Surface Texturing to Fabricate Black Silicon for High-efficiency Solar Cells and LEDs

Forms Antireflective Layers on the Surface of Silicon Wafers that Improve Conversion Efficiency of Photovoltaics and Light Extraction of LEDs

This surface texturing develops subwavelength antireflective nanostructures on the faces of single-crystalline and multicrystalline silicon wafers to produce black silicon suitable for highly efficient photovoltaics and semiconductor light emitting diodes (LEDs). With the growing desire for renewable energy sources, the global photovoltaics market is projected to exceed $345 billion by 2020. Crystalline silicon wafers are fundamental components of the solar cells used for photovoltaic energy harvesting. Since the high surface reflectivity of silicon wafers inhibits energy absorption by limiting the spectrum of usable light, crystalline silicon solar cells must apply antireflection coatings to ensure efficient energy production. Alternatively, black silicon wafers achieve superior anti-reflection by modifying the surface of crystalline silicon with nanoscale structures that enable effective energy absorption from the broadest range of visible and infrared light. However, available procedures for producing black silicon involve complex lithographic processes that limit the speed of production and increase overall costs.

Researchers at the University of Florida have developed a simple surface texturing procedure that forms a broadband antireflection coating directly on the surface of crystalline silicon wafers. The black silicon formation is non-lithographic and uses a scalable, self-masking etching process that involves only a single step to enhance mechanical and environmental stability.

Application

Black silicon nanostructured crystalline wafers with high-antireflective performance that reduce all light within the spectrum from visible to infrared, improving the efficiency of photovoltaic conversion and light extraction for use in solar cells, semiconductor LEDs, or ultrasensitive biosensors

Advantages

• Creates black silicon wafers using a self-masking etching process that requires no lithographic steps, simplifying the process to support low-cost, large-scale fabrication
• Texturizes antireflective nanostructured surfaces that are effective in reducing light reflection over a broader spectrum of visible and infrared wavelengths, increasing the conversion efficiency of crystalline silicon solar cells and the light extraction efficiency of semiconductor LEDs
• Modifies for different substrates such as silicon (Si), gallium arsenide (GaAs), gallium antimonide (GaSb), indium phosphide (InP), and gallium nitride (GaN), enabling broadband antireflective surface layer formation for a variety of technological applications
• Etches using a single step with clear boundaries, resulting in targeted antireflective layers that have long lifetimes and high thermal and radiation stability

Technology

This nanoscale surface texturing of silicon wafers and other similar substrates establishes antireflective layers effective over a wide range of visible and infrared light. During a simple reactive ion etching (RIE) process, a polyimide substrate in contact with the wafer triggers a random distribution of micro-masks throughout the wafer, which results in the formation of random nanoscale pillars on the surface area not covered by the polyimide. Consequently, the surface of the wafer uncovered during this etching process demonstrates broadband antireflection performance superior to those formed by other surface texturing procedures.