Simultaneously improving optical absorption of both transverse-electric-polarized and
transverse-magnetic-polarized light for organic solar cells with Ag grating used as
transparent electrode
Yongbing Long,a Yuanxing Li, Runmei Su
School of Applied Physics and Material, WuYi University, Jiangmen, 529020, China
Supplemental materials
The supplementary materials include three parts：（1）Microcavity theory; (2)
Optical resonance effects of the weak-microcavity within Device B and C ;(3) Optical
resonance effects of the metal-mirror-microcavity within Device C
1. Microcavity theory
In grating-based Device B and C, a weak-microcavity (WMC) is constructed
with Glass/WO3 interface and Ag back electrode as mirrors and a metal-mirror
microcavity (MMC) is constructed with the Ag strips in grating and Ag back electrode
as mirrors, as is shown in Fig.1(a) in the manuscript. According to the cavity theory,
the cavity mode is determined by the thickness and optical constants of all the layers
in the devices and can be described by the following equation: 1, 2
n d
i
i
i

1

m
 2
4
4
2
(1)
Where ni and d i are respectively the refractive index and thicknesses of the layers
between cavity mirrors;  1 and  2 are the reflection phase shift of cavity mirrors;
 is the wavelength of the incident light; m is the mode number. The left term of the
equation denotes the total optical length of the microcavity, and is named as L() .
2. Optical resonance effects of the WMC within Device B and C
The resonance effects of the WMC structure are investigated by calculating the
ratio of the optical length of the WMC structure to the half-wavelength of the incident
light (i.e., ( 2L( ) /  )).The results are shown in Fig. S1, which demonstrates that
a
Corresponding author. E-mail address: yongbinglong@gmail.com;
2L( ) /  for Device B without the capping WO3 layer is not equal to any integer
number in the visible wavelength of 400-700nm. In other words, the WMC structure
within Device B does not resonate in this wavelength range. Despite this, 2L( ) / 
in the red wavelength range is close to zero and the WMC in Device B is near
zero-order resonance.
4-5
Consequently, relatively large optical electric field can be
confined within the device. This ultimately leads to absorption improvement within
the red wavelength range for Device B, as is shown in Fig. 2 (c). As to Device C with
both Ag grating and capping WO3 layer, 2L( ) /  equals to 1.0 at the wavelength of
488nm (m=1). Around this wavelength, the first-order optical resonance occurs,
improving the optical electric field within the active layer. Correspondingly,
absorption for Device C can be improved in a broad wavelength range when
compared with that for Device A.4,5
Figure.S1 2L( ) /  of the WMC structure within Device B and C.
3. Resonance mode of the MMC within Device C
To determine the resonance mode of the MMC structure within Device C, we
calculate the ratio of the optical length of the MMC structure to the half-wavelength
of the incident light (i.e., ( 2L( ) /  )) . The results are shown in Fig. S2, where
2L( ) /  equals to 0 at the wavelength of 445nm. This wavelength is the resonance
mode of the MMC structure within Device C. Around the resonance mode, large
optical electric field is confined within MMC structure and light absorption can be
improved.
Figure.S2 2L( ) /  of the MMC structure within Device C.
Reference：
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61, 943,2014