Two dimensional (2D) periodic photonic nanostructures, fabricated by nanoimprint lithography (NIL) and dry etching on
the front surface of crystalline silicon (c-Si) layers, are investigated experimentally and theoretically in order to
characterize their optical properties and demonstrate their relevance to photovoltaic (PV) applications. Nanoimprint
lithography is performed on c-Si wafers and ultra-thin c-Si films with various thicknesses. A comparison with state-ofthe-
art front side texturing with an antireflection coating is made. The 2D periodic photonic nanostructures result in an
enhanced light absorption in the photoactive material. The results are validated through simulations based on Rigorous
Coupled Wave Analysis (RCWA). The nanoimprinted substrates result in a similar absorption compared to the state-ofthe-
art random pyramid texturing while consuming less than a micron of photoactive material. In contrast to the random
pyramid texturing, the nanopatterning exhibits a robust performance for a wide range of incident angles up to 70°. The
light trapping mechanism we propose is based on the combination of a graded index effect and the diffraction of light
inside the photoactive layer at high angles.
In this paper, we present the integration of an absorbing photonic crystal within a monocrystalline silicon thin film solar
cell stack. Optical simulations performed on a complete solar cell revealed that patterning the epitaxial monocrystalline
silicon active layer as a 1D and 2D photonic crystal enabled to increase its integrated absorption by 38%rel and 50%rel in
the whole 300-1100 nm range, compared to a similar but unpatterned stack. In order to fabricate such promising cells, a
specific fabrication process based on holographic lithography, inductively coupled plasma etching and reactive ion
etching has been developed and implemented to obtain such photonic crystal patterned solar cells. Optical measurements
performed on the patterned stacks highlight the significant absorption enhancement, as expected by simulation. A more
advanced structuration combining a front and a rear 1D binary photonic patterning with different periods is designed,
enabling a 60%abs larger absorption in silicon.
In this paper, we present the integration of an absorbing photonic crystal within a thin film photovoltaic solar cell.
Optical simulations performed on a complete solar cell revealed that patterning the epitaxial crystalline silicon
active layer as a 1D and 2D photonic crystal enabled to increase its integrated absorption by 37%abs and 68%absbetween 300 nm and 1100 nm, compared to a similar but unpatterned stack. In order to fabricate such promising
cells, a specific fabrication processes based on holographic lithography, inductively coupled plasma etching and
reactive ion etching has been developed and implemented to obtain ultrathin patterned solar cells.
We present the integration of an absorbing planar photonic crystal within a thin film photovoltaic cell. The devices are
based on a stack including a hydrogenated amorphous silicon P-i-N junction surrounded by TCO layers, with a back
metallic contact. Optical simulations exhibit a significant increase of the integrated absorption in the 300-720nm
wavelength range. The global electro-optical characteristics of such a new solar cell, and the impact of surface
passivation, are also discussed. Carrier generation rate maps calculated by optical simulations are introduced as input
data in a commercial electrical simulation software. The fabrication of such a device is finally addressed, with a specific
focus on the use of low cost nanopatterning processes compatible with large areas.
The absorption of thin hydrogenated amorphous silicon layers can be efficiently enhanced through a controlled periodic
patterning. Light is trapped through coupling with photonic Bloch modes of the periodic structures, which act as an
absorbing planar photonic crystal. We theoretically demonstrate this absorption enhancement through one or two
dimensional patterning, and show the experimental feasibility through large area holographic patterning. Numerical
simulations show over 50% absorption enhancement over the part of the solar spectrum comprised between 380 and
750nm. It is experimentally confirmed by optical measurements performed on planar photonic crystals fabricated by
laser holography and reactive ion etching.
A design is proposed to significantly increase the absorption of a thin layer of absorbing material such as amorphous
silicon. This is achieved by patterning a one-dimensional photonic crystal (1DPC) in this layer. Indeed, by coupling the
incident light into slow Bloch modes of the 1DPC, we can control the photon lifetime and then, enhance the absorption
integrated over the whole solar spectrum. Optimal parameters of the 1DPC maximize the integrated absorption in the
wavelength range of interest, up to 45% in both S and P polarization states instead of 33% for the unpatterned, 100 nm
thick amorphous silicon layer. Moreover, the absorption is tolerant with respect to fabrication errors, and remains
relatively stable if the angle of incidence is changed.
We report on enhancement of thin layer absorption through photonic band-engineering of a photonic crystal
structure. We realized amorphous silicon (aSi) photonic crystals, where slow light modes improve absorption
efficiency. We show through simulation that an increase of the absorption by a factor of 1.5 is expected for a
model film of 100nm of aSi. The proposal is then validated by an experimental demonstration, showing a 50%
increase of the absorption of a demonstrator layer of 1μm thick aSi over a spectral range of 0.32 0.76μm.
This shows new possibilities of increasing the efficiency of thin film photovoltaic cells. Photonic crystal based
architecture are proposed and discussed.