## 3 Results and Discussions
This IPCE increase is assigned to the magnified light scattering effect [8; 9; 10]. However, the sole Au integrated solar cell reduces IPCE for photons possessing energy less than 2 eV, resulting from the back-scattering effect associated with Au NPs [15; 16; 17; 18]. Meanwhile, the integration of cells with Au/QD layer further intensifies the J\({}_{\text{SC}}\), from 14.86 mA/cm\({}^{2}\) to 19.56 mA/cm\({}^{2}\), which is strongly suggested by the elevated IPCE value for broad spectrum. The hybrid Au/QDs structure overcomes the limit of sole embedded-Au NPs by the downshifting effect of QDs. The embedded hybrid structure-based solar cell provides an overall improved IPCE of 15% compared to bare Si-based solar cells. Figure 3: (**a**) Normalized absorption spectra of Au NPs. (**b**) Absorption and emission spectra of CdSe/ZnS QDs. (**c**) Absorption spectra of QDs-528 nm individually and QDs-Au NPs conjugates. The photogeneration and separation process in the solar cell are studied by the proposed energy band diagram, as shown in Figure 4c. The work function of heavily doped n-type silicon with the resistivity of 1-10 \(\Omega\)cm is reported as \(\Phi_{\rm Si}\) = 4.58 eV, and the bandgap is about 1.11 eV [32, 33]. The work function of Au and Ti (\(\Phi_{\rm Au}\) & \(\Phi_{\rm Ti}\)) are 5.1 eV and 3.84 eV, respectively [34]. The higher work function of Au compared to n-Si results in the formation of built-in potential at the Au/n-Si interface. This built-in potential imposes the potential barrier height to the free electrons inside n-Si that leads to the formation of the Schottky junction. In addition, \(\Phi_{\rm Ti}\) is smaller than \(\Phi_{\rm Si}\) so that the Ohmic contact forms between Ti and n-Si. Under the light illuminating conditions, the -hole (e-h) pairs are generated by the photon absorption process. This includes two simultaneously interacting light procedures of Si, including direct light-source absorption and QDs induced light emission. The formed electric field as Schottky interface immediately separates the photo generated e\({}^{-}\)/h\({}^{+}\) pairs. The separated carriers are swept away from the Au/Si junction under the drift mechanism to selective contact (electron to Ti and hole to Au); therefore, the photo-induced power is delivered to the external circuit. The enhanced performance of solar cells attributes to the synergetic effects, consisting of plasmonic effect and QDs downshifting. To optimize the impact of Au NPs incorporated with QDs on the devices, three different sizes of prepared Au NPs were employed. The variation of photovoltaic parameters including J\({}_{\rm SC}\), V\({}_{\rm OC}\), FF, and \(\eta\) is described in Figure 5. It is observed patently that the smaller Au NPs diameter induced more enhancement in cell performance. In general, Au NPs 3 with the smallest size of 13.2 nm has the greatest effect on the Si-based Schottky solar cell performance. Specifically, FF and \(\eta\) increased up to 10% and 28%, respectively. The series (R\({}_{\rm S}\)) and shunt resistance (R\({}_{\rm SH}\)) are extracted from the dark J-V profile of the devices, presented by Figure 5c. After coating Au/QDs, the R\({}_{\rm S}\) increased from 1.001 \(\Omega\) to 1.766 \(\Omega\), and the R\({}_{\rm SH}\) decreased from 595 \(\Omega\) to 548 \(\Omega\). The observed resistance variation is negligible; therefore, the improved solar cell performance was primarily governed by the optical effect of Au/QDs hybrid structures. The solar cell parameters with Au NPs 3 and QDs are mentioned thoroughly in Table 1. As discussed, Au NPs 3 implies the most monodisperse  
Figure 4: (**a**) Current density versus voltage curves. (**b**) Incident photon to current conversion efficiency (IPCE) spectra of all devices. (**c**) Energy band diagram at the equilibrium condition. spherical particles and the highest surface coverage on the substrate among three particle sizes, thus contributing significantly to enhancing solar cell performance [35; 36].