Stabilization of Intrinsic Ions in Perovskite Solar Cells by Employment of a Bipolar Star-Shaped Organic Molecule as a Charge Transport Buffer

The stability of perovskite thin films is one of the most critical challenges for their practical application in photovoltaic devices. The defects of hybrid organic-inorganic perovskites, such as the photogenerated Pb-0 and iodine (I-0), will cause lattice distortion and act as recombination centers, which will also make the photovoltaic behavior worse. Introducing properly designed additives might minimize this harmful mechanism. The designed molecule core calix[4]resorcinarene (CRA)-triphenylamine (TPA) that contains hole transport functional groups (TPA) and electron transport functional groups (triazole) has been synthesized and employed as an additive in the perovskite, where it serves as an adjust buffer of charge transport. We found that this novel molecule improves the crystallization of triplecation perovskite films. The power conversion efficiency of 18.5% of the control device is increased to 20.0% by introducing a proper amount of CRA-TPA. The defect density of the perovskite layer has been substantially decreased to approximate to 1/4 with the introduction of the designed additives, with stability benefiting as well.