Unlike fossil fuels, the sun is an inexhaustible energy source that delivers more energy to the earth in 1 h than the entire planet consumes in one year. Energy can be harvested from the sun using photovoltaics (PV) and stored (e.g., batteries), meaning solar energy can be used as and when required. [3,4] Currently, the commercial PV market is dominated by single-junction crystalline silicon (c-Si) PV which deliver power conversion efficiencies (PCE) of over 26% under 1 Sun illumination (AM 1.5 standard). [5,6] Despite their high efficiencies, the fabrication of c-Si PV is nontrivial and lacks electronic tunability. Furthermore, the record efficiency for c-Si PV is 26.7% [5] which is very close to the theoretical limit of 29.4%. [7] This clearly indicates that c-Si PV is a mature technology and there is limited room for improvement. [8] Over the past two decades, third-generation solar cells such as dye-sensitized solar cells, [9,10] quantum dot solar cells, [11,12] organic solar cells, [13,14] and perovskite solar cells (PSCs) [15,16] have been developed as alternatives to c-Si technologies. Of these third-generation solar cells, single-junction PSCs have generated significant attention due to their intense visible to near-infrared absorptivity, [16-18] long diffusion lengths of the charge carriers, [19,20] high efficiency, [21,22] electronic and physical tunability, [23,24] and low manufacturing costs. [25,26] After the first report by Miyasaka's group in 2009, [27] the PCE for single junction devices increased considerably from 3.8% to 25.2%, [27,28] making it the fastest advancing PV technology to date. This has uniquely placed PSCs as the frontrunner technology to potentially replace or coexist with c-Si PV. The term "perovskite" refers to a group of compounds that share the same lattice structure as calcium titanium oxide (CaTiO 3). All PV perovskite materials have the general chemical formula ABX 3 , as illustrated in Figure 1a. Organic-Inorganic hybrid PSCs are typically made using an organic/ inorganic cation (A = methylammonium (MA) CH 3 NH 3 + , formamidinium (FA) CH 3 (NH 2) 2 + , or cesium), a divalent cation (B = Pb 2+ or Sn 2+) , [29] and an anion (X = Cl − , Br − , or I −), illustrated in Figure 1b. [16,30] A is surrounded by eight lead halide octahedra (B in the center of octahedra) and forms a cubic perovskite structure. When the size of A or/and X is changed, the structure of perovskite will distort. The Goldschmidt tolerance factor (t) [31] of perovskite is an empirical index for Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted significant attention in recent years due to their high-power conversion efficiency, simple fabrication, and low material cost. However, due to their high sensitivity to moisture and oxygen, high efficiency PSCs are mainly constructed in an inert environment. This has led to significant concerns associated with the long-term stability and manufacturing costs, which are some of the major limitations for the commercialization of this cutting-edge tech...