Effectively transparent front contacts for optoelectronic devices achieve a measured transparency of up to 99.9% and a measured sheet resistance of 4.8 Ω sq^(−1). The 3D microscale triangular cross-section grid fingers redirect incoming photons efficiently to the active semiconductor area and can replace standard grid fingers as well as transparent conductive oxide layers in optoelectronic devices

Atwater, Harry A.

Borsuk, Aleca M.

Bukowsky, Colton R.

Emmer, Hal S.

Lloyd, John V.

Saive, Rebecca

Yalamanchili, Sisir

Caltech Authors - Main

Copyright WILEY-VCH Verlag GmbH & Co. KGaA, 69469 Weinheim, Germany, 2016.
Supporting Information
for Adv. Optical Mater., DOI: 10.1002/adom.201600252
Effectively Transparent Front Contacts for Optoelectronic
Devices
Rebecca Saive, Aleca M. Borsuk, Hal S. Emmer, Colton R.
Bukowsky, John V. Lloyd, Sisir Yalamanchili, and Harry A.
Atwater*
Supplemental: Effectively transparent front contacts for 
optoelectronic devices 
Rebecca Saive1, Aleca M. Borsuk1, Hal S. Emmer1, Colton R. Bukowsky1, John V. Lloyd1, Sisir Yalamanchili1,                     
and Harry A. Atwater1* 
1 Department of Applied Physics and Material Science, California Institute of Technology, Pasadena, CA 91125, USA 
S1: Optical simulations and measurements of the wavelength and angle dependence 
Figure S1.1: a) Measured wavelength dependent reflection and b) angle dependent reflection of areas on the solar cell with flat lines, triangular 
cross-section lines and only the antireflection coating. Angle and wavelength dependent reflection measurements were performed in a 
spectrophotometer equipped with an integrating sphere. The spectrophotometer instrument uses chopped monochromated light from a 
supercontinuum laser and a silicon photodiode detector, as described elsewhere (M.D. Kelzenberg, PhD thesis, 2010). The axis of angular 
rotation was aligned parallel to the contact finger lines or triangular contacts (compare angle α in Fig. S1.2). In contrast to the spatially resolved 
photocurrent measurements presented in the main manuscript in Fig. 2 the illumination spot size used in these measurements is large (~ 200 
µm), and averages over regions with good fidelity in the fabricated triangular cross-section contact structure, along with regions containing 
imperfections. 
 
  
Figure S1.2: Ray optical (Lighttools) simulation of the wavelength and angle dependence of the transmission through a grid of free-standing a), c) flat 
silver lines and b), d) triangular cross-section silver lines. In a) and b) the angle was varied perpendicular to the line (angle α on the right side), in c) and 
d) the angle was varied parallel to the contact lines (angle β on the right side). Decreased transparency in the short wavelength regime can be attributed 
to losses in the silver. 
 
 S2 Optical simulation of triangular cross-section line patterns with different periods 
 
 
Figure S2: Simulation of the transparency of 
free-standing, solid silver triangular cross-
section lines depending on the wavelength and 
on the period of the line pattern. The simulation 
was performed by two-dimensional rigorous 
coupled wave analysis (RCWA) using RSofts’s 
DiffractMOD in order to account for wave 
optical effects occurring particularly for smaller 
periods. Periods between 3 µm and 20 µm and 
wavelengths between 280 nm and 1107 nm 
were simulated. The triangular lines were 2.5 
µm wide and 7.0 µm high. Thus, e.g. a period 
of 6.0 µm corresponds to a gap of 3.5 µm. It 
can be seen that the transparency remains 
almost 100 % for periods down to around 5 
µm. Decreased transparency in the short 
wavelength regime can be attributed to losses 
in the silver. 
 
 
 
 
 
 S3: Comparison of different photonic approaches to improved front contact transparency 
Title  Authors Paper Scheme Transparency Equivalent 
current* 
Sheet 
resistance 
Effectively 
transparent 
front contacts 
for 
optoelectronic 
devices 
Rebecca Saive, 
Aleca M. Borsuk, 
Hal S. Emmer, 
Colton R. 
Bukowsky, John 
V. Lloyd, Sisir 
Yalamanchili, and 
Harry A. Atwater 
This  
paper 
 
99.9 % 41.21 
mA/cm2 
 
4.8 Ω/sq 
24.7% Record 
Efficiency HIT 
Solar Cell on 
Thin Silicon 
Wafer 
Mikio Taguchi, 
Ayumu Yano, 
Satoshi Tohoda, 
Kenta 
Matsuyama, Yuya 
Nakamura, 
Takeshi 
Nishiwaki, 
Kazunori Fujita, 
and Eiji 
Maruyama 
IEEE 
Journal of 
Photovolt
aics 4, 96-
99 (2014) 
 
~ 96.6 %1 
 
(only grid 
fingers, 
deduced from 
geometry and 
current) 
39.5 
mA/cm2 
~ 5 Ω/sq1 
Hybrid Metal–
Semiconductor 
Nanostructure 
for Ultrahigh 
Optical 
Absorption and 
Low Electrical 
Resistance at 
Optoelectronic 
Interfaces 
Vijay K. 
Narasimhan, 
Thomas M. 
Hymel, Ruby A. 
Lai, and Yi Cui 
ACS nano 
9, 10590-
10597 
(2015) 
 97 % 
absorption, 
with 4.2 % 
parasitic 
absorption 
within metal  
 92.8 % 
transmission 
38.40  
mA/cm2 
Below 20 
Ω/sq 
Cloaked 
contact grids 
on solar cells 
by coordinate 
transformation
s: designs and 
prototypes 
Martin F. 
Schumann, 
Samuel 
Wiesendanger, 
Jan Christoph 
Goldschmidt, 
Benedikt Bläsi, 
Karsten Bittkau, 
Ulrich W. 
Paetzold, 
Alexander 
Sprafke, Ralf B. 
Wehrspohn, 
Carsten 
Rockstuhl, and 
Martin Wegener 
Optica 2, 
850-853 
(2015) 
 
Transparency 
not explicitly 
reported. 
--- Not 
reported 
but this 
geometry 
should 
allow for 
low sheet 
resistance. 
Catoptric 
electrodes: 
transparent 
metal 
electrodes 
using shaped 
surfaces 
Pieter G. Kik Optics 
letters 39, 
5114-
5117 
(2014) 
 
84 % 
(Simulation) 
34.68 
mA/cm2 
Not 
reported 
but this 
geometry 
should 
allow for 
low sheet 
resistance. 
Transparent 
metallic fractal 
electrodes for 
semiconductor 
devices 
Farzaneh 
Afshinmanesh, 
Alberto G. Curto, 
Kaveh M. 
Milaninia, Niek F. 
van Hulst, and 
Mark L. 
Brongersma 
Nano 
letters 14, 
5068-
5074 
(2014) 
 
No average 
transparency 
reported.  
--- No sheet 
resistance 
reported. 
Performance 
enhancement 
of metal 
nanowire 
transparent 
conducting 
electrodes by 
mesoscale 
metal wires 
Po-Chun Hsu, 
Shuang Wang, 
Hui Wu, Vijay K. 
Narasimhan, 
Desheng Kong 
Hye Ryoung Lee 
and Yi Cui 
Nature 
communic
ations 4 
(2013) 
 
92 % 38.10 
mA/cm2 
0.36 Ω/sq 
Transparent 
Conducting 
Silver 
Nanowire 
Networks 
Jorik van de 
Groep, Pierpaolo 
Spinelli, and 
Albert Polman 
Nano 
Letters 
12, 3138-
3144 
(2012) 
 
91 % 37.67 
mA/cm2 
6.5 Ω/sq 
 
* The equivalent circuit is calculated at the example of the 24.7 % efficiency Panasonic HIT cell (IEEE Journal of Photovoltaics 4, 96-99 
(2014)). The grid fingers are replaced by using a contact structure with the reported transparency, the busbars are kept the same. 
Furthermore, a current of 1.21 mA/cm2 is subtracted in order to account for parasitic absorption within the amorphous silicon. 
For our contact structure we also performed a realistic ray tracing simulation that takes the front texture of silicon in real solar cells and 
losses in the amorphous silicon into account. Note, that it is not clear for all structures reported here how integration with structured 
silicon would be achieved.  
1 These values are not explicitly given in the paper but deduced from the optical and electrical properties by comparison with similar 
solar cells. 
 
 
 
 
 
 
 
 
 
 
 
 
 
S4:  Additional spatially resolved laser beam induced photocurrent measurement 
The left figure shows a spatially resolved laser beam induced photocurrent measurement of an area on the very same solar cell used for 
the measurement in Fig 2. In this area an approximately 100 nm silver layer covers the flat lines as a result from the angular 
evaporation. The silver was evaporated from the right side so that right of the line there is a silver hill while left of the line is only little or 
no silver. From the profile shown on the right side, it can be seen that there is a non-negligible photocurrent induced between the lines 
although this area was covered with around 100 nm of silver. The signal goes down to zero at the position of the silver hills showing that 
this is not a measurement artifact but that 100 nm of silver transmit a significant amount of light.  
 
  
 
 
 
 
S5:  Electrical properties of the line grid 
 
 


Effectively Transparent Front Contacts for Optoelectronic Devices

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Effectively Transparent Front Contacts for Optoelectronic Devices

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