Track A Basic Science

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138319/1/jia218438.pd

Dispersive elements for spectrum splitting in solar cell applications

Photovoltaic tandem and triple solar cells are currently being developed and produced with reasonable efficiencies at high technological cost. The concept of spectrum splitting has been proposed with the advantage of compatibility to all types of cells. Although additional optical efforts are to be made, external photon management can be achieved to match different solar cell combinations no matter which band gaps involved or how the cells are connected. We present an experimental study comparing optical devices based on either interference or diffraction for tandem and triple cell configurations. Whereas diffractive media such as gratings suffer intrinsically from higher order diffraction losses, devices based on interference such as Bragg filter can yield a significant efficiency increase. For a triple cell configuration consisting of GalnP/GalnAs/GaSb, a net efficiency gain of more than 30 % is shown in a solar cell simulator compared to the best cell in direct light

Micromorph silicon tandem solar cells with fully integrated 3D photonic crystal intermediate reflectors

A 3D photonic intermediate reflector for textured micromorph silicon tandem solar cells has been investigated. In thin-film silicon tandem solar cells consisting of amorphous and microcrystalline silicon with two junctions of a-Si/c-Si, efficiency enhancements can be achieved by increasing the current density in the a-Si top cell providing an optimized current matching at high current densities. For an ideal photon-management between top and bottom cell, a spectrally-selective intermediate reflective layer (IRL) is necessary. We present the first fully-integrated 3D photonic thin-film IRL device incorporated on a planar substrate. Using a ZnO inverted opal structure the external quantum efficiency of the top cell in the spectral region of interest could be enhanced. As an outlook we present the design and the preparation of a 3D self organized photonic crystal structure in a textured micromorph tandem solar cell

Three-Dimensional Photonic Crystal Intermediate Reflectors for Enhanced Light-Trapping in Tandem Solar Cells

A three-dimensional photonic crystal intermediate reflector for enhanced light trapping in tandem solar cells is presented. The intermediate reflector consists of a transparent and conductive ZnO:Al inverted opal sandwiched in between the top amorphous silicon and bottom microcrystalline silicon cell

3D photonic crystals for photon management in solar cells

Light management in single and tandem solar cells is becoming increasingly important to optimize the optical and electro-optical properties of solar cells. After a short introduction to state-of-the-art light management approaches, different applications of photonic crystals for photon management in solar cells are reviewed and discussed concerning their applicability. Results on direction- and energy-selective filters for ultra-lighttrapping, intermediate reflectors for optimal current matching in tandem cells, and photonic crystal coating for fluorescence collectors will be presented and discussed

3D photonic crystal intermediate reflector for micromorph thin-film tandem solar cell

Abstract The concept of 3D photonic intermediate reflectors for micromorph silicon tandem solar cells has been investigated. In thin-film silicon tandem solar cells consisting of amorphous and microcrystalline silicon with two junctions of a-Si/μc-Si, efficiency enhancements can be achieved by increasing the current density in the a-Si top cell. It is one goal to provide an optimized current matching at high current densities. For an ideal photon-management between top and bottom cell, a spectrally selective intermediate reflective layer (IRL) is necessary, which is less dependent of the angle of incidence than state-of-the-art thickness dependent massive interlayers. The design, preparation and characterization of a 3D photonic thin-film filter device for this purpose has been pursued straight forward in simulation and experimental realization. The inverted opal is capable of providing a suitable optical band stop with high reflectance and the necessary long wavelength transmittance as well and provides further options for improved light trapping. We have determined numerically the relative efficiency enhancement of an a-Si/μc-Si tandem solar cell using a conductive 3D-photonic crystal. We have further fabricated such structures by ZnO-replication of polymeric opals using chemical vapour deposition and atomic layer deposition techniques and present the results of their characterization. Thin film photonic IRL have been prepared at the rear side of a-Si solar cells. Completed with a back contact, this is the first step to integrate this novel technology into an a-Si/μc-Si tandem solar cell process. The spectral response of the cell is presented and compared with reference cells. (© 2008 WILEY-VCH Verlag GmbH \& Co. KGaA, Weinheim

3D photonic crystal intermediate reflector for micromorph thin-film tandem solar cell

Abstract The concept of 3D photonic intermediate reflectors for micromorph silicon tandem solar cells has been investigated. In thin-film silicon tandem solar cells consisting of amorphous and microcrystalline silicon with two junctions of a-Si/μc-Si, efficiency enhancements can be achieved by increasing the current density in the a-Si top cell. It is one goal to provide an optimized current matching at high current densities. For an ideal photon-management between top and bottom cell, a spectrally selective intermediate reflective layer (IRL) is necessary, which is less dependent of the angle of incidence than state-of-the-art thickness dependent massive interlayers. The design, preparation and characterization of a 3D photonic thin-film filter device for this purpose has been pursued straight forward in simulation and experimental realization. The inverted opal is capable of providing a suitable optical band stop with high reflectance and the necessary long wavelength transmittance as well and provides further options for improved light trapping. We have determined numerically the relative efficiency enhancement of an a-Si/μc-Si tandem solar cell using a conductive 3D-photonic crystal. We have further fabricated such structures by ZnO-replication of polymeric opals using chemical vapour deposition and atomic layer deposition techniques and present the results of their characterization. Thin film photonic IRL have been prepared at the rear side of a-Si solar cells. Completed with a back contact, this is the first step to integrate this novel technology into an a-Si/μc-Si tandem solar cell process. The spectral response of the cell is presented and compared with reference cells. (© 2008 WILEY-VCH Verlag GmbH \& Co. KGaA, Weinheim