# Developments on Perovskite Solar Cells (PSCs): A Critical Review
## 4 Perovskite Solar Cell Device Architecture
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Device** & **Type** & **V\({}_{\rm oc}\)** & **J\({}_{\rm sc}\)** & **FF** & **PCE** & **Year** & **Ref.** \\ \hline Single-halide & FTO/m-TiO\({}_{2}\)/MAPbI\({}_{3-}\)/LiBr \({}_{3}\)/Pt-FTO & 0.96 & 5.57 & 59.0 & 3.13 & 2009 & [2] \\ PSC & FTO/m-TiO\({}_{2}\)/MAPbI\({}_{3-}\)/HTM/LiI\({}_{2}\)/Pt-FTO & 0.61 & 11.0 & 57.0 & 3.81 & 2009 & [2] \\ \hline  & ITO/PCBM/MAPbI\({}_{3-}\)Cl\({}_{x}\)/Spiro-MeOTAD/ & 0.97 & 17.9 & 70.0 & 12.2 & 2013 & [20] \\ Mixed-halide & FTO/TiO\({}_{2}\)/MAPbI\({}_{3-}\)Cl\({}_{x}\)/PTAA/Au & 1.10 & 21.4 & 77.6 & 18.3 & 2016 & [40] \\ PSC & ITO/ETM/MAPbI\({}_{3-}\)Cl\({}_{x}\)/JTM/ & 1.05 & 10.01 & 70.0 & 8.7 & 2014 & [41] \\  & metal contact & & & & & & \\ \hline  & FTO/co-TiO\({}_{2}\)/mp- & & & & & & \\  & TiO\({}_{2}\)/(PAPbI\({}_{3}\))\({}_{0.85}\)(MAPbBr\({}_{3}\))\({}_{0.15}\)/Spiro- & 1.15 & 22.7 & 76.0 & 20.2 & 2016 & [29] \\ Mixed cations & FTO/c-TiO\({}_{2}\)/m-TiO\({}_{2}\)/C\({}_{x}\)/FA/MA/Spiro- & 1.14 & 23.6 & 77 & 20.8 & 2017 & [42] \\  & (Rb\({}_{0.1}\)Cs\({}_{0.5}\)FA\({}_{0.85}\))/Pb(1\({}_{x}\)Br\({}_{x}\)) & 1.15 & 22.2 & 73.0 & 18.7 & 2016 & [43] \\ \hline Metal Oxide & ITO/TiO\({}_{2}\)/MAPbI\({}_{3-}\)Cl\({}_{x}\)/Spiro-MeOTAD/Ag & 0.95 & 21.4 & 60.0 & 12.2 & 2014 & [44] \\  & ITO/ZnO/MAPbI\({}_{3-}\)/Spiro-MeOTAD/Au & 0.87 & 19.2 & 67.6 & 11.3 & 2016 & [45] \\  & ITO/NiO/MAPbI\({}_{3-}\)Cl\({}_{x}\)/PCBM/Al (inverted) & 0.97 & 15.89 & 57 & 8.78 & 2014 & [46] \\ \hline  & FTO/ETM/FA\({}_{0.8}\)MA\({}_{0.5}\)/Spiro-MeOTAD/Au & 1.16 & 21.5 & 73.0 & 18.1 & 2017 & [47] \\ HTM & ITO/PEODF:SS/MAPbI\({}_{3-}\)Cl\({}_{x}\)/PCBM/Ag & 1.11 & 20.11 & 80.6 & 16.5 & 2018 & [48] \\  & (inverted) & & & & & & \\  & FTO/c-TiO\({}_{2}\)/m-TiO\({}_{2}\)/MAPbI\({}_{3}\)/TTF/Ag & 0.86 & 19.9 & 64.4 & 11.0 & 2012 & [49] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Types of PSCs with device architecture “TCO/ETM/Perovskite layer/HTM/metal contact varied by the perovskite layer, ETM and HTM [5; 20; 30; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52]. Figure 5: (**a**) IPCE and (**b**) I–V curve for MAPbBr\({}_{3}\) (solid line) and MAPbI\({}_{3}\) (solid line) [5]. Further to the designing of ABX\({}_{3}\), processing conditions such as thermal annealing, ageing, doping, moisture and solvent treatment strategies are used to optimize device performance during PSC fabrication. [PERSON] (2016) studied the effect of ageing (a device placed in the dark at room temperature) on the diffusion length and bandgap energy of mixed MAPb(I\({}_{1\times}\)Br\({}_{x}\))\({}_{3}\) halide perovskite. Figure 7a shows a plot of the mixed perovskite diffusion length L (nm) against bandgap energy (eV) values; the insert images are the aged PSC thin films arranged according to their bandgap energies; the white and black dots present corresponding diffusion length and bandgap values for aged and non-aged PSCs films, respectively. It is noted in both cases that the bandgap structure is tuned by varying the bromine (Br) and iodide (I) weight fractions. Bandgap values in the thin films increase with increasing Br content. A distinctive phase change is observed by the color change towards high bandgap values from black to yellow, indicating that the devices can be optimized to absorb specific regions in the solar spectrum. The aged film at \(\sim\)1.8 eV recorded the highest diffusion length, double of the non-aged films. This study, therefore, shows that the application of processing conditions on either single- or mixed-halide perovskite thin films offers the ability to fine-tune the resulting perovskite optical properties for better and desired performances [28; 53]. Figure 6: (a) Dip–coating solution preparation method for the perovskite films and the corresponding surface morphologies in PbI\({}_{2}\), MAPbI\({}_{3\times}\)Cl\({}_{x}\), and/or MAPbI\({}_{3}\) thin films.