Energy\nLevel Tuning in CsPbBr<sub>3</sub> Perovskite\nSolar Cells through In Situ-Polymerized PEDOT Hole Transport Layer

The\nall-inorganic CsPbBr<sub>3</sub> perovskite solar cells exhibit\nexcellent stability against humidity and thermal conditions as well\nas relatively low production cost, rendering them a gradually emerging\nresearch hot spot in the field of photovoltaics. However, the absence\nof a hole transport layer (HTL) in its common structure and the substantial\nenergy level difference of up to 0.6 eV between the highest occupied\nmolecular orbital (HOMO) level of CsPbBr<sub>3</sub> and the work\nfunction of the carbon electrode have emerged as the primary factor\nlimiting the improvement of its power conversion efficiency (PCE).\nIn this work, the monomer 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT)\nis spin-coated onto the surface of the CsPbBr<sub>3</sub> film directly\nand then subjected to annealing; DBEDOT undergoes in situ polymerization\nto form poly(3,4-ethylenedioxythiophene) (PEDOT), which aims to ameliorate\nthe issue of excessive energy level difference between CsPbBr<sub>3</sub> and the carbon electrode, and to facilitate the extraction\nand transport efficiency of holes between the CsPbBr<sub>3</sub> perovskite\nand the carbon electrode. Compared to the pristine device, the PCE\nof the device based on in situ polymerization is enhanced and achieves\na maximum efficiency of 9.81%. Furthermore, the unencapsulated devices\nbased on in situ polymerization maintain 95.9% of their original efficiency\nafter 40 days of stability testing.