Issue
EPJ Photovolt.
Volume 12, 2021
EU PVSEC 2021: State of the Art and Developments in Photovoltaics
Article Number 6
Number of page(s) 6
DOI https://doi.org/10.1051/epjpv/2021007
Published online 09 November 2021

© M. Rienäcker et al., Published by EDP Sciences, 2021

Licence Creative CommonsThis is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

1 Introduction

The photovoltaic (PV) market demands for ever higher PV module efficiencies. Polysilicon-on-oxide (POLO) passivating contacts and interdigitated back-contact (IBC) cell technologies have recently attracted a lot of interest as candidates for the implementation in industrial production in the near future. However, the realization of an IBC cell with POLO junctions for both polarities − a POLO2-IBC cell − requires a separation of the highly defective p+ and n+ poly-Si regions on the rear side of the cell to avoid parasitic recombination. Beside the trench separation [1] and local oxidation of the poly-Si [2], inserting an initially undoped, intrinsic (i) region between the p+ and n+ poly-Si regions − as reported by several research groups [36] − was demonstrated to successfully prevent the parasitic recombination in the transition region [5,7]. In 2018, a POLO2-IBC cell with such a p+-(i)-n+ POLO interdigitated rear side achieved an efficiency of 26.1% [5], even without an optimized hydrogenation scheme for the POLO junctions. Thus, we recently applied hydrogen-donating layer stacks on symmetric POLO junction samples to demonstrate a significant improvement of the passivation quality compared to that implemented in the 26.1%-efficient cell from 2018 [8]. Moreover, we developed the required laser ablation process for the hydrogen-donating layer stack to be able to create laser contact openings without damaging the POLO junction underneath [9]. In this contribution, we study the interplay of hydrogen-donating layers with the p+-(i)-n+ POLO interdigitated rear side of our POLO2-IBC cell. Since the typical hydrogen-donating layers like Al2O3 or SiNy accommodate a high positive or negative charge, we investigate the influence of such a charge on the POLO2-IBC cell performance. We find that any strong charge density at the p+-(i)-n+ POLO interdigitated rear side leads to enhanced non-ideal recombination and diminishes the performance of POLO2-IBC solar cells.

2 Experimental

2.1 POLO2-IBC solar cell precursor with different rear side dielectric layers

Figure 1a shows the structure of the precursor stage of our POLO2-IBC solar cell fabricated similar to references [5,7]. One characteristic feature of this cell is the p+-(i)-n+ POLO interdigitated rear side, where the p+-type poly-Si and n+-type poly-Si regions are separated by an initially intrinsic (i) poly-Si region. The term “initially” refers to the fact that during high-temperature annealing, strong lateral diffusion of dopants in the poly-Si (on the length scale of several micrometres) yields an inter-diffused lateral junction [7].

In brief, the following fabrication process yielded the cell precursor in Figure 1a: A 2.2 nm-thin interfacial oxide layer was thermally grown onto a 1.3 Ωcm, p-type FZ wafer, which was subsequently capped by a low pressure chemical vapor deposited (LPCVD) intrinsic amorphous Si layer. We performed masked ion implantation of boron and phosphorous into the amorphous Si on the rear side and a blanket phosphorous implantation on the front side. For the former, the PECVD-deposited SiOx implant mask barriers were patterned by photolithography, such that a gap of 30 μm i poly-Si remained between the n+-type and p+-type poly-Si fingers. Then, the amorphous Si recrystalized during a pyrogenic oxidation at 900 °C to grow a ∼200-nm-thick SiO2 layer and the POLO junction formed in a subsequent higher temperature process at 1035 °C. This step also yielded a lateral interdiffusion of dopants on the length scale of several micrometers, resulting in an inter-diffused junction within the initially 30 μm wide intrinsic poly-Si region [7]. The inter-diffused junction still isolates the charge carrier in the n+ poly-Si from that in the p+ poly-Si region. Hartenstein et al. have recently confirmed experimentally that the compensation of dopants at the p+-(i)-n+ poly-Si junction provides a highly resistive narrow region, which separates n+ poly-Si and p+ poly-Si electrically [10].

As in references [5,7], the POLO junctions on the rear side were hydrogenated by depositing a sacrificial hydrogen-containing, silicon-rich SiNy layer on the thick thermal SiO2 layer and by subsequently annealing for 30 min at 425 °C. Eventually, the SiNy layer was removed in hot phosphoric acid.

Starting with a cell precursor as in Figure 1a, which has resulted in a cell efficiency of 26.1% in reference [3], an advanced hydrogenation scheme from Section 2.2 is applied to obtain the cell precursor in Figure 1b with improved POLO junctions on the rear side. For this purpose, we removed the SiO2 layer from the front side and texturized it. Then, we remove the SiO2 layer from the rear side and passivated the front side. On the rear side, we deposited a layer stack of a 20-nm-thick Al2O3, a 30-nm-thick hydrogen-containing silicon-rich SiNy and a 200-nm-thick PECVD-SiOz, which was subsequently annealed for 30 min at 425 °C.

Alternatively, we removed the layer stack from the rear side of the cell precursor in Figure 1b by a single-sided HF etching and replaced it by a 20-nm-thick PECVD-SiOz and a 30-nm-thick SiNy to obtain the cell precursor in Figure 1c. As indicated in Figure 1c, the 200-nm-thick SiOz is missing on the rear side of the sample for simplicity, but has to be included in the final cell for optical reasons. The minority carrier lifetime of each cell precursor is characterized by spatially resolved infra-red lifetime mapping (ILM) [11].

Furthermore, using the same front-end process of the cell precursors in Figure 1a and b, symmetrical reference wafers with full-area doped POLO junction are fabricated and characterized by using the Sinton lifetime tester.

thumbnail Fig. 1

(a–c) Schematic drawing of the structure of a POLO2-IBC solar cell with (a) a thermally grown SiO2 layer, (b) Al2O3/SiNy/SiOz or (c) PECVD-SiOz/SiNy stack as the rear side dielectric layer. (d–f) Spatially resolved carrier lifetime of the cell structures shown in (a–c) at ∼0.25 suns measured by the ILM method. The active cell areas of the seven solar cells are marked with squares a–g.

2.2 Advanced hydrogenation of POLO junctions

While the ∼200 nm-thick thermally grown SiO2 in Figure 1a was necessary in reference [5] to enable a damage-free local laser ablation to create contact openings, it hinders the hydrogenation of the POLO junctions from hydrogen-donating SiNy layer to some extent. We replaced the SiO2 by a layer stack of Al2O3/hydrogen-rich SiNy/Al2O3, which is known to be an efficient hydrogen-donating layer stack [12] to estimate the upper limited for the passivation quality of the POLO junctions used for the 26.1%-efficient POLO2-IBC cell. To study the effect of the improved hydrogenation scheme, symmetric p+ POLO, n+ POLO and iPOLO samples were prepared following the procedure in Section 2.1. After POLO junction formation, the thermally grown SiO2 was replaced by Al2O3/hydrogen-rich SiNy/Al2O3 and annealed at temperatures above 425 °C.

2.3 Charging of the p+-(i)-n+ rear side of the POLO2-IBC solar cell precursor

In order to investigate the influence of charged dielectric layers at the p+-(i)-n+ rear side on the cell performance, we systematically manipulated the charge density at the rear side of cell precursor in Figure 1a and monitored the recombination behavior of the cell precursor at each charging condition. For this purpose, we deposited corona charges on top of the thermally grown SiO2 by means of a needle-plate electrode corona discharge at 8 kV. A single charging step yielded a charge density of 4.5e11 cm−2. We measured the recombination behavior of the cell precursor by using infrared lifetime mapping [11] at different illumination intensities and calculated the illumination-dependent implied open-circuit voltage Suns-iVOC characteristic of the cell precursor at each charging state.

3 Results

Figure 1d shows the lifetime map of the cell wafer from Figure 1a, which contains seven cell regions (a–g) and four reference regions for iPOLO. The lifetime within the cell region b and e reach values of 1.8 ms due to the good passivation of the n+ POLO and p+ POLO junctions. In this stage, the full-area POLO references reveal a saturation current density of 4 fA/cm2 and 5.5 fA/cm2 for n+ POLO and p+ POLO junctions, respectively. However, as already reported in reference [7], the intrinsic reference region (iPOLO) in Figure 1d is almost unpassivated and therefore yields low lifetimes. In contrast to that, properly hydrogenated iPOLO junctions have been reported elsewhere [4]. This is a strong evidence that the thick SiO2 hinders hydrogen from reaching the thin interfacial SiOz of the iPOLO junctions of the 26.1%-efficient cell in reference [5] and that the hydrogenation of n+ and p+ POLO junctions is not optimal. Thus, it seems straight forward to apply a better hydrogenation scheme to improve the POLO2-IBC cell efficiency of 26.1% towards 27%.

Indeed, when replacing the thick SiO2 layer by the Al2O3/hydrogen-rich SiNy/Al2O3 layer stack and performing an annealing above 425 °C, we have been able to improve the saturation current density of our n+ POLO and p+ POLO junctions on symmetric lifetime samples down to below 0.5 ± 03 fA/cm2 and 3.3 ± 0.7 fA/cm2 [8], respectively. For the iPOLO junction sample, an effective surface recombination velocity Seff of approximately 12 cm/s is achieved after hydrogenation, which is more than an order of magnitude lower compared to the iPOLO junction of the 26.1%-efficient cell [7]. The improved hydrogenation of the n+ and p+ POLO junctions from 4 fA/cm2 and 10 fA/cm2 to 0.5 fA/cm2 and 3.3 fA/cm2 was estimated to result in an efficiency improvement of ∼0.4%abs. by means of device simulations [8].

To prove the benefit of an improved hydrogenation scheme on the cell level, we deposited a similar hydrogen-donating Al2O3/SiNy/SiOz layer stack as evaluated above on the cell precursor. This results in the structure shown in Figure 1b. Figure 1e depicts the lifetime map of the cell precursor. As expected from the hydrogenation experiments above, the iPOLO reference region of the wafer improves significantly upon hydrogenation and exhibits a lifetime of 1.5 ms. After hydrogenation, the full-area POLO references of the cell precursor in Figure 1b reveal a saturation current density of 2.5 fA/cm2 and 4 fA/cm2 for n+ POLO and p+ POLO junctions, respectively. Regardless of the improvement of the POLO junctions, the lifetime within cell regions drops from previously 1.5–1.8 ms for the cell precursor as shown in Figure 1a to about 200–300 μs for that in Figure 1b.

We explain this surprising observation by the high density of negative fixed charge in the Al2O3 layer in contrast to the almost neutral SiO2 layer. The negative charge density in the dielectric layer or at its interface to poly-Si causes an upward band bending within the poly-Si layer close to its interface with the dielectric layer [13]. Thus, we expect an accumulation of holes and a depletion of electrons in the first few nm of the poly-Si layer at the Al2O3 interface in the degenerately doped p+ and n+ poly-Si region, respectively.

In the initially undoped region between the p+ and n+ poly-Si regions, the compensation of dopants after high temperature annealing results in a moderately doped, graded pn junction. In the case of an almost absent surface charge on top of the poly-Si layer e.g., with a SiO2 layer, one part of this transition region exhibits a high resistivity and ensures electrical isolation between the p+ and n+ poly-Si regions. However, upon applying the Al2O3 layer, its strong negative fixed charge manipulates the carrier population in the moderately doped transition region, such that an accumulation and inversion layer form in the moderately doped p-type and n-type poly-Si regions, respectively. The carrier population modulation and the transport barrier lowering due to electrostatics significantly increase the carrier mobility within the poly-Si [1418]. Thus, the Al2O3 effectively establishes a hole-conductive channel at its interface to the poly-Si at the p+-(i)-n+ POLO interdigitated rear side [13]. This conductive channel connects the highly defective p+ and n+ poly-Si regions and results in a strong recombination of electrons with holes. A similar enhanced recombination was already observed for POLO2-IBC cells without an initially intrinsic poly-Si between p+ and n+ poly-Si regions [6,19,20].

In order to confirm our hypothesis, we corona charge the SiO2 surface of the cell precursor in Figure 1a and measure the implied open circuit voltage iVoc versus illumination intensity characteristic. We systematically manipulate the charge density on the rear side by depositing a corona charge density QC on top of the SiO2. First, we investigate the effect of negative charges and notice that the effect of charging the rear side on the lifetime of the precursor weakens over time. We speculate that this second order effect is due to the instability of corona charges on top of the SiO2 layer [21,22]. On the time scale of the experiment, this instability causes an uncertainty with respect to the actual amount of charges present on the SiO2. Qualitatively, the experiment still yields valid data. Moreover, we utilize this effect to return to the state of the cell precursor without corona charging. To reach this state, we deposit approximately the same amount of positive charges as negative charges previously applied and wait about 60 hours for the charge to neutralize. We start from this state of the precursor to study the effect of positive corona charges applied to the SiO2.

Figure 2 summarizes the Suns-iVOC characteristics for different QC values. If negative corona charges are deposited, the Suns-iVOC curve at implied voltages close to the maximum power point of the final 26.1% cell (640 mV [5,7]) shifts towards higher illumination intensities, which corresponds to an increased non-ideal recombination with a high local ideality factor (up to 3) and which diminishes the implied pseudo fill factor. Close to one-sun conditions, the effect of charging is minor and the local ideality factor is about 0.9 for the uncharged state and 1.2 with a corona charge density of −2.7e12 cm−2. For positive corona charges, the Suns-iVOC characteristic improves slightly up to a corona charge density of 0.9e12 cm−2. Further increasing the positive charge densities lead again to enhanced non-ideal recombination at around a voltage of 640 mV − similar to negative charges.

Figure 3 shows the implied pseudo-efficiency iη of the cell precursor, which results from the Suns-iVOC characteristic with an assumed constant short-circuit current density of 42.6 mA/cm2 as has been measured for the 26.1% efficient cell in references [5,7]. Without corona charging, the cell precursor has an iη of 26.4%, which drops suddenly for negative QC. If a corona charge density of 0.5e12 cm−2 or 0.9e12 cm−2 is applied, the iη increases to about 26.5%, but drops again sharply for larger QC.

Given the results in Figures 2 and 3, it can be understood why the cell precursor in Figure 1b with Al2O3 on the rear side with a typical charge density of −4e12 cm−2 and the cells in reference [6] exhibits a worse recombination behavior and a compromised cell performance − even if the POLO junction's passivation quality is improved upon hydrogenation. Moreover, we expect that a cell with a strongly positively charged SiNy hydrogen-donating layer would cause the same effect. Therefore, an IBC cell with a p+-(i)-n+ POLO interdigitated rear side requires an almost uncharged hydrogen-donating dielectric layer on the rear side − at least in the transition region of the p+-(i)-n+ junction.

Replacing the strongly charged Al2O3 layer by a weakly charged − optimally hydrogen-containing − PECVD/ALD-SiOz or SiOzNy on the rear side of the cell precursor in Figure 1b poses one possibility for such a dielectric layer stack, which could also be compatible with the laser contact opening process in reference [9].

To demonstrate that a PECVD-SiOz meets the requirement of being weakly charged and that it is suitable for the application on the rear side of POLO2-IBC cells, we removed the Al2O3/SiNy/SiOz dielectric layer stack from a cell precursor as shown in Figure 1b and subsequently deposited a non-optimized PECVD-SiOz and a SiNy on the rear side. The resulting cell structure is depicted in Figure 1c. The cell precursor with a PECVD-SiOz /SiNy layer stack on the rear side shows a strongly improved performance in Figure 1f compared to that with an Al2O3/SiNy/SiOz layer stack in Figure 1e. The cell precursors in Figure 1f exhibit an implied pseudo-efficiency of up to 26.3%. This is qualitatively comparable with the cell precursor from Figure 1d without corona charging. However, the front side passivation of the cell precursor in Figure 1a deviates from that in Figure 1c and the meaningfulness of a comparison of both cell precursors on an absolute efficiency scale is limited. However, the successful implementation of the PECVD-SiOz on the rear side of a POLO2-IBC cell precursor represents a good starting point for future optimization towards 27%-efficient POLO2-IBC cells.

thumbnail Fig. 2

Illumination-dependent implied open-circuit voltage Suns-iVOC characteristic of the cell precursor from Figure 1a as a function of the applied corona charge density QC at the thermally grown SiO2 on the rear side. The inset magnifies the Suns-iVOC around 1 sun conditions.

thumbnail Fig. 3

Implied pseudo-efficiency iη for a cell precursor as shown in Figure 1a as a function of the applied corona charge density QC. Blue data points were measure first and the red ones about 60 hours after the blue data set. The arrows indicate the fixed charge density of Al2O3 and SiNy on c-Si. Typical charge densities for SiOz are marked in gray.

4 Conclusion

In this contribution, we aimed at implementing hydrogen-donating layers on the p+-(i)-n+ POLO interdigitated rear side to improve our POLO2-IBC cell with an efficiency of 26.1% towards an efficiency of 27%. Since the typical hydrogen-donating layers like Al2O3 or SiNy accommodate a high positive or negative charge, we investigated the influence of such a charge on the POLO2-IBC cell performance. We fabricated POLO2-IBC cell precursor with three different dielectric layers/layer stacks on the rear side: (i) a thermally grown SiO2 as has been used for the 26.1% cell; (ii) a hydrogen-donating Al2O3/SiNy/SiOz stack to improve POLO junction passivation quality; (iii) a hydrogen-donating PECVD-SiOz/SiNy stack. The implied pseudo-efficiency iη of each precursor was deduced from the illumination-dependent implied open-circuit voltage Suns-iVOC of the cell precursor.

While the cell with thermally grown SiO2 showed the expected iη of 26.4%, a comparison with the second cell precursor indicated that the hydrogenation scheme with the thick SiO2 is less efficient compared to the Al2O3/SiNy/SiOz stack. The second cell precursor with Al2O3/SiNy/SiOz stack efficiently hydrogenated the POLO junction, but yielded a cell precursor with worse recombination behavior and low performance. We attributed this surprising observation to the presence of a strong negative charge induced by the Al2O3 layer.

To confirm this hypothesis, we studied the influence of charges at the p+-(i)-n+ POLO interdigitated rear side on the POLO2-IBC cell performance. We systematically manipulated the charge density by depositing a corona charge density on top of the SiO2 covering the rear side. We found that strong positive or negative charge densities cause an enhanced non-ideal recombination and degrade the cell performance significantly, which is most likely due to the formation of a conductive path for electrons or holes within the highly defective poly-Si. Fortunately, the thermally grown SiO2 has a nearly ideal charge density and its iη can only slightly be improved by 0.1%abs to 26.5% by adding a positive corona charge density of below 0.9e12 cm−2.

We conclude that it is vital to control the charge density of the dielectric layers applied to the p+-(i)-n+ POLO interdigitated rear side to avoid a strong increase of non-ideal recombination at the p+-(i)-n+ poly-Si junction. While this effect is highly pronounced for IBC cells with poly-Si, it may also apply − to some extend − to all types of IBC cells with charged dielectric layers on the interdigitated rear side.

Finally, we presented a weakly charged hydrogen-donating layer stack comprising a 20-nm-thin and a potentially weakly charged PECVD-SiOz at the interface with the poly-Si capped by a hydrogen-donating SiNy layer. This stack may provide an efficient hydrogenation scheme, while maintaining the isolation between p+ and n+ poly-Si regions. A first cell precursor with the weakly charged hydrogen-donating layer stack yielded an iη of 26.3%.

Author contribution statement

M. R., Y. L., S. W. and R. P. designed the investigations of the improved hydrogenation and discussed the results. Y. L. supervised the experiments with respect to the improved hydrogenation, acquired and analyzed the data. M. R., J. K. and R. P. supervised the processing of the solar cell precursors. M. R. designed the corona charging experiments, collected and analyzed the data, and wrote the original draft. R. P. and R. B. supported the POLO work at ISFH with many fruitful discussions, corrected the manuscript and acquired the financial support. All authors discussed the results and revised the manuscript.

Acknowledgments

The authors thank the state of lower Saxony and the Federal Ministry of Economic Affairs (BMWi) for funding this work, which was performed in the framework of the research project “27Plus6” (FKZ03EE1056A). We are grateful to Hilke Fischer, Sarah Spätlich and Renate Winter (all from ISFH) as well as Raymond Zieseniss and Guido Glowatzki (both from Institute of Electronic Materials and Devices) for sample processing. We thank Felix Haase and Christina Hollemann for fruitful discussions.

References

  1. D. De Ceuster, P.J. Cousins, D.D. Smith, Trench process and structure for backside contact solar cells with polysilicon doped regions, Patent US Patent 7,851,698, 2010 [Google Scholar]
  2. U.R. Robby Peibst, Solar cell and a method for producing a solar cell with oxidised intermediate regions between polysilicon contacts, Patent WO2016184840A2, 2015 [Google Scholar]
  3. J.C.M. Choi, H. Park, Solar cell and method for manufacturing the same, Patent EP 2797124A1, 2013 [Google Scholar]
  4. D.L. Young, W. Nemeth, V. LaSalvia, R. Reedy, S. Essig, N. Bateman, P. Stradins, Interdigitated back passivated contact (IBPC) solar cells formed by ion implantation, IEEE J. Photovolt. 6, 41 (2016) [Google Scholar]
  5. F. Haase, C. Hollemann, S. Schäfer, A. Merkle, M. Rienäcker, J. Krügener, R. Brendel, R. Peibst, Laser contact openings for local poly-Si-metal contacts enabling 26.1%-efficient POLO-IBC solar cells, Solar Energy Mater. Solar Cells 186, 184 (2018) [Google Scholar]
  6. C. Reichel, R. Müller, F. Feldmann, A. Richter, M. Hermle, S.W. Glunz, Influence of the transition region between p- and n-type polycrystalline silicon passivating contacts on the performance of interdigitated back contact silicon solar cells, J. Appl. Phys. 122, 184502 (2017) [Google Scholar]
  7. C. Hollemann, F. Haase, M. Rienäcker, V. Barnscheidt, J. Krügener, N. Folchert, R. Brendel, S. Richter, S. Großer, E. Sauter, J. Hübner, M. Oestreich, R. Peibst, Separating the two polarities of the POLO contacts of an 26.1%-efficient IBC solar cell, Sci. Rep. 10, 658 (2020) [Google Scholar]
  8. R. Peibst, M. Rienäcker, Y. Larionova, N. Folchert, F. Haase, C. Hollemann, S. Wolter, J. Krügener, P. Bayerl, J. Bayer, M. Dzinnik, R. Haug, R. Brendel, Towards 28%-efficient Si single junction solar cells with better passivating POLO junctions, Sol. Energy Mat. Sol. Cells (submitted) [Google Scholar]
  9. M. Rienäcker, Three-terminal tandem solar cellsenabled by back-contacted bottom cellsfeaturing passivating, carrier-selectivepolysilicon based junctions, Ph.D. dissertation, submitted to Gottfried Wilhelm Leibniz Universität Hannover, 2021 [Google Scholar]
  10. M.B. Hartenstein, S. Harvey, M. Page, D. Young, P. Stradins, S. Agarwal, Effect of dopant compensation on the conductivity of the intrinsic poly-Si isolation region in passivated ibc silicon solar cells, in 2020 47th IEEE Photovoltaic Specialists Conference (PVSC). IEEE (2020) pp. 2751–2753 [Google Scholar]
  11. K. Ramspeck, S. Reissenweber, J. Schmidt, K. Bothe, R. Brendel, Dynamic carrier lifetime imaging of silicon wafers using an infrared-camera-based approach, Appl. Phys. Lett. 93, 102104 (2008) [Google Scholar]
  12. M.K. Stodolny, J. Anker, C.J.J. Tool, M. Koppes, A.A. Mewe, P. Manshanden, M. Lenes, I.G. Romijn, Novel schemes of p+ poly-Si hydrogenation implemented in industrial 6 bifacial front-and-rear passivating contacts solar cells, in 35th European Photovoltaic Solar Energy Conference and Exhibition (2018), pp. 414–417 [Google Scholar]
  13. A. Grove, D. Fitzgerald, Surface effects on pn junctions: Characteristics of surface space-charge regions under non-equilibrium conditions, Solid-State Electr. 9, 783 (1966) [Google Scholar]
  14. J.Y.W. Seto, The electrical properties of polycrystalline silicon films, J. Appl. Phys. 46, 5247 (1975) [Google Scholar]
  15. B. Tyagi, K. Sen, On the resistivity of polycrystalline silicon, Phys. Stat. Solidi 80, 679 (1983) [Google Scholar]
  16. C.H. Seager, Grain boundaries in polycrystalline silicon, Annu. Rev. Mater. Sci. 15, 271 (1985) [Google Scholar]
  17. H.N. Chern, C.L. Lee, T.F. Lei, An analytical model for the above-threshold characteristics of polysilicon thin-film transistors, IEEE Trans. Electr. Dev. 42, 1240 (1995) [Google Scholar]
  18. M.K.H. Mark Stewart, High performance gated lateral polysilicon PIN diodes, Solid-State Electr. 44, 1613 (2000) [Google Scholar]
  19. U. Römer, R. Peibst, T. Ohrdes, B. Lim, J. Krügener, T. Wietler, R. Brendel, Ion implantation for poly-Si passivated back-junction back-contacted solar cells, IEEE J. Photovolt 5, 507 (2015) [Google Scholar]
  20. M. Rienäcker, A. Merkle, U. Römer, H. Kohlenberg, J. Krügener, R. Brendel, R. Peibst, Recombination behavior of photolithography-free back junction back contact solar cells with carrier-selective polysilicon on oxide junctions for both polarities, Energy Proc. 92, 412 (2016) [Google Scholar]
  21. W. Olthuis, P. Bergveld, On the charge storage and decay mechanism in silicon dioxide electrets, IEEE Trans. Electr. Insulat. 27, 691 (1992) [Google Scholar]
  22. R.S. Bonilla, C. Reichel, M. Hermle, P. Hamer, P.R. Wilshaw, Long term stability of c-si surface passivation using corona charged SiO2 , Appl. Surf. Sci. 412, 657 (2017) [Google Scholar]

Cite this article as: Michael Rienäcker, Yevgeniya Larionova, Jan Krügener, Sascha Wolter, Rolf Brendel, Robby Peibst, Rear side dielectrics on interdigitating p+-(i)-n+ back-contact solar cells − hydrogenation vs. charge effects, EPJ Photovoltaics 12, 6 (2021)

All Figures

thumbnail Fig. 1

(a–c) Schematic drawing of the structure of a POLO2-IBC solar cell with (a) a thermally grown SiO2 layer, (b) Al2O3/SiNy/SiOz or (c) PECVD-SiOz/SiNy stack as the rear side dielectric layer. (d–f) Spatially resolved carrier lifetime of the cell structures shown in (a–c) at ∼0.25 suns measured by the ILM method. The active cell areas of the seven solar cells are marked with squares a–g.

In the text
thumbnail Fig. 2

Illumination-dependent implied open-circuit voltage Suns-iVOC characteristic of the cell precursor from Figure 1a as a function of the applied corona charge density QC at the thermally grown SiO2 on the rear side. The inset magnifies the Suns-iVOC around 1 sun conditions.

In the text
thumbnail Fig. 3

Implied pseudo-efficiency iη for a cell precursor as shown in Figure 1a as a function of the applied corona charge density QC. Blue data points were measure first and the red ones about 60 hours after the blue data set. The arrows indicate the fixed charge density of Al2O3 and SiNy on c-Si. Typical charge densities for SiOz are marked in gray.

In the text

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.