Manufacturable Nanostructured Solar Cells with Efficient Light Trapping and Charge Carrier Collection Investigators

Photovoltaics, which utilizes the largest possible energy source to generate electricity, represents one of the most attractive approaches towards renewable energy future. However, the cost of current solar electricity is still too high. Future photovoltaic technologies need to have high power conversion efficiency and can be fabricated with low cost. In this project, we propose novel nanocone and nanodome-like solar cells, which can reduce the cost while enhancing the power efficiency. We design by photonics simulation and fabricate subwavelength inorganic nanostructured substrate, on which solar cell layers can be deposited. We will study our light trapping device concept on solar absorber materials. Our device concept for light trapping is general and is expected to reduce the amount of materials needed, to increase manufacturing throughput and to reduce the capital cost which will be able to reduce the solar cell production cost significantly while still maintaining high efficiency. Our proposed research can lead to important fundamental understanding of photon management in photovoltaics and to the fundamental design of high efficiency solar cells. Background Converting sunlight energy into an easily usable format is one of the most attractive solutions toward renewable energy future since everyday sun delivers energy to the earth 10,000 times of the current world energy consumption. Photovoltaic devices, which convert sunlight energy into electricity, are therefore widely studied as a means to harvest solar energy. Although the solar cell industry has indeed seen a large growth rate in the last couple of decades, the energy produced by solar cells only contributes to less than 0.1% of the world total energy consumption. One of the main reasons is that solar electricity is still significantly more expensive than traditional electricity generated by fossil fuels. Solar cell operation includes a number of physical processes to be optimized. When sunlight reaches the solar cell, some of the light is reflected back and lost, so that a special antireflection layer is needed to minimize the loss. This requires either a material with low refractive index or a textured morphology. Furthermore, to maximize the light absorption the active semiconductor layer needs to be thick enough to harvest as many photons as possible. For crystalline silicon, an indirect bandgap semiconductor, the typical film thicknesses is three hundred micrometers. Last but not least, the electrons and holes created by the absorbed photons need to be separated and collected to generate electricity with minimum loss. Maximizing the light absorption requires a thick layer of absorber although increasing charge carrier collection efficiency and decreasing the cost favors the opposite: thin absorber layer. It is necessary to develop a solar cell structure with efficient antireflection and light trapping simultaneously so that only a thin layer of absorber layer is needed for photon absorption. It is also important to develop facile processing to produce such solar cell structures. In this project, we study nanocone and nanodome solar cells for efficient photon management. We will study our light trapping device concept on materials including CdTe and CuIn1‐xGax Se2 (CIGS).