Аctive layers nanosructuring in solar cells based on amorphous hydrogenated silicon

Head of the laboratory: Prof. V.P. Afanasiev

Relevance of the project

Nanoscaling of a-Si:H imparts the following fundamental properties to the material:

  • large value of light absorption coefficient for straight-band electronic transition at k = 0;
  • carriers diffusion length of about 100 nm in the i-part and less in doped sublayers.

Development of the new technological ways for multilayer nanosystems preparation which include nanoheterostructural cascade photovoltaic cells based on a-Si:H and other hydrogenated semiconductors, signified a new milestone in the field of renewable energy. In case of amorphous materials it opened the door to formation of low-cost solar cells. Nowadays the efficiency of the modules based on amorphous silicon is 6.8%, while in the laboratory conditions use of complex cascade heterostructures enables efficiency of 15%. One of the promising ways to improve efficiency of solar cells is to combine amorphous silicon with microcrystalline silicon that results in tandem (cascade) solar cells with efficiency of 8% for industrially implemented samples. There are also prerequisites for further increase in efficiency up to 9-10% based on optimization of solar cells, use of new materials, design modifications and methods of multilayer structure formation.

The project is aimed at solution of the following problems

  1. Improving the quality of a-Si:H material. Effective management of excitation current and injected carriers at the stages of generation and transport in order to control recombination processes, in particular, the reduction of losses in the active region of the solar cell.
  2. Development of effective deposition technology, which results in stable and radiation-resistant a-Si:H films formed on the surface of transparent conductive oxide, to increase the service life of a-Si:H layers and solar cell as a whole.
  3. Ensuring cascade coupling, namely search for optimal parameters of a-Si:H layers deposition technology (thickness, doping, mixed solutions, etc.), including the use of various modifications and sublayer defect structure.
  4. Development of effective contact formation technology based on preparation of textured layers of transparent conductive oxide (TCO, ITO, etc.) in order to increase the percentage of radiation absorbed by solar cell layers at the interface, optimize surface morphology, electrical, physical and chemical properties of contact layers.
  5. Investigation of two-phase media:
    • a-Si:H – nc-Si (nanocrystalline silicon);
    • a-Si:H – nM (metal nanoclusters of Ag, Au, Cu, Al, etc.);
    • ncp-Si (porous nanocrystalline silicon) – nM.

Expected results of the project

  1. Increase in efficiency of solar cells based on the developed a-Si:H deposition technology from 8 to 10%.
  2. Reduction of solar cell parameters degradation through the use of a thin "generating" layer in the i-layer. This layer can be formed by application of the RF power increased by 3-4 times as compared to that used at the stage of i-layer deposition.
  3. The use of textured layers will increase short-circuit current by 25% due to light reflection from these layers and optimization of total internal reflection. The top electrodes will be made of conductive oxides such as SnO2:F, In2O3-SnO2 (ITO), ZnO:Al which are characterized with high transparency (> 90%), large band gap (> 3.5 eV) and low surface resistivity (<10 Ohm/cm2).
  4. Technological equipment for production of converters based on amorphous silicon allows formation of single-module elements of large area - over 1-3 m2, which is about 100 times greater than the size of the module based on crystalline silicon. This fact reduces the cost of solar photovoltaic plant construction significantly.