The baseline for industrial production of high-efficiency silicon heterojunction solar cells

Fig. 1 Cross-sectional structure of a silicon heterojunction solar cell
Fig. 2 Process steps to develop SHJ solar cells

Silicon heterojunction solar cells, or SHJ solar cells for short, are solar cells that contain very thin amorphous silicon layers in addition to crystalline silicon layers (Fig. 1). These amorphous layers provide excellent passivation of the surfaces and thus enable high efficiencies. In addition, these solar cells have an advantageous temperature coefficient of rel. > -0.3 %/K and thus exhibit much better temperature behavior than conventional crystalline silicon solar cells. However, SHJ solar cells are not only convincing due to their performance, but also due to the low manufacturing effort. Only four process steps are required to manufacture SHJ solar cells (Fig. 2.). This means that production is much leaner than, for example, with the currently predominant PERC solar cells.

The Institute for Energy and Climate Research 5 - Photovoltaics - at Forschungszentrum Jülich (IEK-5) operates a baseline that covers the entire process technology for the industrial production of high-efficiency SHJ solar cells on M2 wafer size: from wet chemical pretreatment to thin film deposition and metallization. In addition, various measurement facilities are available for characterizing the finished solar cells and the respective layers.

Fig. 3 Wet-bench for texturing and cleaning of crystalline Si wafers
Fig. 4 Clean room environment for SHJ solar cell preparation

In the first process step, work is carried out on a wet bench from Arias (Fig. 3). The wet bench has five process basins and two rinsing basins in which different work steps such as saw damage removal, texturing, ozone cleaning, oxidation, removal of the oxide and rinsing by means of Quick Dump Rinse can be carried out. The basins can each accommodate a holder with 25 M2 wafers. Since the work or transport between the process steps is particle critical, it takes place in an Ionstatex clean room of class 5 or better (Fig. 4).

Subsequently, the various silicon layers are deposited on the wafers. Intrinsic and doped amorphous and nanocrystalline silicon layers as well as silicon oxide layers are deposited by plasma-enhanced chemical vapor deposition (PECVD) with the AK1000 from Meyer Burger (called MARIA at our institute) (Fig. 5). The system has three process chambers and two loading chambers, each of which can coat 9 M2-sized wafers. The processes are controlled in-situ by optical emission spectroscopy (OES). A throughput of 60 M2 cells per day is possible. However, other wafer sizes can also be coated.

Fig. 5 AK1000 PECVD system from Meyer Burger for deposition of silicon thin-films
Fig. 6 Sputtering system VISS 600 from Von Ardenne Anlagentechnik for deposition of TCO layers

In the third process step, transparent conductive oxide (TCO) layers are deposited. In the reference process, layers of indium tin oxide (ITO) are deposited on the solar cells with the VISS 600 from Von Ardenne Anlagentechnik (Fig. 6). However, silver layers or other TCOs such as aluminum-doped zinc oxide (ZnO:Al) and indium tungsten oxide (IWO) can also be deposited with the equipment we call LISSy.

In the final process step, the metal contacts are applied to the solar cells by screen printing. The Micro-tec MT-650TVC screen printer and various screens with different numbers and widths of fingers are available (Fig. 7). Busbars can be printed subsequently on the already printed fingers (dual print). Multiple prints to reduce finger resistance are also possible thanks to precise positioning. Since the amorphous silicon layers must not be processed at high temperatures, the silver paste used is special paste for SHJ solar cells, which hardens in the oven already at 200 °C.

Fig. 7 Micro-tec MT-650TVC screen printer used for metallization of SHJ solar cells
Fig. 8 LOANA measurement system from pv-tools for characterization of SHJ solar cells performance

For subsequent characterization of the SHJ solar cells, the LOANA measurement facility from pv-tools with the Sinus-220 light source from Wavelabs is available (Fig. 8). Here, for example, current-voltage (IV) and external quantum efficiency (EQE) measurements are possible. For even more comprehensive analytics, a number of other measurement techniques is also available, e.g. electro-, photoluminescence, QSSPC or ellipsometry.

What do we offer?

  • High efficiency SHJ solar cells
  • SHJ solar cells adapted for application in silicon tandem solar cells
  • Passivating contact layers for other silicon solar cells
  • Support for the development of SHJ solar cells
  • Support for partners in ramping up their SHJ solar cell production
  • Reference process line for the development of new processes, materials and metrology for suppliers to the SHJ solar cell industry
  • Further development of promising materials and processes from basic research for SHJ solar cells
  • Adapted solar cells for new advanced solar module concepts

Dr. Andreas Lambertz

Leiter Silizium Heterostruktur Solarzellen Baseline

  • Institute of Energy and Climate Research (IEK)
  • Photovoltaics (IEK-5)
Building 02.6 /
Room 3017
+49 2461/61-2885

Last Modified: 21.06.2024