Abstract
Recently, extensive studies have focused on exploring a variety of silicon (Si) nanostructures among which Si quantum dots (Si QDs) may be applied in all Si tandem solar cells (TSCs) for the time to come. By virtue of its size tunability, the optical bandgap of Si QDs is capable of matching solar spectra in a broad range and thus improving spectral response. In the present work, size-controllable Si QDs are successfully obtained through the formation of Si QDs/SiC multilayers (MLs). According to the optical absorption measurement, the bandgap of Si QDs/SiC MLs shows a red shift to the region of long wavelength when the size of dots increases, well conforming to quantum confinement effect (QCE). Additionally, heterojunction solar cells (HSCs) based on Si QDs/SiC MLs of various sizes are presented and studied, which demonstrates the strong dependence of photovoltaic performance on the size of Si QDs. The measurement of external quantum efficiency (EQE) reveals the contribution of Si QDs to the response and absorption in the ultraviolet–visible (UV-Vis) light range. Furthermore, Si QDs/SiC MLs-based solar cell shows the best power conversion efficiency (PCE) of 10.15% by using nano-patterned Si light trapping substrates.
Highlights
Characterized by abundance, non-pollution, and mature production technology, solar cells based on silicon (Si) have been extensively applied
When a-Si sublayers see an increase in thickness, the Raman peak has a gradual shift towards 520 cm−1, demonstrating that Si quantum dots (Si quantum dots (QDs)) show an increase in size with the increasing thickness of a-Si sublayers
With regard to transmission electron microscopy (TEM) and Raman characterization, Si QDs/SiC multilayered structures are effective in constraining the size of Si QDs during the process of deposition and annealing at high temperature, suggesting that the thickness of a-Si sublayers can be altered with the fabrication method to precisely control the size of Si QDs
Summary
Characterized by abundance, non-pollution, and mature production technology, solar cells based on silicon (Si) have been extensively applied. In the past several years, it was theoretically and experimentally shown that tandem structures were effective in improving the photovoltaic property of solar cells [2,3,4]. Meillaud et al theoretically calculated that two-junction TSCs could reach an efficiency of 42.5% as long as the bandgap of top cell materials was 1.7 eV [5]. The efficiency of three-junction TSCs could reach up to 47.5% in theory, and middle and top materials should have a bandgap of 1.5 eV and 2.0 eV, respectively [6]. Since upper cell materials with suitable bandgap are of critical importance for multi-junction TSCs, numerous semiconductors have been deeply studied, including III–V and II–VI compounds, organic/inorganic perovskite materials, etc. Since upper cell materials with suitable bandgap are of critical importance for multi-junction TSCs, numerous semiconductors have been deeply studied, including III–V and II–VI compounds, organic/inorganic perovskite materials, etc. [7,8,9]
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