# Innovative Approaches to Semi-Transparent Perovskite Solar Cells
## 3 Transparent Electrodes for ST-PSCs
In this method, they utilized a linear-facing target sputtering system (LFTS) and a deposited ITO (10 wt% SnO\({}_{2}\)-doped In\({}_{2}\)O\({}_{3}\)) and IZO (10 wt% ZnO-doped In\({}_{2}\)O\({}_{3}\)) targets at a constant DC power. The resulting IZTO top electrode was utilized for fabricating ST-PSCs and attained a PCE of 12.85%, similar to that of an Ag-electrode-based device of 13.48%. Furthermore, by altering the thickness of the perovskite layer, a PCE of 8.30% was achieved at an AVT of 33.9%. As a result, they suggested an advanced method to increase the conductivity of ITO and reduce damage to perovskite [66]. Furthermore, [PERSON] et al. introduced hydrogen into In\({}_{2}\)O\({}_{3}\) as a dopant, which was applied to ST-PSCs with a particular FTO structure (FTO/ZnO/PCBM/CH\({}_{3}\)NH\({}_{3}\)PbI\({}_{3}\)/Spiro-MeTAD/MoO\({}_{3}\)/H-doped In\({}_{2}\)O\({}_{3}\) (In\({}_{2}\)O\({}_{3}\):H)); In\({}_{2}\)O\({}_{3}\):H sputtered at room temperature without post-annealing generated a hysteresis-free ST-PSC with good efficiency [50]. In a recent approach, [PERSON] et al. engineered the top electrode using gallium and titanium-doped indium oxide (IO:GT) in between the top electrode and electron transport layer. They modified the work function to narrow for enhancing the charge transport and reducing the Schottky barrier. The modified devices exhibited a certified PCE of 17.53% with a 21.9% AVT with excellent air stability. Furthermore, four-terminal perovskite-perovskite solar cells exhibited a high PCE of 23.35% [67]. Ultra-thin metal films also serve as an effective approach for TEs, owing to their superior conductivity and transmittance [34; 68; 69; 70; 71; 72; 73; 74]. Similar to other TEs, it is important to carefully manage the coating thickness to produce appropriate conductivity while maintaining high transmittance for optimal performance, even in thin metal films. Accordingly, a deposition technique using a wet or seed layer for adjusting the thickness of a metal film has been developed; organic and inorganic materials with considerable surface energy, such as polymers [75; 70], small molecules [76; 77; 71; 72; 73; 74] and metal oxides [76; 78; 79], have been used for the wet layer and the seed layer. [PERSON] et al. used the wet deposition method, which created perovskite grids with different dimensions. The transparency of the perovskite film was attained by controlling the perovskite solution concentration and mesh openings. As a result, ST-PSC showed a transparency between 20 to 70% and achieved a PCE of 5% at 20% transparency [68]. For other approaches, instead of a primary metal thin film, to increase the conductivity and transmittance of metal-thin-film-based electrodes, sandwich-structured electrodes using dielectric material/metal/dielectric material (DMD)have been studied [30; 37; 69; 72; 74; 76; 80]. The main principle to utilize DMD structures relies on interference phenomena created by the two dielectric layers to improve transmission through the thin metal film. The DMD TE composed of a MoO\({}_{3}\)-Au-MoO\({}_{3}\) stack, as seen in (Figure 3a), was utilized by [PERSON] et al. to fabricate ST-PSCs [30]. The MoO\({}_{3}\)-Au-MoO\({}_{3}\) TE showed improved transparency and conductivity, attaining a PCE of 13.6% with a 7% AVT (Figure 3b). On a similar note, [PERSON] et al. constructed ST-PSCs with SnO\({}_{\text{x}}\)/Ag/SnO\({}_{\text{x}}\) as the TE. The SnO\({}_{\text{x}}\) worked as a permeation barrier under the Ag thin film and as a seed layer, inhibiting Ag from reacting with halides in perovskite. In addition, the upper SnO\({}_{\text{x}}\) acted as a capping layer to prevent Ag from reacting to moisture and oxygen and to increase stability. The ST-PSC fabricated with this method showed a PCE higher than 11% with a 70% AVT in the near-infrared region and a 29% AVT, along with excellent stability in an ambient atmosphere with an elevated temperature [69].