# Developments on Perovskite Solar Cells (PSCs): A Critical Review
###### Abstract  
This review provides detailed information on perovskite solar cell device background and monitors stepwise scientific efforts applied to improve device performance with time. The work reviews previous studies and the latest developments in the perovskite crystal structure, electronic structure, device architecture, fabrication methods, and challenges. Advantages, such as easy bandgap tunability, low charge recombination rates, and low fabrication cost, are among the topics discussed. Some of the most important elements highlighted in this review are concerns regarding commercialization and prototyping. Perovskite solar cells are generally still lab-based devices suffering from drawbacks such as device intrinsic and extrinsic instabilities and rising environmental concerns due to the use of the toxic inorganic lead (Pb) element in the perovskite (ABX) light-active material. Some interesting recommendations and possible future perspectives are well articulated. perovskite solar cells; chemical stability; material toxicity; device structure; efficiency +
Footnote †: journal: Applied  
ability of the cell; hence, DSSCs are low-efficiency cells. [PERSON] (2009) studied the PV effect in a photoelectrochemical (PEC) dye-sensitized cell by replacing the dye organic molecules with organic-inorganic halide perovskite molecules such as CH\({}_{3}\)NH\({}_{3}\)PbBr\({}_{3}\) (MAPbBr\({}_{3}\)) and CH\({}_{3}\)NH\({}_{3}\)PbI\({}_{3}\) (MAPbI\({}_{3}\)) and registered power conversion efficiencies (PCE) of 3.1% and 3.8%, respectively [5]. Although perovskites show good PV properties, including optical, excitonic, and electrical conductivity, the above unfavorable low efficiencies were attributed to the dissolution of the perovskite material by the liquid electrolyte [11]. Attempts have been made to stabilize the crystalline perovskite material in DSSCs. [PERSON] (2009) reported an increase in PCE of lead halide perovskites, while many researchers focused on quantum dot sensitized solar cells (QDSSCs) using inorganic metal chalcogenides sensitizers such as PbS, CdSe, and CdS as light-absorbing materials, exhibiting intense bandgap light absorption [12; 13; 14]. However, these quantum dot cells suffered from low efficiencies between 1.2 and 6.4% due to charge recombinations at the interface and chemical instability. To overcome these challenges, the MAPbI\({}_{3}\) perovskite materials were explored as quantum dots in PECs and an increase to 6.5% in PCE in PSCs was achieved [15]. To further increase efficiencies, [PERSON] (2005) proposed the use of hole-transporting materials (HTMs) in DSSCs to eliminate the drawbacks caused by liquid electrolytes in PECs. In a later study, [PERSON] (2012) developed a 10% PCE solid-state PSC device using Spiro-MeOTAD HTM in a perovskite-sensitized solar cell device [16; 17]. Device fabrication of a solid-state PSC consists of a perovskite precursor solution deposition between spaces of mesoporous titanium dioxide (TiO\({}_{2}\)), thin-film on a transparent conductive oxide (TCO) substrate, forming a ABX\({}_{3}\) perovskite layer by an ordered ion agglomeration process, then followed by Spiro-MeOTAD (HTM) deposition, resulting in devices reaching efficiencies of up to 9.7% (see Figure 1a,b). The use of mixed-halide perovskite crystals such as MAPbI\({}_{3-x}\)Cl\({}_{x}\) helps avoid the dissolution of the perovskite material by the Spiro-MeOTAD-disssolving solvents during the deposition [18; 19]. It is further found that the use of insulating mesoporous aluminium oxide (Al\({}_{2}\)O\({}_{3}\)) instead of mesoporous TiO\({}_{2}\) results in better PCE. The Al\({}_{2}\)O\({}_{3}\) appears to act as a structural scaffold in the perovskite material, demonstrating that the ABX\({}_{3}\) perovskite crystal structure contributes to the electron transport, hence, demonstrating devices with high charge collection (see Figure 1c [17; 20; 21].