A Simple Approach for the Fabrication of Perovskite Solar Cells in Air

Data collection method:

The methodology is given in full in the paper: http://opus.bath.ac.uk/46898/ The FTO/glass substrate (TEC 7, 8 Ohm □-1, 25 x 25 mm) was etched into the desired pattern with Zinc powder and 2 M HCl diluted in deionized water. The substrates were first cleaned with Hellmanex (2% solution) diluted in deionizer water, then with isopropanol, and finally acetone. They were then treated with an oxygen plasma for 15 min to remove any remaining organic residues. Logical steps to fabricate the devices are shown in Figure S10, ESI. A TiO2 blocking layer (bl-TiO2), made according to a reported procedure, [31] was deposited onto the substrate by spin-coating at 2000 RPM for 60s and after drying at 150 °C for 15min a sintering process at 500 °C for 30min was done. To obtain a mesoporous layer, a TiO2 paste (Dyesol 18NR-T) was diluted 1:5 with ethanol and spin coated on the substrate at 1000 RPM for 60s (thickness around 300 nm). The samples were dried in an oven at 100 °C for 10 min and then sintered at 500 °C for 30 min. PbI2 powder (Aldrich, 99%) was dissolved either in DMF or in DMSO solvent (at a concentration of 400 mg ml-1) and stirred at 70 °C. The hot PbI2 solution was spin-coated on either a mesoporous scaffold to obtain mesoporous structure, or directly on the bl-TiO2, to obtain a planar structure, at 4000 RPM for 30s on substrates preheated to 70 °C. These were then dried at 120 °C for 1h in air to remove the solvent and drive the crystallization. For the perovskite growth, the sample was put on a hot plate and surrounded by MAI powder. The samples and the powder were put under low vacuum (desiccator lid attached to an Edwards 5 E2M5 Rotary Vane Dual Stage Mechanical Vacuum Pump) and heated at 150 °C for the desired time. For the hole transport material (HTM), 142.6 mg of Spiro-OMETAD was dissolved in 2 ml chlorobenzene (Aldrich, anhydrous 99.8%) and 4-tert Butylpyridine (17.5 µl, 96%, Aldrich) were added as well as previously prepared bis(trifluoromethane)sulfonimide lithium salt solution (37.5 μl of a 170 mg ml-1 LiTFSI, Aldrich, solution in acetonitrile). The HTM was spin coated at 4000 RPM for 45s and then left in air overnight in a closed box containing silica desiccant. Finally the samples were introduced into a high vacuum chamber to evaporate gold (Au) back contacts (thickness 80 nm). Each substrate has 10 pixels with 0.1 cm2 of active area. Powder X-ray diffraction (XRD) analysis was performed to investigate the phases of the samples, using a BRUKER D8-Advance. For the Atomic Force Microscope AFM measurements a Nanosurf AG, Easyscan 2 was used operating in dynamic force mode. Device performance was evaluated using a Class AAA solar simulator at AM 1.5G and 100 mW cm-2 connected to a source-meter (Keithley 2601A). For the measurements, the samples were covered with a shadow mask with an opening area of 0.1 cm2 to illuminate only one cell at a time. Before measuring the reverse JV curve the sample was maintained for 5 seconds stabilization time at 1.2V forward bias under illumination. A custom-made tool comprising a sourcemeter (Keithley 2612) and a monochromator (Newport 74000) was used to measure the external quantum efficiency (EQE) values of the device. For chronoamperometry measurements the cells were illuminated with a white LED (100 mW cm-2, 3 Watts- 4200K luxeon star).

Data processing and preparation activities:

Full details of the data processing are given in the paper