haunschild, is presented. The Weber contrast of the unwanted signal caused by recombination in resistance image is reduced from 0.89 to 0.44, using the advanced method for a prominent feature on the sample cell. The contrast due to resistance stays at the same level. The dark saturation current density images show 20% higher peaks at recombination active areas and also a 5% low. [ABSTRACT FROM AUTHOR]

A method for analyzing the power losses of solar cells is presented, supplying a complete balance of the incident power, the optical, thermodynamic, and electrical power losses and the electrical output power. The involved quantities have the dimension of a power density (units: W/m2), which permits their direct comparison. In order to avoid the over-representation of losses arising from the ultraviolet part of the solar spectrum, a method for the analysis of the electrical free energy losses is extended to include optical losses. This extended analysis does not focus on the incident solar power of, e.g., 1000 W/m2 and does not explicitly include the thermalization losses and losses due to the generation of entropy. Instead, the usable power, i.e., the free energy or electro-chemical potential of the electron-hole pairs is set as reference value, thereby, overcoming the ambiguities of the power balance. Both methods, the power balance and the free energy loss analysis, are carried out exemplarily for a monocrystalline p-type silicon metal wrap through solar cell with passivated emitter and rear (MWT-PERC) based on optical and electrical measurements and numerical modeling. The methods give interesting insights in photovoltaic (PV) energy conversion, provide quantitative analyses of all loss mechanisms, and supply the basis for the systematic technological improvement of the device. [ABSTRACT FROM AUTHOR]

Current studies reveal the expectation that photovoltaic (PV) energy conversion will become the front-runner technology to stem against the extent of global warming by the middle of this century. In 2019, the passivated emitter and rear cell (PERC) design has taken over the majority of global photovoltaic solar cell production. The objective of this paper is to review the fundamental physics of the underlying cell architecture, its development over the past few decades to an industry main stream product, as well as an in-depth characterization of current cells and the future potential of the device structure. The early development of PERCs was set by an intriguing series of improvements starting in 1989 and resulting in a long-standing energy conversion efficiency record of 25.0% set up in 1999. It took a decade of intense technological development to implement this structure as an upgrade to existing production lines and another decade to increase the efficiency of industrially manufactured cells to over 22%. Our analysis of state-of-the-art large-area screen-printed PERCs is based on the pilot-line technology in the Photovoltaic Technology Evaluation Center at the Fraunhofer ISE, which is assumed to be representative of current state-of-the art cell processing. The main recent cell efficiency improvements have been achieved thanks to fine line metallization taking advantage of the high quality emitter formation and passivation and to improvements in material quality. In order to enhance the energy yield of the PV modules, innovations in interconnection technology like multibusbar and shingling technology as well as bifaciality are supported by PERC developments. Over the years, ongoing improvements have been made in the understanding of PERCs by analytical and numerical modeling of these devices. We show a study based on 3D numerical modeling and an extrapolation of the PERC device structure and technology to achieve an efficiency of 26%. This result surpasses earlier investigations due to the combination of technology components, as further improved front contact and emitter design as well as rear passivation and mirrors. We expect that PERCs can also play a strong role at the bottom of multijunction solar cells and will defend a strong position in global PV production beyond the end of the now starting decade. [ABSTRACT FROM AUTHOR]

We present a paper about vignetting in the context of luminescence imaging of solar cells and wafers. The physical phenomenon vignetting and its contributions are reviewed. A simple model to simulate vignetting and a method of measuring the vignette by the variation of aperture are introduced. The simulated and the measured results are compared showing good agreement with less than 2.1% deviation. For the investigated luminescence setup, it is shown that vignetting can cause an intensity decrease of up to 20% toward the image corners for wide opened apertures. To quantify the correction quality, a correction quality factor is adopted from a recent publication and applied to the suggested method. Additionally, the correction quality is quantified by investigating the linear correlation between luminescence intensity and charge carrier product measured via photoconductance on a suitably prepared sample. The correlation coefficient increases from R2 = 0.92 to R2 = 0.95 after the correction. [ABSTRACT FROM AUTHOR]

The loss analysis of state-of-the-art p-type Czochralski-grown silicon passivated emitter and rear solar cells (PERC) fabricated in a manner close to industrial production is presented in this paper. The 6-inch solar cells are featuring a homogeneous emitter on the front side, an Al2O3 passivation layer and local contacts on the rear side. The peak energy conversion efficiencies obtained are 21.1% for a standard antireflection coating (ARC) and 21.4% for a double-layer ARC. The loss analysis is based on an extended characterization of the solar cells and of special samples, which allow the separation of the contributions of each region of the solar cell including metallization. Their impact is determined experimentally on the open-circuit voltage, the short-circuit current density, and the fill factor. Based on the measurements, the devices are numerically simulated. The free energy losses are analyzed using the simulation model. Based on the results from the loss analysis, it is found that the integration of a selective emitter structure and the further improvement of the rear surface would allow for efficiencies above 22% in the short term. [ABSTRACT FROM AUTHOR]

The measurement of the current-voltage (IV) characteristics is the most important step for quality control and optimization of the fabrication process in research and industrial production of crystalline silicon solar cells. We propose a methodology to determine the IV characteristics of silicon solar cells in a contactless way. We summarize the theory behind the method, describe the experimental setup and prove the validity of the concept by comparing contactless with conventionally measured IV results. We demonstrate that the differences in open-circuit voltage, short-circuit current, fill factor, and efficiency are smaller than 2.5 % rel for a test set consisting of four passivated emitter and rear cells (PERC cells), two tunnel oxide passivated contact (TOPCon) cells and a silicon heterojunction (SHJ) cell. The methodology eliminates mechanical stress on the solar cells and the time required for contacting the cells, does not require broad busbars for contacting and, hence, enables to reduce the silver consumption, simplifies the measurements of shingle cells and potentially shortens the required time, avoids shading by the contact units and consumable costs for the probes, and yields additional information (reflectance spectrum, quantum efficiency) on the cells compared to conventional IV testing. The methodology might facilitate further applications in the future, e.g., contactless outdoor testing of modules, individual diagnosis of failed cells within a module, and on-the-fly IV measurements of cells. [Display omitted] • A contactless method for current-voltage testing of silicon solar cells is proposed. • It may reduce cell breakage and costs. • It may improve line throughput and light homogeneity and gives extra information. • The method combines four contactless measurement techniques. • The proof of principle of the method is successfully demonstrated for 3 cell types. [ABSTRACT FROM AUTHOR]

Bifacial solar modules are expected to increase their market share in the coming years. To date, most bifacial cells in production and under research are realized on n-type silicon substrates. However, p-type silicon has been dominating photovoltaic industry, partly due to its lower cost. In this work, we present an approach to combine bifacial applications with the industrial p-type passivated emitter and rear (PERC) structure: a bifacial PERC cell (biPERC). Simulation results are presented that showcase a high potential for bifacial gains of the biPERC cell. First experimental results of the biPERC concept on large-area multicrystalline silicon substrates yield a monofacial efficiency of 17.8%. The biPERC cell, therefore, is an easy-to-apply modification to a PERC route and enables higher output powers due to bifacial applicability. [ABSTRACT FROM AUTHOR]

In back-contact solar cells, both external polarities are located at the back surface of the device, which allows for higher photocurrent generation on cell level and reduced series resistance on module level, leading to higher energy conversion efficiencies compared to conventional solar cells and modules. However, the majority charge carriers, which are generated near the back emitter, have to flow laterally e.g. through the base in order to reach the external majority carrier contact. In the present work, we analyse the lateral series resistance by means of measurement and simulation for high-performance metal wrap through (HIP-MWT) solar cells. We compare theoretical models and experimental methods to extract the effective series resistance from simulated and measured current–voltage characteristics and show that lateral voltage variations significantly increase the local recombination current. If the width of the gap between the external majority carrier contacts is reduced from the typical value of 3.5mm to ideally 0mm, we expect an increase of the energy conversion efficiency of approximately 0.1%abs. for cells with three continuous rear emitter contacts on 125mm×125mm large silicon wafers. In a simulation study, the bulk doping concentration N A and the bulk lifetime are varied yielding an optimal base resistivity of 0.6Ωcm–1.5Ωcm for HIP-MWT solar cells based on Czochralski-grown silicon in the degraded state of the boron–oxygen defect and an optimal resistivity of less than 1.0 Ω cm for the case of bulk lifetimes larger than ~300µs. [ABSTRACT FROM AUTHOR]

The BOSCO solar cell represents a bifacial structure with double-sided collection. The structure allows the use of standard module interconnection technology and favours the use of material with low to medium diffusion length and low resistivity for maximum benefit towards other structures, such as Al-BSF and PERC. Within this work, we present first results on different multicrystalline silicon materials yielding a monofacial efficiency of 17.4% on large-area wafers from block-cast mc-Si. This value represents a gain of ∼0.7%abs compared to Al-BSF cells processed in parallel. The applicability for bifacial operation is demonstrated by a significantly increased quantum efficiency for rear side illumination. These results make the BOSCO solar cell concept a promising candidate to further boost the output of utility-scale PV plants even when using low-cost wafers of low to medium diffusion length material. [ABSTRACT FROM AUTHOR]

Free carrier absorption (FCA) is a parasitic absorption process in highly doped silicon that might significantly reduce the amount of photons, potentially generating electron-hole pairs. Existing FCA parameterizations are mostly setup by evaluating absorption data in the range \lambda\geq 4~\mum. If applied in the wavelength range \lambda=1.0\--2.0~\mum, including the relevant range for silicon solar cells, most parameterizations are not appropriate to describe FCA accurately. In this paper, new parameters are presented using optical simulation on the base of experimental reflection data to enhance the quantification of FCA losses in the considered wavelength range. [ABSTRACT FROM AUTHOR]

One drawback of passivating contacts in crystalline silicon solar cells is the current loss due to parasitic absorption within the involved material layers. When employed on an illuminated side of the cell, the full spectrum of the incident light will be partly absorbed before reaching the silicon bulk. Additionally, near-infrared (NIR) absorption can substantially reduce the cell's NIR spectral response (SR) also when employed on the non-illuminated side. As those losses are hard to measure directly, optical modeling is crucial for their quantification. This paper presents an extension to an analytical light-trapping model to account for parasitic absorption in the near-surface region via a new parameter A ppp (absorbed fraction per perpendicular pass). We test the model by analyzing i) reflectance measurements on samples with varying doping profiles, ii) SR measurements on TOPCon solar cells with varying back-side poly-silicon layers, and iii) SR measurements of a bifacial silicon heterojunction cell. We show that the model can well be calibrated by fitting a single value for A ppp to reflectance measurements. This enables a quantification of the parasitic absorption loss without requiring knowledge of all layer's optical properties. The model also is able to predict parasitic absorption in TOPCon cells when knowing the thickness and doping density of the poly-Si layer. Having proven the usefulness of A ppp to represent parasitic absorption as a single-valued quantity, we suggest A ppp as a third figure of merit for the quality of a passivating contact, next to the recombination parameter J 0c and the contact resistivity ρ c. • New parameter A ppp quantifies near-surface parasitic absorption in a c-Si solar cell. • A ppp extends an existing analytical light-trapping model. • Model can be fitted to reflectance to quantify parasitic absorption current loss. • Proposed as third figure of merit for a passivating contact besides J 0c and ρ c. [ABSTRACT FROM AUTHOR]

With this work, we introduce numeric three-dimensional simulation of metal spiking into highly boron-doped surfaces of n-type silicon solar cells, which is moreover performed with a simulation of the quasi-steady-state photoconductance technique. This setup serves as a virtual experiment to simulate the dark saturation current density j 0,met of metallized boron-doped emitters with respect to metal spikes originating from the silver–aluminum (Ag–Al) contact. With the results obtained from this simulation model we approach quality and quantity of increased j 0,met and give detailed insight to which degree a solar cell’s performance is possibly harmed by this effect. We show that metal spikes penetrating into boron-doped emitters are of harmless nature concerning j 0,met until their tips reach depths where boron doping concentration is lower than approximately 10 18 cm −3 . Deeper spikes then lead to an exponential increase in j 0,met as more and more carriers from emitter and also the base are able to diffuse to its tip and recombine there. With the help of j 0 -results obtained experimentally in combination with the simulation results, we discuss the influence of spikes on emitter recombination, the benefits that can be achieved with deeper emitter doping profiles, and suggestions for the further development of pastes to contact boron-doped surfaces. [ABSTRACT FROM AUTHOR]

Abstract We present a novel method to analyze the local current-voltage I - V characteristics of both solar cells and cell precursors. The method, which we call "Suns-ILIT", is based on illuminated lock-in thermography (ILIT) measurements and photoluminescence imaging (PLI) in open-circuit conditions with varying illumination intensities. Compared to conventional techniques for the determination of local solar cell parameters, the advantage of Suns-ILIT lies in the high accuracy while imposing minimal requirements on the sample. In particular, no electrical contact to the sample is needed. We derive the necessary equations from the contributions to the power dissipation and investigate the impact of the Peltier heating and cooling on the final outcome. The method is applied to a standard multicrystalline silicon PERC solar cell for demonstration. Highlights • We introduce a method to obtain spatially resolved information on the I-V characteristics of solar cells and precursors. • To this end, a combination of illuminated lock-in thermography and photoluminescence imaging is used. • The theory behind the method is explained in detail. • The method is demonstrated on a multicrystalline silicon PERC solar cell and compared to conventional methods. • The method does not need any electrical contacts and it allows for the I-V measurement of sub-cells in tandem devices. [ABSTRACT FROM AUTHOR]

For measuring the current-voltage (I–V) characteristics of busbarless solar cells, there is a certain degree of freedom in the choice of the contacting configuration as none has been defined as standard yet. This leads to the question of how the energy conversion efficiency of a busbarless solar cell should be specified when there are different measured values for it and poses the risk of misinterpreting cell measurements: Designing the measurement system for highest cell efficiencies for example may be tempting but can lead to cell results disassociated from later module performance and reduced cell-to-module power factors. The loss in module efficiency can thereby significantly exceed 5 % rel. It is therefore recommended to always adapt the contacting system to the module interconnection to yield meaningful I–V results in cell measurements. As a remedy for non-adapted measurement conditions, it is shown that I–V results can be converted from various cell measurement configurations to the module configuration. An analytical approach for the conversion of I–V results between measurement systems with different numbers of current contact bars as well as different shading properties is proposed. The approach is validated experimentally on busbarless cells over a large grid resistivity range. For three measurement systems with very different contacting schemes, the differences in fill factor and efficiency between the systems before correction clearly exceeded 10 % rel for high grid resistivities. After correction, good agreement in I–V characteristics within typical measurement uncertainties were shown. Limitations to the analytical approach associated with finger interruptions are identified and discussed. • Study on impact of contacting system on current-voltage characteristics of busbarless solar cells. • Improper contacting systems can lead to increased cell-to-module losses and misdirected cell optimization. • Contacting system should match module interconnection scheme for meaningful cell results. • Proposal and evaluation of correction procedure for conversion of cell results. [ABSTRACT FROM AUTHOR]

Abstract: Aerosol jet printing is investigated as a new deposition method for a current collecting grid in indium tin oxide (ITO) free organic solar cells with an inverted layer sequence. In this device configuration, the ITO layer which usually serves as the hole contact is replaced by a transparent highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer in combination with a silver grid deposited by aerosol jet printing. Since the cells are illuminated from the grid side, the optimisation of the grid design is a trade-off between area coverage and conductivity of the grid lines. These factors have been controlled by the printing parameters such as chuck temperature, printing speed and the number of printing passes. In this paper, we demonstrate that continuous, conductive grid lines with a minimum line width of can be processed on the top of the PEDOT:PSS layer. For single pass printing the area coverage varied from 5.8% to 11.9% with corresponding effective sheet resistances ranging from to . The ITO-free inverted devices with aerosol jet printed grid (an active area of 1.1cm2) show comparable performance to the cells with an evaporated gold grid. The effective sheet resistance can be further decreased by multiple printing passes without increasing the area coverage proportionally due to an improved aspect ratio. By increasing the conductivity and aspect ratio by multiple line printing, the cell length in the module structures can be significantly extended. [Copyright &y& Elsevier]