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)

Optical Absorption Enhancement in Solar Cells via 3d Photonic Crystal Structures

“…Secondly, it may excite the guided modes in the substrate [10]. Thirdly, it diffracts light into higher orders to permit for an elongation of the optical path in the absorption layer [9]. Finally, it may produce longitudinal slow-groupvelocity effects and the parallel interface refraction associated with transverse slow modes [15].…”

“…Wave optics approaches can be aimed at enhancing absorption for a certain range of wavelengths, which can be more advantageous for efficiency [3,4]. Several light trapping approaches of wave optics were studied such as plasmonics based designs [5], grating couplers [6], fluorescent concentrator systems [7], and photonic crystals (PhCs) [8][9][10]. A variety of means to refract, diffract, and reflect light are with the aim of increasing the absorption path length of light in the materials.…”

Spectrally-Selective Photonic Structures for PV Applications

“…To meet the third demand, the inverted opal can be fabricated from a conductive material. One of these materials is aluminium doped ZnO [58], but other materials like SiC are also possible. For such a system, a relative increase of 10% was predicted.…”

Light Trapping in Silicon Based Tandem Solar Cell: A Brief Review

“…Interestingly, the analysis 2) shows that the intensity of this confined light inside a non-absorbing textured film can be larger than the incident light intensity, implying that light absorption in such a film morphology can be enhanced. Since then a large number of investigations have been made on various types of solar cells, like single junction 5,6) , tandem [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] and triple junction solar cells [23][24][25][26] and considered as a state of the art technique to improve device performance.…”