Abstract
The rise in the power conversion efficiency (PCE) of perovskite solar cells has triggered enormous interest in perovskite-based tandem photovoltaics. One key challenge is to achieve high transmission of low energy photons into the bottom cell. Here, nanostructured front electrodes for 4-terminal perovskite/crystalline-silicon (perovskite/c-Si) tandem solar cells are developed by conformal deposition of indium tin oxide (ITO) on self-assembled polystyrene nanopillars. The nanostructured ITO is optimized for reduced reflection and increased transmission with a tradeoff in increased sheet resistance. In the optimum case, the nanostructured ITO electrodes enhance the transmittance by ∼7% (relative) compared to planar references. Perovskite/c-Si tandem devices with nanostructured ITO exhibit enhanced short-circuit current density (2.9 mA/cm2 absolute) and PCE (1.7% absolute) in the bottom c-Si solar cell compared to the reference. The improved light in-coupling is more pronounced for elevated angle of incidence. Energy yield enhancement up to ∼10% (relative) is achieved for perovskite/c-Si tandem architecture with the nanostructured ITO electrodes. It is also shown that these nanostructured ITO electrodes are also compatible with various other perovskite-based tandem architectures and bear the potential to improve the PCE up to 27.0%.
Highlights
During the last decade, organo-metal halide perovskite solar cells (PSCs) have witnessed a remarkable enhancement in the power conversion efficiency (PCE), surpassing 25% to date [1]
The series resistance (RS) in the J-V characteristic of the PSC is only slightly affected (RS of planar indium tin oxide (ITO)-PSC: 70.2 Ω and nanostructured ITO (NS ITO)-PSC: 81.4 Ω), indicating that the decreased conductivity is not too severe. These results suggest that NS ITO electrodes are very promising optically for the application in PSCs and tandem photovoltaics
NS ITO electrodes for perovskite/c-Si tandem solar cells are developed by sputtering ITO on self-assembled polystyrene nanopillars
Summary
Organo-metal halide perovskite solar cells (PSCs) have witnessed a remarkable enhancement in the power conversion efficiency (PCE), surpassing 25% to date [1]. Micron-scale textures at the front side of two-terminal (2 T) and four-terminal (4 T) device architectures have demonstrated to reduce the reflection losses, improving the light in-coupling and light trapping as well as enhancing the transmission of the low energy photons through the top solar cell into the bottom solar cell [8,9,14,19,20,21,22]. Mostly employed so far in 4 T architectures having front planar surfaces, and compatible with 2 T, makes use of retroreflector-inspired micron-scale pyramidal structures or micro-textured foils at the front side of the transparent cover of the device [8,9,20,22] These micro-textures reduce the reflection losses of the incident light by multiple interactions with the textured surface, which increases the probability for light in-coupling [23,24]. The 4 T PSC/c-Si tandem solar cells using nanostructured front electrodes show improved angular stability of light in-coupling, leading to an enhanced annual energy yield
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