Compound semiconductors and silicon solar cells for industrial applications

POF III / Topic 1 Solar cells of next generation

Subtopic 2 - Compound Semiconductors

Thin-film photovoltaic (PV) modules are a promising alternative to crystalline silicon-based devices when it comes to Terawatt-scale deployment of photovoltaic modules. In particular chalcopyrite Cu(In,Ga)(Se,S)2 (CIGS) based solar cells offer conversion efficiencies exceeding 22% and can compete with crystalline silicon solar cells. Additionally, thin-film deposition techniques allow the use of flexible substrates such as polymer or metal foils and convenient integration into building components like facades or roof tiles. However, there are several challenges when it comes to thin-film compound materials:

  • Transfer of high efficiency of small laboratory devices to large area modules
  • Reduction of manufacturing cost by developing fast, low-cost deposition with minimized material usage
  • Avoiding toxic and rare elements

The CIGS-Teams at PVcomB follow two main routes for the formation of CIGS, which are both technologically relevant: A three-stage coevaporation [PVD-CIGS] process that yields high-efficiency devices on small substrates (5 x 5cm2) and a 30 x 30 cm² research line following the sequential processing route [RTP-CIGS] by firstly depositing metal precursor layers followed by an atmospheric pressure rapid-thermal processing (AP-RTP) in elemental selenium (Se)- or sulfur (S)-vapor to form Cu(In,Ga)(Se,S)2 absorber layers.

POF III / Topic 1 Solar cells of next generation

Subtopic 3 - Silicon solar cells

Subtopic 3 “Silicon Solar Cells” addresses the next generation of a PV technology that has proven its suitability for mass production but needs a substantial research effort to fit into a future PV scenario with respect to cost and efficiency. The topic aims at efficient and versatile silicon based solar cell devices overcoming present efficiency restrictions. To  this end, new material and new design options are combined with a continuous improvement of state-of-the-art technologies. In addition, the versatility of the technology is used  to develop specific solutions for integrating photovoltaic components into chemical or electrochemical storage systems.

Silicon-based multi-junction devices (task 3.1, task 3.3)

Fig. 1: Layer stack of an a-Si:H/µc-Si:H tandem solar cell.

Besides tandem cells this technology offers the possibility to design a variety of single, tandem, triple and even “quadruple” [5] junction devices with various and adjustable current-to-voltage ratios. In combination with other materials and devices, this allows for hybride devices. Two applications have been successfully demonstrated with solar cell devices from PVcomB:

  • The combination of an a-Si:H single junction with an organic upconverter [6].
  • The combination of an a-Si:H/a-Si:H tandem junction with an organic solar cell reaching a conversion efficiency of >11 % [7].
  • The integration of an a-Si:H/a-Si:H/µc-Si:H triple junction in a device for photocatalytic hydrogen splitting device [8]. Here, in particular the high output voltage (Vmpp) > 1.4 V, needed for water splitting, is an advantage.

The objectives in this task are:

  • Maintaining an in-house TF-Si baseline as a state-of-the-art reference line for thin film Si PV modules, in order to monitor equipment and processes and to support the other tasks.
  • Support of the existing industry partners as well as offering a technology basis for future industrial applications in hybrid applications (task 3.3).
  • Development of a technology basis to provide tailor-made devices for task 3.3. The key challenge in order to develop these novel multi-junctions is to tailor the silicon device and process in order to fulfill the specific requirements, such as: specific voltage/current combinations, e.g. a restricted process temperature window, an adapted contacting scheme , a specific choice of substrate, or design of interfaces and surfaces e.g. for chemical resistivity to certain electrolytes.

[1]   S Kirner, O Gabriel, B Stannowski, B Rech, R Schlatmann, The growth of microcrystalline silicon oxide thin films studied by in situ plasma diagnostics, Applied Physics Letters 102 (5), 051906-051906-4.

[2]   F. Ruske, M. Roczen, K. Lee, M. Wimmer, S. Gall, J. Hüpkes, D. Hrunski, B. Rech, Improved electrical transport in Al-doped zinc oxide by thermal treatment, J. Appl. Phys. 107, 013708 (2010).

[3]   S. Neubert, M. Wimmer, F. Ruske, S. Calnan, O. Gabriel, B. Stannowski, R. Schlatmann, B. Rech, Improved conversion efficiency of a-Si:H/µc-Si:H thin-film solar cells by using annealed Al-doped zinc oxide as front electrode material, Prog. Photovolt: Res. Appl. (2013).

[4]   B. Stannowski, O. Gabriel, S. Calnan, T. Frijnts, A. Heidelberg, S. Neubert, S. Kirner, S. Ring, M. Zelt, B. Rau, J.-H. Zollondz, H. Bloess, R. Schlatmann, B. Rech, Achievements and challenges in thin film silicon module production, Solar Energy Materials and Solar Cells 119 (2013) 196–203.

[5]   S. Kirner, S. Neubert, C. Schultz, O. Gabriel, B. Stannowski, B. Rech, and R. Schlatmann Quadruple-junction solar cells and modules based on amorphous and microcrystalline silicon with high stable efficiencies, Japanese Journal of Applied Physics 54, 08KB03 (2015).

[6]   Y.Y. Cheng et al., Improving the light-harvesting of amorphous silicon solar cells with photochemical upconversion, Energy Environ. Sci. 5, 6953 (2012).

[7]   S. Roland et al., Hybrid Organic/Inorganic Thin‐Film Multijunction Solar Cells Exceeding 11% Power Conversion Efficiency, Advanced Materials 27 (7), 1262-1267.

[8]   P. Bogdanoff, D. Stellmach, O. Gabriel, B. Stannowski, R. Schlatmann, R. v.d. Krol, S. Fiechter, Artificial Leaf for Water Splitting Based on a Triple‐Junction Thin‐Film Silicon Solar Cell and a PEDOT:PSS/Catalyst Blend, Energy Technology 4 (1), 230-241 (2016).

Silicon Heterojunction (SHJ) solar cells (Task 3.2)


A way for the silicon wafer technology to face future challenges in efficiency increase and cost reduction is by developing high efficient silicon heterojunction (SHJ) solar cells. Therefore, a SHJ Baseline process for industrial cells up to 6-inch size has been established at PVcomB. At PVcomB, research is focused on using process know-how from the a-Si:H/µc-Si:H technology to SHJ cell technology by implementing advanced silicon and silicon alloy materials and processes, such as nc-SiOx:H, from the AKT tool.

Currently SHJ cell efficiencies of 22.5 %, certified by ISFH CalTeC, are obtained. The research is strongly supported and embedded in industrial collaborations and receives significant external funding from national and European sources. Cell efficiencies of 24.5 % for double-side and 25 % efficient all-rear side contacted (IBC) SHJs are target until 2018 (PV 1.3.7)



Solar cells and modules based on liquid-phase crystallized silicon on glass (LPCSG) (Task 3.4)

For solar cells based on liquid-phase crystallized silicon (LPC-Si), as developed in task 3.4, an excellent passivation of the contacts is needed in order to benefit from the high quality of the LPC-Si absorber. This is addressed in close cooperation with the SHJ work in task 3.2, with the deposition of low-resistive and passivated contacts carried out in the AKT tool.