Thin Film Perovskite Solar Cells: Fabrication via Spin Coating, Flash Evaporation and Chemical Vapor Deposition (CVD)

Abstract

In this work, thin film perovskite solar cells with different compositions have been manufactured with the help of the methods: spin coating, spray pyrolysis, etching, sputtering, chemical bath deposition, flash evaporation and chemical vapor deposition (CVD). The solar cells and their materials have been characterized electrically at the solar simulator setup, respectively through UV/Vis absorption spectroscopy, photoluminescence (PL), scanning electron microsco-py (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). In a classical approach, which has been optimized within our Surface Science group, a two-step spin coating and chemical bath deposition method for producing the perovskite material methylammonium lead iodide (MAPI) was used in this work to manufacture Glass/FTO/c-TiO2/m-TiO2/MAPI/spiro-MeOTAD/Au solar cells, having a maximum power conversion efficiency (PCE) of 15,6 %, with a solar cell dimension of 32,5 mm2 and a mini-module substrate dimension of 4 cm2. In a next approach, a one-step spin coating and antisolvent method was used according to literature1 to deposit a thin film of a triple cation, double anion lead perovskite: (CsaMAbFAc)1PbIxBr3-x. This approach is used to compare the performance of solar cells made using our lab methods and the production of our own stack of materials Glass/FTO/c-TiO2/m-TiO2/(CsaMAbFAc)1PbIxBr3-x/spiro-MeOTAD/Au with those in literature. While according to literature1 the published per-ovskite recipe reached a maximum PCE of over 20% in the authors’ labs, a maximum efficiency of 18,5 % could be obtained within this work. A further increase in efficiency is discussed with respect to our solar simulator measurement method. Furthermore, a flash evaporation setup has been built and employed in a novel solvent-free approach to produce films of the alterna-tive perovskite material for solar cells, methylammonium tin iodide (MASI), which uses tin (Sn) instead of the widely used lead (Pb). These experiments show that the flash evaporation pro-cess can produce MASI films of a high chemical purity. Additionally, a new chemical vapor deposition (CVD) setup has been built and used to test a variety of precursor combinations for synthesizing methylammonium lead iodide (MAPI), formamidinium lead iodide (FAPI), or hy-drogen lead iodide (HPbI3). For producing MAPI perovskite films, methylamine gas (MA) and home-made hydrogen iodide (HI) gas were successfully used. For these reactions, the mecha-nism has been clarified using XPS and XRD. The best solar cell built using the up-scalable CVD setup shows an efficiency of 12,9 %.