New progress in the fabrication of n–i–p micromorph solar cells for opaque substrates

Abstract

a b s t r a c tIn this paper, we investigate tandem amorphous/microcrystalline silicon solar cells with asymmetric intermediate reflectors grown in the n-i-p substrate configuration. We compare different types of substrates with respect to their light-trapping properties as well as their influence on the growth of single-junction microcrystalline cells. Our most promising back reflector combines a textured zinc oxide film grown by low-pressure chemical vapor deposition, a silver film for reflection, and a zinc oxide buffer layer. Grown on this substrate, microcrystalline cells exhibit excellent response in the infrared while keeping high open-circuit voltage and fill factor, leading to efficiencies of up to 10.0%. After optimizing the morphology of the asymmetric intermediate reflector, we achieve an n-i-p micromorph solar cell stabilized efficiency of 11.6%, using 270 nm and 1.7 mm of silicon for the absorber layer of the amorphous top cell and the microcrystalline bottom cell, respectively. Using this original device architecture, we reach efficiencies close to those of state-of-the-art n-i-p and p-i-n micromorph devices, demonstrating a promising route to deposit high-efficiency thin-film silicon solar cells on opaque substrates.

10.5% efficient polymer and amorphous silicon hybrid tandem photovoltaic cell

“…1c. We have attempted to form series connection of these two optimized cells with minimized series resistance at the junction, which is essential to obtain the best-performing tandem devices 3,[9][10][11][12][13][14] . Typically in thin-film tandem cells, ultrathin doped layers are employed to form tunnel junctions between the sub-cells with extremely high doping 2,13,14 .…”

“…We have attempted to form series connection of these two optimized cells with minimized series resistance at the junction, which is essential to obtain the best-performing tandem devices 3,[9][10][11][12][13][14] . Typically in thin-film tandem cells, ultrathin doped layers are employed to form tunnel junctions between the sub-cells with extremely high doping 2,13,14 . Although ultrathin heavily n-doped a-Si:H film can be obtained, hole collection layer (HCL) for polymer cells such as MoO 3 sulfonate (PEDOT:PSS) can be neither ultrathin nor highly doped [20][21][22] .…”

“…These efficiencies of polymer and a-Si:H cells are not acceptable for achieving grid parity. To maximize the efficiency of such kind of low-efficiency solar cells, a solar cell made by stacking the multiple absorbers with complementary absorption spectra, so called a tandem cell, is considered as one of the most effective approaches 3,[9][10][11][12][13][14] .…”

Tuning the porosity of zinc oxide electrodes: from dense to nanopillar films

“…The thickness of the films varied between 0.65 and 1.2 μm. a-Si:H layers were deposited in the n-i-p configuration by plasma-enhanced chemical vapor deposition [19] while the front electrode was made of either the dense or dense/nanopillar film stacks as showed below (cfr. figure 5).…”

Inorganic photovoltaics – Planar and nanostructured devices

“…In the standard cell process, the metal impurities can be reduced and even totally 454 deactivated when the wafers are submitted to the diffusion process, due to gettering effects 455 (explained in Sec. 2.3.3.).…”