Influence of back contact roughness on light trapping and plasmonic losses of randomly textured amorphous silicon thin film solar cells

Abstract

The influence of nanotextured metallic back contacts on light trapping and plasmonic losses of amorphous silicon solar cells was investigated. The optical losses of the back contact are determined by the texture of the metallic back contact and the dielectric constant of the interlayer between the solar cell and the metal back contact. The investigations show that the optical losses are highest if nano features are present at the back contact, while the texture of the front contact which propagates through the layer stack exhibits only a minor effect on the optical losses. V C 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4793415]Light trapping or photon management in thin film solar cells allows for both a reduction of the reflection losses and a gain in the optical path length of the incident light inside the absorber layer. 1,2 Light trapping can be maximized if the front and the back contacts are textured. The rough back contact scatters and diffracts longer wavelengths light, 3,4 but also enhances the optical absorption within the metaldielectric interface. [5][6][7][8][9] Plasmonic absorption in the back contact can be reduced by introducing a textured dielectric layer with a refractive index lower than that of amorphous silicon. Aluminum doped zinc oxide (ZnO) is very often used as an interlayer between the metal back contact and the silicon p-i-n diode. 10,11 Surface textures with lateral dimensions approaching the effective wavelength of the incident light in the dielectric interlayer can couple incoming light to plasmon modes. 13 Schematic sketches of thin film solar cells with and without ZnO interlayer are shown in Figs. 1(e)-1(h). For interlayers prepared by sputtering, the surface texture is determined by the roughness and the morphology of the nlayer of the p-i-n diode. Thin (100 nm) and thick (400 nm) interlayers exhibit almost identical roughness. The back contact roughness can be controlled by wet chemical etching of the zinc oxide interlayer in hydrochloric acid. The influence of ZnO interlayer surface morphology on the quantum efficiency and the short circuit current of the solar cell was investigated in this study.The amorphous p-i-n solar cells were prepared by plasma enhanced chemical vapor deposition (PECVD) on 1.43 m 2 glass substrates. Due to the high defect density and low carrier diffusion lengths of amorphous silicon, 12 the solar cell is very thin with total thickness of 320 nm. The glass substrates were coated with a randomly textured tin oxide (SnO 2 ) layer. Further details on the optical and electrical properties of the amorphous silicon layers are given in Ref. 12. The zinc oxide interlayers and silver (Ag) back) back contacts were prepared by DC magnetron sputtering. The zinc oxide interlayers exhibit a thickness of 400 nm. Cross sections of solar cells with and without zinc oxide interlayer are shown in Figs. 1(e)-1(h). The ZnO interlayer was then subjected to wet chemical etching in a 3% hydrochloric acid (HCl) solution for various etching times. The etchin...

Comparison of Light Trapping in Silicon Nanowire and Surface Textured Thin-Film Solar Cells

“…Decreasing the diameter of the nanowire down to 1-2 nm leads to the formation of quantum wires [2]. Quantum wells, quantum wires or quantum dots allow for the control of the band gap by tuning the size of the quantum structure [35,36]. In the case of silicon, the bulk band gap of 1.14 eV can be increased to 1.7 eV or larger.…”

“…A very small drop of both parameters will be observed. However, the situation is different for the solar cell with textured contact layers [27][28][29][30][31][32][33][34][35]. The formation of surface plasmon polaritons and localized plasmon polaritons can lead to a distinct drop of the quantum efficiency for long wavelengths.…”

“…The optical losses increase with increasing roughness of the back contact and decreasing thickness of the solar cell [30][31][32][33]. The optical losses are most sensitive to metal textures with dimensions ranging from 30 to 100 nm [33,35]. The optical losses can be reduced, but not prevented by inserting a dielectric layer with a low refractive index between the metal back reflector and the silicon solar cell [3,4,6,27,35].…”

“…The optical losses are most sensitive to metal textures with dimensions ranging from 30 to 100 nm [33,35]. The optical losses can be reduced, but not prevented by inserting a dielectric layer with a low refractive index between the metal back reflector and the silicon solar cell [3,4,6,27,35]. In the current study, and in most studies in the literature, a sputtered metal oxide film, e.g., zinc oxide, is inserted between the metal back reflector and the silicon solar cell.…”

Effect of back reflectors on photon absorption in thin-film amorphous silicon solar cells

“…As a rule, the nanotextured surface is utilized to satisfy such prerequisites for making productive solar cells (Kim et al 2011;Palanchoke et al 2012;Jovanov et al 2013a;Wang et al 2017). Moreover, it is conceivable to accomplish higher charge transporter era in the optically thin absorber if reflectivity in the back contact is enhanced (Palanchoke et al 2013;Chen et al 2016). The aluminum-doped zinc oxide (ZnO:Al) coordinated with metal has earned a ton of consideration regarding expanding the impression of light from the back contact and unabsorbed reflected light once more into the solar cell which additionally builds the light trapping Catchpole and Polman 2008;Jovanov et al 2017).…”