## 5 The Architecture Design and Combinations of New Devices
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Structure**} & \(\boldsymbol{V_{\text{cc}}}\) & \(\boldsymbol{J_{\text{sc}}}\) & \(\boldsymbol{F(\%)}\) & \multirow{2}{*}{**PCE (\%)**} & \multicolumn{2}{c}{**Published Year**} & \multirow{2}{*}{**Ref**} \\  & **(V)** & & & & & \\ \hline ITO/CdTe/ZnO/Al & 0.59 & 20.70 & 56.0 & 6.9 & 2011 & [26] \\ ITO/CdTe/ZnO/Al & 0.61 & 21.20 & 60.0 & 7.7 & 2014 & [34] \\ ITO/CdTe/ZnO/Al & 0.686 & 25.50 & 64.7 & 11.3 & 2014 & [33] \\ ITO/CdTe/In: ZnO/Al & 0.69 & 21.20 & 67.0 & 9.8 & 2014 & [32] \\ ITO/CdTe/In: ZnO/Al & 0.684 & 25.80 & 71.0 & 12.3 & 2014 & [29] \\ \hline ITO/CdTe/CdSe/Al & 0.42 & 16.90 & 36.0 & 2.6 & 2009 & [23] \\ ITO/CdTe/CdSe/Al & 0.429 & 16.30 & 37.4 & 3.02 & 2010 & [58] \\ ITO/CdTe/CdSe/Al & 0.61 & 20.3 & 57.0 & 7.1 & 2012 & [45] \\ ITO/CdSe/CdTe/Cr/Au & 0.593 & 7.2 & 43.7 & 1.9 & 2014 & [31] \\ ITO/CdSe/CdTe/Au & 0.56 & 17.2 & 40.1 & 3.75 & 2014 & [59] \\ ITO/ZnO/CdSe/CdTe/Au & 0.65 & 15.28 & 58.5 & 5.81 & 2015 & [46] \\ ITO/ZnO/CdSe/CdTe:CdSe/CdTe/Au & 0.6 & 21.06 & 49.5 & 6.25 & 2016 & [60] \\ ITO/ZnO/CdSe\({}_{\text{x}}\)Te\({}_{\text{1-x}}\)CdTe/MoO\({}_{\text{x}}\)/Au & 0.67 & 19.70 & 48.3 & 6.37 & 2017 & [61] \\ ITO/ZnO/CdSe/CdTe/Si-TPA/Au & 0.66 & 23.38 & 54.05 & 8.34 & 2018 & [57] \\ \hline ITO/TiO\({}_{\text{2}}\)/CdTe/spiro-OMeTAD/Au & 0.71 & 15.82 & 45.2 & 5.16 & 2015 & [54] \\ ITO/TiO/CdTe-CdS/MoO/Au & 0.564 & 17.8 & 57.1 & 5.73 & 2015 & [62] \\ ITO/ZnO/Sb:TiO\({}_{\text{2}}\)/CdTe/Au & 0.7 & 14.65 & 34.44 & 3.53 & 2017 & [51] \\ FTO/TiO\({}_{\text{2}}\)/CdS/CdTe/Au & 0.83 & 16.02 & 30.5 & 4.05 & 2018 & [63] \\ \hline ITO/ZnO-In/CdS/CdTe/MoO\({}_{\text{x}}\)/Ag & 0.49 & 17.5 & 43.5 & 3.73 & 2013 & [38] \\ Glass/Mo/Cu\({}_{\text{x}}\)Te/CdTe/CdS/ZnO/Al & 0.679 & 15.9 & 54.9 & 5.94 & 2014 & [33] \\ FTO/SnO\({}_{\text{2}}\)/CdS/CdTe/ZnTe/Ti & 0.709 & 18.3 & 51.3 & 6.66 & 2014 & [33] \\ ITO/SnO\({}_{\text{4}}\)/CdTe-CdS/P3 KT/MoO/Au & 0.54 & 19.5 & 56.0 & 5.9 & 2017 & [55] \\ ITO/ZnO/CdS/CdTe/MoO\({}_{\text{y}}\)/Au & 0.56 & 17.26 & 52.84 & 5.14 & 2018 & [25] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Selected performance parameters of CdTe NC solar cells fabricated via solution process. CdTe-CdS NC solar cells (Figure 3e) [38]. The performance of alloy NC solar cells is also found to be related to the thickness of active layer (Figure 3f), the device architecture, and the quantity of alloy active layers used. In optimized device structure of ITO/ZnO/ CdSe\({}_{0.8}\)Te\({}_{0.2}\)/CdSe\({}_{0.2}\)Te\({}_{0.8}\)/CdTe/MoO\({}_{\text{A}}\)Au, the series resistance (\(R_{\text{s}}\)) is decreased and the shunt resistance (\(R_{\text{sh}}\)) increased when comparing to device with structure of ITO/ZnO/CdSe\({}_{0.2}\)Te\({}_{0.8}\)/CdTe/MoO\({}_{\text{A}}\)Au, which results in a high PCE of 6.37% (4.03% for controlled device) [61]. Introducing other semiconductor NC or organic semiconductor materials to build tandem solar cells is another way to further improve the performance of CdTe NC solar cells. PbS quantum dots are important semiconductor materials for photovoltaic application as the band gap can be tuned from the bulk value (0.41 eV) up to \(\sim\)1.6 eV by controlling the grain size [65; 66]. The efficiency of PbS quantum  
Figure 3: (**a**) Schematic of the vertically-graded bandgap structure of ITO/ZnO/CdSe/CdSe\({}_{\text{x}}\)Te\({}_{1\text{-}}\)/ CdTe/MoO\({}_{\text{A}}\)/Au, (**b**) energy diagram of the above devices, _J-V_ characteristics of the above devices (**c**) under light and (**d**) dark, (**e**) EQE properties of the devices, and (**f**) the PCE of NC solar cells with different thickness of CdSe\({}_{0.2}\)Te\({}_{0.8}\) alloy NC films [64]. dot solar cells has improved from \(\sim\)0.1% to \(\sim\)11% in recent years [4]. As the optical absorption of PbS quantum dots can be extended to the infrared region, coupled with low temperature device fabrication, all these merits make PbS quantum dots solar cells (CQDs) suitable for application in tandem cells. [PERSON] et al.