Comprehensive experimental and numerical optimization of surface morphology of transparent conductive oxide films for tandem thin film photovoltaic cells

Abstract

Typical thin-film photovoltaic cells incorporate a textured transparent conductive oxide to efficiently harvest solar energy. What should be the ideally desired morphology of this textured surface for best cell performance -is highly debated but remains an unsolved mystery. We present a comprehensive methodology to 1) accurately model, 2) extract macroscopically sufficient statistical finger-prints and 3) predict best desired values for these statistical finger-prints of such a randomly textured surface for the best performance of the cell.

Rigorous optical simulation of light management in crystalline silicon thin film solar cells with rough interface textures

“…M. Agrawal et al 5 suggest that the height and angular distributions of a rough surface contain sufficient information for the description of light trapping by rough surfaces. In contrast to the ACF method employed in this paper the surface construction algorithm is not yet imposed in their approach.…”

“…Near field investigations have been done by Bittkau et al 2 and Rockstuhl et al 3,4 In their work intensity distributions measured by near field scanning optical microscopy were compared to rigorous 3D simulations. A study employing rigorous simulation to obtain wavelength resolved generation rates was released by M. Agrawal et al 5 Aside from these and a few other contributions to solar cell simulation a lot of work has been put into rigorous rough surface scattering simulations for bistatic radar applications. [6][7][8] The physical properties of these systems are somewhat different than for solar cells.…”

Rigorous optical modeling and optimization of thin‐film photovoltaic cells with textured transparent conductive oxides

“…A typical schematic and transmission electron micrograph (TEM) of the cross section of a double‐junction tandem amorphous silicon (a‐Si) and microcrystalline silicon (µc‐Si) solar cell is shown in Figure . Most of the high efficiency thin‐film silicon solar cells in superstrate configuration are grown on glass substrates coated with a randomly textured transparent conductive oxide (TCO) film . One of the major bottlenecks in achieving the full efficiency potential of silicon‐based tandem‐junction (TJ) thin‐film photovoltaic (PV) technology is the understanding and optimization of textured TCO films as front contacts .…”

“…Most of the high efficiency thin‐film silicon solar cells in superstrate configuration are grown on glass substrates coated with a randomly textured transparent conductive oxide (TCO) film . One of the major bottlenecks in achieving the full efficiency potential of silicon‐based tandem‐junction (TJ) thin‐film photovoltaic (PV) technology is the understanding and optimization of textured TCO films as front contacts . The design and understanding of textured TCO film become very complex as it serves three different roles with often conflicting requirements—the film needs to have very low sheet resistance, the film needs to provide a good optical impedance match between the ambient and the rest of the cell, which means it should absorb or reflect as little optical power as possible over the broad visible spectrum, and the film needs to optimally scatter light to increase effective path lengths in silicon, particularly in the long wavelength range .…”

“…One of the major bottlenecks in achieving the full efficiency potential of silicon‐based tandem‐junction (TJ) thin‐film photovoltaic (PV) technology is the understanding and optimization of textured TCO films as front contacts . The design and understanding of textured TCO film become very complex as it serves three different roles with often conflicting requirements—the film needs to have very low sheet resistance, the film needs to provide a good optical impedance match between the ambient and the rest of the cell, which means it should absorb or reflect as little optical power as possible over the broad visible spectrum, and the film needs to optimally scatter light to increase effective path lengths in silicon, particularly in the long wavelength range . Moreover, as the length scales of textures and the thicknesses of various layers in the PV cell stack are smaller than or similar to the wavelengths of interest, the optical interference effects cannot be ignored .…”