# Preparation of Hybrid Molybdenum Disulfide/Single Wall Carbon Nanotube-n-Type Silicon Solar Cells
## 1 Introduction
One limiting factor in the performance of the CNT/Si heterojunctions is the film morphology. Highly ordered, aligned carbon nanotube films have been produced using various techniques [16; 17; 18; 19; 20]. The ordered alignment of the SWCNTs allows a thin, highly transparent, very smooth film to be produced, which does not suffer from the drawbacks of thin films produced via other methods (such as poor contact with the silicon substrate and a poorly formed nanotube network with many electronic charge traps and physical holes in the film). Front-side reflectance detracts significantly from the photocurrent production of photovoltaic devices. Random pyramids in the CNT/Si heterojunction design improve the efficiency [21; 22; 23], as observed in other photovoltaic devices [24], while the use of silicon nanowires has also been investigated by [PERSON] et al. The nanowires dramatically lowered the surface reflectance leading to improved performance [25]. Another approach to reduce the silicon reflectance involved spin coating of a TiO\({}_{2}\) colloid giving a nanoparticulate layer of 50-80 nm in thickness on the surface [26]. In the case of the nanotube/silicon cells, the layer subdued the light reflection significantly to give cell efficiencies above 15% [4]. Recently, [PERSON] et al. investigated the application of molybdenum oxide (MoO\({}_{\text{x}}\)) and zinc oxide (ZnO) as cheap, environmentally friendly antireflection layers [5]. Polymers such as poly(dmiethylsiloxane) (PDMS), [27] polystyrene (PS), [27] poly(methylmethacrylate) (PMMA) [27; 28], or NOA63 [29] have also been examined for their antireflective properties and have the added bonus of providing protection from the environment for added stability in addition to the improved performance. Other work to improve the performance of nanotube/silicon cells has involved putting a layer between the SWCNTs and the silicon. For example, [PERSON] et al. reported a cell design combining a first layer of polyaniline (PANI) and then a second layer of SWCNTs on an n-silicon substrate. The SWCNT/PANI/Si junctions showed a maximum efficiency of 9.7% [30]. The use of other hole transporting materials such as (3\(\mathcal{A}\)-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), [31] 2,2',7,7'-tetrakis(N,N'-di-\(p\)-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD), [32] 4,4'-(naphthalene-2,6-diyl)bis(N,N-bis(4-methoxyphenylyl)aniline) (NAP), and (E)-4'/_A_''-(ethene-1,2-diyl)bis(N,N-bis(4-methoxyphenylyl)-[1'',1''-biphenyl]-4 amine) (BPV) [33] have also been reported. There has been huge interest in developing solar cells using 2D materials. For instance, molybdenum disulfide (MoS\({}_{2}\)) has distinctive optical, photodetection, and electronic characteristics [34]. In this research project, using molybdenum disulfide films, SWCNT suspensions, and hybridised MoS\({}_{2}\) with SWCNTs, the objective was to fabricate solar cells where the n-type semiconductor is the n-type silicon and the p-type semiconductor is the SWCNTs (Figure 1i). Then the molybdenum disulfide was added as an n-type semiconductor to the SWCNT/Si based solar cells to improve the devices' efficiency. The MoS\({}_{2}\) was used to make hybrids of SWCNTs/MoS\({}_{2}\) by filtering different volumes of MoS\({}_{2}\) and SWCNTs at the same time and then attaching this mixed film to the n-type Si (Figure 1 ii). Alternatively, a layered SWCNTs/MoS\({}_{2}\)/n-type Si solar cell was built where first the MoS\({}_{2}\) film is attached to the Si substrate and then a SWCNT film is attached over the MoS\({}_{2}\) film (see Figure 1 iii). Ultimately this means three types of devices will be compared where the films placed over the Si substrate are changing: (1) SWCNT only, (2) hybrid of SWCNT/MoS\({}_{2}\), and (3) a layer of MoS\({}_{2}\) followed by a layer of SWCNTs. Previous work has produced the Si/MoS\({}_{2}\)/SWCNT layered structure (see Figure 1 iii) [35]. Other work using 2D materials has often made hybrids of the 2D materials and the SWCNTs [36; 37].