The enhanced efficiency of the crystalline silicon (c-Si) with nanopillar arrays (NPAs) solar cell by quantum dots (QDs) was demonstrated. The device with CdS quantum dots shows the higher power conversion efficiency about 33%.
SummaryCurrently, mono and multicrystalline silicon (Si) solar cells have been developed for over decade. The main reason is no pollution, stable conversion efficiency, mature of processing, but Si-based solar cells still exist many problem to reach high efficiency. Especially, an incident light could be lead to optics of Fresnel reflection in the high reflective index of the Si material and air between, which severely limits the performance of Si-based optoelectronic devices, particularly for solar cells, displays, and light sensors [1,2]. In order to reduce Fresnel reflection in the solar cells, an effective mono and multi-antireflective coatings (ARCs) have been developed [3]. Therefore, to fabricate the multilayer ARCs in the solar cells not only need expensive equipment but also need high-vacuum deposition, material selection, and layer thickness control of conditions.Consequently, some research has develop sub-wavelength structures to improve cell efficiency, such as nanowire or nanotips [4,5], and it is more stable and enduring than surface coatings since only one material is involved. The basic purpose of this technique is to introduce a gradient refractive index layer between air and the substrate material by the spatial profile of nanostructures [6,7]. However, most of the nanostructures suggest a tapered profile with sharp tips which may not be preferred in solar cells due to considerable surface states that trap photo-generated carriers. In addition, a large part of high-energy photons is lost as heat through phonon scattering, resulting in limitation of power conversion efficiency of Si solar cell, known as thermal or quantum loss. Especially, it is appear that the ultraviolet (UV) part of the solar spectrum cannot be used by Si solar cells.In this work, we investigate a method by combining the c-Si NPAs solar cell with CdS QDs together, which improves the power conversion efficiency by nearly 33%, compared with the c-Si NPAs solar cell without CdS QDs reference, which was confirmed by the photovoltaic I-V characteristics and the quantum efficiency measurement. It is found that with CdS QDs solar cell can improve cell efficiency, especially in the short-circuit current and fill-factor. Based on the spectral response and optical measurement, we demonstrate that CdS QDs not only have the capability for photon down-conversion in ultraviolet region but also serve as antireflection coating and conductivity for the improvement of Si-based solar cell efficiency.In this experiment, we use colloidal lithography method to fabricate c-Si NPAs solar cell. As schematically illustrated in Fig. 1(a), a monolayer of self-assembled polystyrene (PS) nanospheres with a plurality of 10 wt% was spin-cast onto the surface of a p-type c-Si substrate. A nearly-close-packed PS nanospheres monolayer wa...