Introducing Perovskite Solar Cells to Undergraduates.

I this Viewpoint, we show that it is sufficiently easy and cheap to fabricate a perovskite solar cell that this can be done as an undergraduate laboratory experiment. Solar cells, which have been around since the 1950s, are considered as a prominent source of renewable energy in the future. Conventional solar cells, which are used in rooftop applications, are based on single-crystal silicon and are up to 25% efficient. Considerably more expensive solar cells based on GaAs (gallium arsenide) single crystals are ∼29 and over 40% efficient in singleand multijunction devices, respectively. They are used on satellites and in other space applications. Over the past 2 decades, solar cells based on thin-film polycrystalline materials, especially CdTe (cadmium telluride) and CIGS (copper indium gallium selenide), have emerged as a viable alternative to silicon cells with efficiencies exceeding 20%. A new arrival in this family is organic−inorganic halide perovskites. First introduced in 2012, the efficiency of these cells has risen from 10 to 20% in just 2 years. This is to be compared to the mainstream of emerging photovoltaic technologies, such as polymer cells, dye-sensitized solar cells (DSSCs), and quantum dot solar cells, which are 8− 13% efficient after 2 decades of research. The sudden emergence of perovskite solar cells and their facile solution-based fabrication method offer a unique opportunity to give chemistry students hands-on experience in mainstream photovoltaics. Currently, only a few solar cell fabrication experiments, primarily DSSCs, are accessible to chemistry students. The laboratory experiment described here leads to fabrication of methylammonium lead triiodide (MAPbI3) perovskite solar cells using a simple step-by-step deposition procedure, followed by measurements with routine equipment. The cost of fabricating one cell is below 20 cents, and it takes 2−5 h. The experiment is suitable for chemistry students to learn about thin-film polycrystalline solar cells, energy conversion, materials and methods, chemical reactivity, stoichiometry, and the optical and electronic properties of materials. A YouTube video of the experiment, which is highly appropriate for a classroom demonstration, is available at: https://www.youtube.com/watch?v=RqW9HrasNPA. Procedure. The solar cell device consists of layers of titania (TiO2), perovskite (CH3NH3PbI3), copper thiocyanate (CuSCN), and carbon particles, sandwiched between two glass plates. A physical model of the device is shown in Figure 1, which is useful to teach solar cell fabrication in classrooms. The fabrication steps are depicted in Figure 2 with detailed description provided below. Step 1. Take a piece of FTO glass (2 cm × 1.4 cm), which is a piece of glass coated with transparent and conductive material, fluorine-doped tin oxide (FTO), on one side. Determine the conducting side using a multimeter. To do this, set the multimeter to resistance mode (200 Ω), plug the two leads into the multimeter, and measure the sheet resistance on the two sides using the probes (Figure 3). The conducting side will give low resistance (tens of ohms), while the uncoated side will not give any value. Notice that the FTO side has more friction compared to the uncoated one when moving the probe over it. Step 2. Place the FTO glass plate on the benchtop with the conductive side facing up. Tape the glass plate to the benchtop with scotch tape covering 1/4 of the surface, as shown in Figure 4. Put one drop of TiO2 precursor solution 17 (0.2 M titanium isopropoxide + 0.1 M HCl in anhydrous ethanol) and spread it across the surface with a pipet. Roll it over the surface several