Light management in planar silicon heterojunction solar cells via nanocrystalline silicon oxide films and nano‐imprint textures

Abstract

In order to increase the efficiency of high performance silicon heterojunction solar cells even further, it is paramount to increase the photoelectric current by enhancing the amount of light being captured within the absorber. Therefore, to reduce the parasitic absorption in the other layers, optoelectronically favorable hydrogenated nanocrystalline silicon oxide films can substitute the commonly used hydrogenated amorphous silicon layers. In this work, we systematically investigate the combination of hydrogenated nanocrystalline silicon oxide and front side nano‐imprint textures as anti‐reflection layers in silicon heterojunction solar cells. Ultimately, we were able to tune the parasitic absorption via variation of the front surface field layer and enhance the short‐circuit current of the planar solar cells by about 2 mA cm−2 due to a random silicon pyramid textured imprint layer. A maximum active area efficiency of 20.4% was achieved with a short‐circuit current of 37.7 mA cm−2.

Versatility of doped nanocrystalline silicon oxide for applications in silicon thin-film and heterojunction solar cells

“…2) as a rear-emitter layer. An active area efficiency act of 21.4 % for the best cell was achieved on a Si random pyramid textured 170 µm CZ Si wafer with an active area of approximately 3.4 cm² without any further optical or electrical optimization of the individual layers or their thicknesses as compared to nontextured solar cells [21].…”

“…1 a)). The main focus in this application is to reduce the parasitic absorption at the front of the solar cell due to the high transparency of nc-SiO x :H layers in comparison to a-Si:H [8,15,21]. At the same time, the conductivity of the employed layers has to be sufficient to maintain a high fill factor (FF) in the device.…”

“…Due to intrinsic design limitations of the microchannel plates and effects like deionization of ions only a limited fraction of the evaporated atoms can be collected, resulting in detection efficiencies around 60 % [29,30]. Even though the investigated films were deposited at slightly different deposition conditions [21] Fig. 3.…”

“…At the same time, the conductivity of the employed layers has to be sufficient to maintain a high fill factor (FF) in the device. Furthermore, nc-SiO x :H can be used at the rear of SHJ solar cells to serve as a rear-emitter layer [21] or a back surface field [23] ("II" in Fig. 1 a)).…”

“…Lastly, the cells were thermally annealed in air for 2 h at 220 °C. The full layer stack of the SHJ solar cells has been described in [21].…”