## 3 Results and Discussion
The various HTM thicknesses, all at an annealing temperature of 600 \({}^{\circ}\)C, were compared here under 100 mW/cm\({}^{2}\) illumination (AM 1.5G). At least six cell samples of each type have been fabricated, with the performance deviation \(\sim\)5%. Additionally, Table 1 summarizes the characteristic parameters of the novel solar cells at the various HTM thicknesses using a 600 \({}^{\circ}\)C annealing temperature. The solar cells' open-circuit voltage could be increased from 0.96 to 1.02 V, with the CuIn\({}_{1-x}\)Ga\({}_{x}\)Se\({}_{2}\) HTM film from 100 to 300 nm. The short-circuit current value also increased from 20.4 to 20.9 mA/cm\({}^{2}\). The device fill factor values were slightly diminished from 67.4% to 65.6%. The photovoltaic device PCE ranged from 13.2% to 14.2%. In addition, the device series-resistance was decreased from 16.9 to 15.8 \(\Omega\). The output power Pmax effect values increased from 1.32 mW to 1.42 mW. Figure 6: Tauc plot for measuring the energy band gap for CuIn\({}_{1-x}\)Ga\({}_{x}\)Se\({}_{2}\) HTM grown on a bi-layer Mo/FTO glass substrate. The red line was used to extrapolate the band-gap. Figure 7: J–V curves of MAPbI\({}_{3}\) perovskite solar cells with ultra-thin CuIn\({}_{1-x}\)Ga\({}_{x}\)Se\({}_{2}\)HTM nano-structures on a bi-layer Mo/FTO glass substrate, using various HTM thicknesses with a 600 \({}^{\circ}\)C thermal annealing temperature. Measurement under 100 mW/cm\({}^{2}\) illumination (AM 1.5G). Furthermore, the fill factor has been defined as the ratio of the output power Pmax to the device open-circuit voltage and short-circuit current at the maximum electric power output. This is the maximum power of the rectangle in the current-voltage characteristic curve. In accordance with the current-density voltage curve and the PCE value, it has been suggested that the optimal thickness of the CuIn\({}_{1-\mathrm{X}}\)Ga\({}_{\mathrm{x}}\)Se\({}_{2}\) hole-transporting film layer is at \(\sim\)200 nm. This sample exhibited a slightly higher open-circuit voltage along with the lowest device series-resistance. In this study, it has been desired to develop ultra-thin HTM layers for solar cell applications. The CIGS film quality has been improved and the HTM layer thickness was decreased. In fact, the 300 nm sample also exhibited a reasonably good PSC performance. On the other hand, when the CIGS layer was tried at a thickness below 100 nm (such as 30-50 nm, not shown in this report), not only was the PSC performance was degraded but also the deviation increased appreciably. An ultra-thin CuIn\({}_{1-\mathrm{X}}\)Ga\({}_{\mathrm{x}}\)Se\({}_{2}\)HTM (<400 nm) has been deposited between the MAPbI\({}_{3}\) active absorber material and the bi-layer Mo metal-electrode to promote carrier transport, leading to an improved device witha goodohmic-contact. Additionally, innovative structures of bi-layer Mo films were deposited onto FTO/glass substrates. Eventually, Figure 8 shows the ultra-thin CuIn\({}_{1-\mathrm{X}}\)Ga\({}_{\mathrm{x}}\)Se\({}_{2}\) hole-transporting material detailed investigation on the compositional dependence of the Raman spectra, grown on a bi-layer Mo/FTO glass substrate. In this work, the CuIn\({}_{1-\mathrm{X}}\)Ga\({}_{\mathrm{x}}\)Se\({}_{2}\) HTM film exhibited dominant spectra with an intense Raman scattering peak at 174 cm\({}^{-1}\), corresponding to the optical phonon mode that was characteristic of the chalcopyrite nano-crystals and nano-structures. The Raman intensities at 174 cm\({}^{-1}\), 214 cm\({}^{-1}\) and 240 cm\({}^{-1}\) were slightly increased while increasing the annealing temperature. The CuIn\({}_{1-\mathrm{X}}\)Ga\({}_{\mathrm{x}}\)Se\({}_{2}\) HTM crystal orientation could be found from the polarization of Raman-scattered light with respect to the laser light if the crystal structure's point group was known. Figure 9 shows the device measured external quantum efficiency (EQE) curve results due to optical modification with CuIn\({}_{1-\mathrm{X}}\)Ga\({}_{\mathrm{x}}\)Se\({}_{2}\) hole-transporting material. The spectra