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Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined, and new entries since January 2020 are reviewed.

Within the EURAMET ENG55 “PhotoClass” project, several characteristics of photovoltaic (PV) devices beyond their performance at Standard Test Conditions were investigated, including measurements at varying irradiance and temperature. Four groups of PV devices of different size and technology were prepared and corresponding round-robins were run between partner laboratories with substantially different facilities and methods – namely based on spectral or integral measurements. This paper presents the outcome of the four inter-laboratory comparisons dealing with temperature coefficient measurements of the short-circuit current of PV devices, from reference-cell size to full-size commercial modules of mainly several c-Si technologies, but also with some examples of CIGS and GaAs devices. The measurement results are compared via En number assessment, hence including measurement uncertainties. The main outcome of this measurement exercise is a very good agreement of all the laboratories although completely different approaches were applied. In some cases, laboratory measurement uncertainties are even considered rather conservative and could therefore be revised. Furthermore, a comparison between bare cells and commercial modules of the same technology is made, which may represent useful information for PV manufacturers.

In this paper we present a new update to PC1Dmod, which extends the original PC1D program by implementing Fermi-Dirac statistics and a range of state-of-the-art models in order to improve the accuracy of c-Si device simulation. In PC1Dmod 6.2 the list of models is further expanded to include a parameterization of incomplete ionization of dopants (Altermatt et al., J. Appl. Phys.100, 113715, 2006), with parameters for phosphorus, boron, arsenic, gallium and aluminum. The results have been verified against a previous implementation of the model. We show that the inclusion of incomplete ionization is of particular importance for moderately doped surface regions with doping densities in the range ∼5 × 10 17 to ∼5×10 19 cm -3 , resulting in a deviation of up to 15% in the simulated recombination current density and sheet resistance. The effect of incomplete ionization is also shown to be more pronounced in devices made from compensated Si material. Furthermore, the default solar spectrum has also been updated in PC1Dmod 6.2, taking advantage of the increased maximum file size to include a more realistic representation. The generation profiles calculated using PC1Dmod 6.2 together with input from OPAL 2 agree well with results from Sentaurus TCAD for both planar and pyramidally textured surfaces, thus facilitating a more direct comparison between PC1Dmod 6.2 and other simulation programs utilizing standard spectra. The simulation comparison is also extended to the electrical performance of the modeled devices, showing good agreement in the calculated short-circuit current density for a range of planar and textured solar cells with varying emitter doping. Finally, several new output options, including emitter saturation current and injection-dependent lifetime curves have been added, enabling a simpler and more direct way for users to access and plot important device properties.

We investigate the origin of the apparently reduced recombination parameter J 0 of highly doped regions obtained from e.g. QSSPC lifetime measurements at high injection densities as well as the influence of recombination at bulk defects on the recently updated J 0 -analysis of QSSPC measurements in the Sinton lifetime tester software. Using the example of crystalline silicon, we show that the frequently observed reduction and underestimation of J 0 , which is strongly pronounced at high injection levels, originate from neglecting the finite carrier diffusion coefficient. This work presents an analysis taking into account the finite carrier diffusion coefficient and thus enabling to evaluate charge carrier lifetime data at high injection levels leading to strongly increased consistency of the determined J 0 . Furthermore, we give a simple correction term for the recently published analysis leading to a total independence of a reasonably injection-independent Shockley–Read–Hall (SRH)-lifetime in the substrate. Combining the proposed methods, the determination of J 0 from numerically simulated lifetime-data is accurate within 3% of the input J 0 =100 fA/cm 2 over an injection range of 10 14 –3·10 16 cm −3 . The application of the proposed method to measured data of crystalline silicon devices is in excellent agreement with the simulations and shows a strongly improved linearity and thus constant extracted J 0 compared to the former and recently published methods, which underestimate J 0 at high injection levels, nearly independently from doping type and -level of the substrate. The new and simple method is implemented in a spreadsheet calculator enabling fast and robust data evaluation similar to the Sinton lifetime tester software.

The upgrade of state of the art p-type silicon solar cell production lines to passivated rear side technology (PERC) will be one of the major trends in the next years and new production processes for further cost reduction will continuously gain relevance. In 2007, we have introduced the laser based foil metallization technology “FolMet”: the rear electrode of p-type PERC devices as well as the local contact is fabricated by attaching conventional aluminum foil during the so-called laser fired contact process to the silicon wafer. This process features improved internal optical properties, a huge cost saving potential and a simplified cell production process. In this publication we focus on the acceleration of the laser process, which is together with module assembly issues a remaining challenge towards industrialization. We carried out comprehensive simulations, to better understand the correlation between different laser parameters on melting- and evaporation depth of the 8 μm thin aluminum foil. We determined lower limits for crucial laser pulse parameters to successfully attach the foil onto the substrate and validated these parameters experimentally. According to these results, we set up a system based on a pulsed high power laser featuring repetition rates Frep ≤ 2 MHz with an unique ultrafast polygon scanning system, allowing for scan-speeds vscan ≤ 1000 m/s. Thereby, we demonstrate processing times tpro < 0.8 s for industrial wafer, which corresponds to a reduction in laser process time by the factor of 20 compared to state of the art laser scanning technology.

For the extraction of spatially resolved solar cell parameters, a variety of methods has been introduced in the past years. Nearly all methods use the fact that the local luminescence intensity can be calibrated to local junction voltage. The different methods however use different approaches for the calibration. In this work we discuss the different approaches used throughout literature. We investigate the key assumption of two approaches which assumes that there are no lateral junction voltage gradients at sufficiently low excitation conditions. Our investigation is based on circuit simulations and experimental results on an example cell. We give an explanation for the remaining contrasts in luminescence images taken at these low excitation conditions. A third approach which does not rely on the key assumption is discussed with respect to measurement time in comparison to the other approaches. Finally the role of the short circuit current is discussed and a modification to the approach as known from literature is proposed.

The BOSCO (“ BO th S ides CO llecting and CO ntacted”) solar cell features a double-sided emitter and contact grids on both surfaces. The emitter region on the rear is connected to the front side by diffused vias. The structure allows the use of standard module interconnection technology and favours the use of silicon substrates 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 summarize the latest results on multi-crystalline silicon (mc-Si). Monofacial efficiencies of 17.4% on large-area wafers from 9N (99.9999999% pure) block-cast mc-Si and 16.9% for low-quality 5N upgraded metallurgical-grade mc-Si have been achieved. These values represent a gain of 0.6 to 0.7% abs compared to Al-BSF cells processed in parallel. First tests of bifacial operation under outdoor conditions yield a gain in output power of 13% compared to monofacial operation. This effect makes the BOSCO solar cell concept a promising candidate to enable bifacial operation, even for low-cost wafers of low to medium diffusion length material.

In this paper we present a one-dimensional numerical simulation study concerning the electrical properties of the TCO / a-Si:H(p) / a-Si:H(i) / c-Si(n) hole contact in amorphous / crystalline silicon heterojunction (SHJ) solar cells. Simulations where performed with Sentaurus TCAD from Synopsys considering the implemented barrier tunneling model. The modification of the a-Si:H(p) / a-Si:H(i) / c-Si(n) p/n junction by the opposing TCO / a-Si:H(p) junction and its influence on the device recombination for the relevant working conditions are investigated. We demonstrate the relevance of the effective screening length in the amorphous silicon, which depends on the effective space-charge in the a-Si:H(p) and the work function mismatch at the TCO / a-Si:H(p) interface. We highlight the importance of an improved work function matching as this presents an additional degree of freedom for the design of the SHJ and is an important parameter to reach both a very high Voc and FF.

Carrier mobility in silicon plays a crucial role for photovoltaic applications. While the influence of doping on mobility in standard monocrystalline silicon is well understood, recent research has been focused on the effects of crystal defects in multicrystalline (mc) silicon and of the presence of both acceptors and donors in compensated silicon, both introducing additional scattering centers influencing carrier mobility. In this work measurements of the majority carrier mobility have been carried out in two blocks of compensated multicrystalline silicon. Confirming existing results we come to the conclusion that with increasing compensation level mobilities may be significantly lower than predicted by Klaassen's mobility model, which is basically suited for the description of mobilities in compensated silicon as it accounts for scattering on both acceptors and donors. However, as this model is based on mobility data from uncompensated silicon, a compensation-related reduction of screening is not taken into account sufficiently. To describe mobilities in compensated silicon, a modification of Klaassen's mobility model based on published mobility data in compensated silicon is suggested.

Thermal silicon oxides are known to very effectively passivate silicon surfaces. Choosing a water vapor ambient instead of a dry oxygen atmosphere increases the oxidation rate by about one order of magnitude and considerably reduces process time and costs. State of the art pyrox systems produce steam by pyrolysis of hydrogen and oxygen gas. A new approach is the purification of vaporized deionized (DI) water. In this work we present a direct comparison of both steam generation systems, which are connected to the same quartz tube of an industrial high quality tube furnace. The higher steam saturation of the direct steam process enhances the growth rate by about 20% compared to a pyrolytic steam based process. On low-resistivity p-type substrates, excellent surface recombination velocities of around 25 cm/s are found for both systems after a forming gas anneal. Detailed characterization shows similar physical properties of the oxide layers grown by either steam from pyrol ysis or purified steam. Moreover, thermal oxide rear surface passivated silicon solar cells show similar high efficiencies exceeding 18.0% irrespective of the applied steam generation technology.

Simple analytical and statistical models for the evaluation of the temperature of PV-modules from climatic data (ambient temperature, global solar irradiation, and wind speed) are investigated. The parameters which describe the effects of cell technology and module design were evaluated from outdoor exposure data at different climatic regions. The models were validated by comparison of the simulated module temperatures with measured module temperatures at different test sites. A simplified way to determine a Realistic Nominal Module Temperature (ROMT) instead of the Nominal Operating Cell Temperature (NOCT) is proposed.

Reliable process control or predictions of solar cell efficiencies from minority carrier lifetimes on silicon wafers require precise lifetime measurements. For inhomogeneous material quality this implies the necessity of adequately averaged spatially resolved lifetime measurements. Materials such as, e.g. multicrystalline upgraded metallurgical grade silicon frequently feature relatively low lifetimes, high trap densities, and several material parameters (charge carrier mobilities and net dopant concentration) that are not straightforwardly predictable or measurable. As this may substantially compromise conventional lifetime measurements, we present a solely luminescence based lifetime imaging technique, which requires virtually no a priori information about material parameters. Our approach is based on a calibration of a wafer's photoluminescence image through a precise lifetime determination of a part of this wafer via quasi-steady-state photoluminescence. Carrier mobilities, net dopant concentration, and surface morphology leave the determination of lifetime virtually unaffected, the injection dependence of lifetime is properly taken into account, and lifetimes down to the timescale of a microsecond can be reliably measured.

Spatially resolved determination of solar cell parameters is beneficial for loss analysis and optimization of conversion efficiency. One key parameter that has been challenging to access by an imaging technique on solar cell level is short-circuit current density. This work discusses the robustness of a recently suggested approach to determine short-circuit current density spatially resolved based on a series of lock-in thermography images and options for a simplified image acquisition procedure. For an accurate result, one or two emissivity-corrected illuminated lock-in thermography images and one dark lock-in thermography image have to be recorded. The dark lock-in thermography image can be omitted if local shunts are negligible. Furthermore, it is shown that omitting the correction of lock-in thermography images for local emissivity variations only leads to minor distortions for standard silicon solar cells. Hence, adequate acquisition of one image only is sufficient to generate a meaningful map of short-circuit current density. Beyond that, this work illustrates the underlying physics of the recently proposed method and demonstrates its robustness concerning varying excitation conditions and locally increased series resistance. Experimentally gained short-circuit current density images are validated for monochromatic illumination in comparison to the reference method of light-beam induced current.

In this study we present an advanced method for precise modeling of highly aluminum-doped p+ silicon, leading to excellent agreement of numerical and experimental data within a broad range. We analyze the influence of different recombination mechanisms on the saturation current densities of Al-doped Si surfaces for different Al profiles. Lateral doping inhomogeneities and the effect of incomplete ionization have been examined in detail. We demonstrate that incomplete ionization affects the profile characteristics significantly and, therefore, has to be accounted for in accurate modeling of highly Al-doped silicon.

Significant improvements in the experimental setup of Micro-Raman (μRS) and Micro-Photoluminescence-Spectroscopy (μPL) for solar cell characterization are reported. The lateral resolution of doping density mapping with μRS is improved to below 200 nm. A highly resolved measurement on an aluminum BSF demonstrates the increase in resolution. Furthermore, the characterization of thin silicon layers within the same experimental setup is presented. An excitation source with low penetration depth is used to screen out background signal from the substrate. Finally, a surface topography mapping technique is implemented to extend μRS and μPL to uneven surfaces. With this extension micro cracks in conventionally textured silicon solar cells could be successfully characterized.

Due to boron being present in compensated n-type silicon, minority carrier lifetime degrades under illumination. Lifetime reduction by light-induced degradation up to a factor of 16 was observed for illumination with 100 mW/cm2. In contrast to p-type, the degradation process in n-type does not follow a simple exponential trend. So this degradation process is time dependently investigated in this contribution. It is known that this process depends on a combination of light intensity and sample temperature, hence degradation is investigated independently and a separation of the influences was possible: a relation between light intensity and saturation value of normalized Cz defect concentration Nt*, and between sample temperature during illumination and defect generation rate will be presented. Furthermore it is shown that due to degradation the diffusion length of compensated n-type silicon in the degraded state is as low as in degraded p-type silicon. Finally it is shown that solar cells made from a compensated n-type crystal suffer from efficiency degradation.

Recently, several novel methods have been proposed to image short-circuit current density j sc based on diverse physical principles. This work compares these methods and points out physical limitations, advantages and drawbacks of each approach. One method based on photoluminescence (PL) imaging and two methods based on dark and illuminated lock-in thermography (DLIT / ILIT) are discussed. As a versatile reference technique for j sc mapping, spectrally-resolved light-beam induced current (SR-LBIC) is applied. Experimental results for crystalline silicon solar cells with varying substrate properties, rear-side passivation schemes and process-induced defects are presented. Investigated parameters are quantitative accuracy of local j sc , spatial resolution, measurement time, spectral excitation dependency and calibration. Furthermore, robustness towards locally increased series resistance R s and injection-dependent recombination is discussed along with proneness to artefacts due to local shunts, spatially varying optics and photogeneration, and fitting algorithm artefacts.

Annealing induced silicidation of plated nickel contacts can severly lower the solar cell performance due to deep nickel silicide spikes penetrating the space charge region. This work summarizes several attempts to characterize performance limiting deep silicide structures and determines the influence of different passivation layer structuring technologies on the silicide growth. Reverse biased electroluminescence measurements revealed that the deep nickel silicides occur after an anneal and arelocated along the structured and plated passivation layer openings. Cross-section studies of the plated contacts demonstrated that deep silicide growth is present independently of the applied passivation layer structuring technology. While for laser-ablation the critical silicide structures could be mostly attributed to accelerated silicide growth at laser induced defects, there are also deep silicide structures that appear without any obvious correlation even in the case of defect free wet chemical passivation structuring of the contact openings. By varying the emitter doping profile and the annealing temperature after plating the distance of the space charge region and the surface was found to influence the annealing-induced solar cell performance decrease. Considering the presented results there are three ways to overcome annealing induced degradation of Ni plated solar cells. Either optimized process designs with sufficient contact adhesion and contact resistivity without the need of thermal silicide formation, improved silicide depth control (e.g. Ni source limited growth) or the implementation of a selective emitter design with pn-junction depths well above 1 μm within the contacted area.

This work investigates the influence of physical parameters and of different methods on the analysis of QSSPC measurements with the aim to extract J 0 -values of diffused surfaces. We show that the right choice of not only the parameter-set and physical models but also the method is crucial. The comparison with injection dependent simulation data leads to a deviation of up to 34 % from the absolute J 0 -value for parameters found in literature. In contrast, the recently implemented method in the WCT-120 lifetime tester software [1] which accounts for band-gap narrowing in the substrate agrees within 3 % over the full range of assumed base doping. Furthermore we show that the carrier-lifetime in the substrate shows a significant influence on J 0 -values obtained using the absolute measured recombination and leads to overestimation of up to 50 % even for high base-lifetimes of τ SRH = 1 ms. The implemented parameter-set and analysis method is based on common accepted models and consistent with various simulation tools, and thus allows for the extraction and comparison of injection- and substrate-independent J 0 -values.