## 1 Introduction  
Crystalline silicon (c-Si) solar cells have a high conversion efficiency and low-fabrication cost [1; 2; 3; 4]. However, the efficiency of c-Si solar cells is limited by Auger recombination. Recently, c-Si solar cells, composed of ultra-thin films, have attracted considerable attention because such cells generate a higher open-circuit voltage (\(V_{\text{oc}}\)) than cells with thicker films, thereby reducing Auger recombination and increasing the conversion efficiency [5; 6]. However, ultra-thin c-Si solar cells have a low absorption coefficient and, therefore, have a low short-circuit current density (\(J_{\text{sc}}\)). Typically, the conversion efficiency of ultra-thin c-Si solar cells is limited by the trade-off between \(V_{\text{oc}}\) and \(J_{\text{sc}}\). Light management techniques are required to achieve a high \(J_{\text{sc}}\)[7; 8; 9; 10; 11], while maintaining a high \(V_{\text{oc}}\). Silicon nanowire (SiNW) arrays have garnered considerable research interest as light-trapping structures because of their strong light-confinement effect [12; 13; 14]. Accordingly, a SiNW array structure can increase the absorption of a thin absorber layer. Several methods have been proposed for developing SiNW arrays, including laser ablation [15; 16], thermal evaporation [17], chemical vapour deposition [18; 19], reactive-ion etching [20; 21], and metal-assisted chemical etching (MAE) [22; 23; 24; 25]. Among these methods, MAE is widely used because it is simple and cost-effective. In the MAE process, silver (Ag) particles are used as a catalyst to develop large-area aligned SiNW arrays on Si-wafer substrates [26; 27]. The application of nanowires to solar cells has been attempted in several device configurations and materials systems. In particular, the SiNWs demonstrate effective light-trapping performance and can be used in photonic crystals that require precise design. [PERSON] et al., reported numerous simulations, showing that a radial-type SiNW solar cell has potentially greater conversion efficiency than a flat solar cell with the same film thickness [28]. However, the conventional SiNW arrays are generally fabricated on Si-wafer substrates. When researchers deposited SiNWs onto the active layer of a SiNW solar cell, they failed to determine whether the photocurrent originated from the SiNWs or the Si wafer [19; 21; 23]. Therefore, the literature contains no reports of a solar cell structures fabricated only with single-crystalline SiNWs. Because a self-standing SiNW cannot be fabricated, constructing SiNW solar cells, that have been separated from Si-wafer substrates, is difficult. Thus, SiNW arrays have been used as anti-reflection coatings in c-Si solar cells. To develop SiNWs as an active layer for solar cells, new structure and new processes are required. Herein, the SiNW solar cell structure was fabricated on a silicon-on-insulator (SOI) substrate to reduce the effect of bulk c-Si. This facile fabrication process employs electroless Ag plating in conjunction with MAE. For the remaining thin silicon layer, the SiNW length must be controlled to function as a carrier underneath. Herein, the effects of silver nitrate (AgNO\({}_{3}\)) concentration in the solution, that were used in the electroless Ag plating process on the SiNW density and diameter, were investigated. The effects of the etching time of the MAE on the SiNW length, using standard p-type c-Si wafer substrates, were determined, and the morphology and optical properties of the resulting arrays were evaluated. After the SiNW fabrication process was optimised, a solar cell structure was fabricated by depositing an n-type H-doped amorphous Si (a-Si:H) layer onto a p-type SiNW array absorber layer, formed via MAE on the SOI substrate. Table 1 summarizes the SiNW characteristic and its structure in the solar cell between the reported literatures and this study. The length of the SiNW on the Si wafer in this case was <1 \(\upmu\)m [29; 30]. However, when SiNW was used as the doping layer, it was 4\(\upmu\)m long [31; 32].