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This work successfully demonstrates fast firing processes with a technical throughput of 13204 cells/h for M2- sized solar cells (assumption of a double-lane furnace and 25 mm distance between wafers). This throughput is significantly higher than the currently predicted throughput of approx. 8000 cells/h for thermal processes in the PV industry by the latest ITRPV report. The demonstrated throughput is achieved by increasing the furnace's belt velocity to 20 m/min without enlarging the furnace. Compared to the standard firing process of the authors' institution (at 6 m/min, yielding 3961 cells/h), the abovementioned faster process is approx. three times shorter but maintains a similar power conversion efficiency and contact adhesion quality, making the module compatibility promising. According to the "SCost" cost of ownership model, increasing the throughput from 8000 to 13204 cells/h reduces the firing process costs by approx. 37% (from 0.052 €Ct/Wp to 0.033 €Ct/Wp). Since no larger furnace is required, it is simple to implement the faster firing process in an industrial production line. [ABSTRACT FROM AUTHOR]

We have developed a fast firing oven (FFO) firing profile that mitigates light and elevated temperature induced degradation (LeTID) in boron doped passivated emitter and rear cells (PERC), made from high-performance multicrystalline silicon (hp mc) and mono-cast material. During LeTID testing, the highest degradation in relative efficiency in the samples fired with this profile is only -2%rel < Δη <-1%rel depending on the cell, compared to -5%rel < Δη < -6%rel in samples fired with the standard profile. To show that the benefit of this technique can be transferred to modules, the influence of the temperature profile during lamination was investigated. The effect of LeTID mitigation persisted after the simulated lamination process. This new firing profile did not significantly influence the initial efficiencies of the cells that have been fired with it compared to samples fired with a standard firing profile (-0.2%abs < Δη < +0.1%abs). Since the new FFO profile is only a slight alteration to a standard profile, it can be easily integrated into existing production lines. The altered firing profile therefore seems to be a promising way to handle the LeTID challenge and ensure highest cell efficiencies throughout the whole lifecycle of modules made from mono-cast, hp mc, and probably other types of silicon solar cells in the field. The mono-cast wafers used in this work were grown with the seed manipulation for artificially controlled defects technique (SMART). It solves the challenge of grain boundaries growing inward from the crucible wall by introducing dislocation clusters near the wall that prevent this growth. We show that the efficiency of cells that were made with this technique (21.4%) is similar to that of magnetically grown Czochralski (mCz) cells (21.6%) which were otherwise produced identically. A third group of hp mc cells which have also been identically produced except for an acidic texture instead of random pyramids, however only achieved 19.5% efficiency. Therefore, using a standard PERC process, SMART mono material is clearly superior to hp mc material and is similar to mCz silicon. We also show that mCz cells do not show LeTID degradation. [ABSTRACT FROM AUTHOR]

We present an approach for the determination of the locally averaged recombination parameter j0,met assigned to the metal contacts of a solar cell. A set of samples with test fields combined with an interpolation scheme allows the precise prediction of expected local photoluminescence imaging (PLi) intensities for virtually non-metallized sample areas with a standard deviation of 0.7%. The ratio of the actually measured PLi signal in a metallized test field with respect to the predicted signal of the virtually non-metallized test field then serves as an input for numerical simulations for the extraction of j0,met. We find a clear correlation of the locally determined j0,met with both, the local peak firing temperature measured in-situ by a thermal imaging system installed in the firing furnace and the local sheet resistance of the diffused n+-region. These results demonstrate the high capability and accuracy of our approach for the uniformity characterization of metallization-induced recombination losses [ABSTRACT FROM AUTHOR]

In this work, an inline IR thermography system as an innovative application for real-time contactless temperature measurement of wafers - both metallized and non-metallized - during the firing process has been successfully realized in an industrial firing furnace as proof-of-concept and example for a thermography system in a conveyor furnace. As observed by the new system, thermocouples seem to measure lower temperature on wafers - especially in combination with thermocouple-frames – than wafers exhibit at standard firing conditions (here up to ΔT ≈ 40 K). Further, highly resolved spatial temperature distribution could be successfully measured on the wafer. [ABSTRACT FROM AUTHOR]

The authors present their work on Aluminum fire through (Al-FT) contacts on the rear side of p-type bifacial PERC devices. On test structures, only exhibiting a rear screen-printed Al electrode, the authors demonstrate that widening the temperature profile in the peak firing zone has a beneficial impact on the implied Voc leading to an increase from 646 to 652 mV. The Photoluminescence based analysis is accompanied by scanning electron microscope analysis at finger cross-sections showing randomly distributed inverted-pyramid-shaped Al-Si contacts exhibiting a 0.5 to 2.5 µm thick back surface field. On cell level, the approach is not yet mature and a peak efficiency of 20.5 % could be achieved, which is in clear distance to the 21.3 % of the reference cell featuring additional laser openings and an Al non-fire through (Al-NFT) rear electrode. The Al-FT’s BSF seems not to exhibit the same quality compared to its NFT pendant, because Voc decreases by 8 mV at a similar effective BSF coverage. The need for narrow Al fingers and, simultaneously, a high specific resistance of the Al-FT paste of ≈ 40µΩcm, leads to a limited FF reaching 80.5 % compared to 81.3 % for the Al-NFT. [ABSTRACT FROM AUTHOR]