Nano-Photonic Structures for Light Trapping in Ultra-Thin Crystalline Silicon Solar Cells.
Thick wafer-silicon is the dominant solar cell technology. It is of great interest to develop ultra-thin solar cells that can reduce materials usage, but still achieve acceptable performance and high solar absorption. Accordingly, we developed a highly absorbing ultra-thin crystalline Si based solar cell architecture using periodically patterned front and rear dielectric nanocone arrays which provide enhanced light trapping. The rear nanocones are embedded in a silver back reflector. In contrast to previous approaches, we utilize dielectric photonic crystals with a completely flat silicon absorber layer, providing expected high electronic quality and low carrier recombination. This architecture creates a dense mesh of wave-guided modes at near-infrared wavelengths in the absorber layer, generating enhanced absorption. For thin silicon (<2 μm) and 750 nm pitch arrays, scattering matrix simulations predict enhancements exceeding 90%. Absorption approaches the Lambertian limit at small thicknesses (<10 μm) and is slightly lower (by ~5%) at wafer-scale thicknesses. Parasitic losses are ~25% for ultra-thin (2 μm) silicon and just 1%-2% for thicker (>100 μm) cells. There is potential for 20 μm thick cells to provide 30 mA/cm² photo-current and >20% efficiency. This architecture has great promise for ultra-thin silicon solar panels with reduced material utilization and enhanced light-trapping.
Ames Laboratory, Microelectronics Research Center, Iowa State University, Ames, IA 50011, USA. prathap@nplindia.org.|Silicon Solar Cell Division, CSIR-National Physical Laboratory, Dr. K.S. Krishnan Road, New Delhi-110012, India. prathap@nplindia.org.
Prathap
P
Pathi
Ames Laboratory, Microelectronics Research Center, Department of Electrical and Computer Engineering, Iowa State University, Ames, IA 50011, USA. apeer@iastate.edu.
Akshit
A
Peer
Ames Laboratory, Microelectronics Research Center, Department of Physics and Astronomy, Department of Electrical and Computer Engineering, Iowa State University, Ames, IA 50011, USA. biswasr@iastate.edu.
Rana
R
Biswas
light-trapping; nano-photonics; scattering; solar cell