Effect of Silicon Surface for Perovskite/Silicon. Tandem Solar Cells: Flat or Textured?

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1 Supporting Information Effect of Silicon Surface for Perovskite/Silicon Tandem Solar Cells: Flat or Textured? Hiroyuki Kanda, Naoyuki Shibayama, Abdullah Uzum, Tomokazu Umeyama, Hiroshi Imahori,, Koji Ibi, and Seigo Ito * Corresponding author: itou@eng.u-hyogo.ac.jp (Seigo Ito) Department of Materials and Synchrotron Radiation Engineering, Graduate School of Engineering, University of Hyogo, 2167 Shosha, Himeji, Hyogo, , Japan Department of Electrical and Electronics Engineering, Karadeniz Technical University, 61080, Trabzon, Turkey Department of Molecular Engineering, Graduate School of Engineering and Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University, Nishikyo-ku, Kyoto, , Japan Choshu Industry Co., Ltd., 3740 Shin-Yamanoi, Sanyo-Onoda, Yamaguchi, , Japan 1

2 The effect of the thin Au layer on optical properties was investigated by comparing the transmittance of glass/au layer and glass only (Figure S-1). Figure S-1. Optical transmittance of glass/au layer (2.5 nm) and glass only 2

3 In order to calculate the reflectance of samples, Fresnel equations were used as follows. The complex index of reflection η considering polarization and incident angle can be written as where the number of 0, j, and m represent air medium, number of each layer, and silicon substrate, as shown in Figure S-1. Figure S-2. Schematics image of an angle of incident light from air into each layer and the silicon substrate. 3

4 The S and P show polarization of spectra. The θ is an angle of incidence. The N and n means complex index of refraction of normal incident, which can be represented by where k means extinction coefficient. The N and θ can be shown by Snell s law as The complex index of reflection of incident medium can be written as where k 0 is written by since the extinction coefficient of the air medium is 0. 4

5 The complex index of reflection of each layer and the substrate can be written as where x and y represent as below With the equations (6) and (7), the Fresnel coefficient ρ of each layer can be written as 5

6 From equation (8), the Fresnel coefficient of layer of the number L, where polarization is omitted, can be shown as The relationship of the Fresnel coefficient of L and L-1 can be written as where λ and d represent wavelength and thickness of each layer, respectively. 6

7 From equations (9), (10) and (11), eventually, the reflectance R can be calculated as In our simulation, the reflectance was calculated as the average of s and p polarization. If the reflection of the textured surface was squared it is assumed to have approximately double the reflection of the pyramidal structure. 7

8 In order to show the thickness of the perovskite layer, cross sectional SEM images are shown in Figure S-2. The thickness of the perovskite layer was controlled by spin-coating speed explained in experimental section. The thickness of the perovskite layer was 400 nm (Figure S-2a) with 5000 rpm and 500 nm (Figure S-2b) with 4000 rpm, respectively. Figure S-3. Cross sectional SEM image of the perovskite solar cell with (a) thin (400 nm) and (b) thick (500 nm) perovskite layer. 8

9 To compare semitransparent perovskite top cell and reference perovskite solar cell structured <FTO/TiO 2 /CH 3 NH 3 PbI 3 /Spiro-OMeTAD/Au(60 nm)>, I-V properties of reference cell are shown in Figure S-4 and Table S-1. Figure S-4. I-V curves of reference solar cell structured <FTO/TiO 2 /CH 3 NH 3 PbI 3 / Spiro-OMeTAD/Au(60 nm)> and semitransparent solar cell with thin (400 nm) and thick (500 nm) perovskite layer. 9

10 Table S-1. Photovoltaic properties of reference solar cell structured <FTO/TiO 2 /CH 3 NH 3 PbI 3 /Spiro-OMeTAD/Au(60 nm)> and semitransparent solar cell with thin (400 nm) and thick (500 nm) perovskite layer. Thin perovskite layer (400 nm) Thick perovskite layer (500 nm) Cell type Scan direction J SC V OC FF Eff. J SC V OC FF Eff. (ma cm -2 ) (V) (-) (%) (ma cm -2 ) (V) (-) (%) Reference Forward solar cell Reverse Semitransparent Forward solar cell Reverse