Influences of electron transport layer thickness on functional characteristics of Formamidinium lead iodide featured with silver back contact solar cell

Abstract This study investigates how different thicknesses of the electron transport layer (ETL) impact the performance of Formamidinium lead iodide (FAPbI 3 ) solar cells with a silver back contact. The solar cell structure includes a 200 nm-thick fluorine-doped tin oxide (FTO) window layer, a Formamidinium lead iodide layer for light absorption, and a tin(IV) oxide (SnO 2 ) layer serving as the ETL, with thicknesses of 5, 10, 15, and 20 nm. Using the spin-coating method with anti-solvent treatment, followed by annealing at 400 °C, solar cells were fabricated with and without the SnO 2 -perovskite absorber. Results show that the ETL thickness significantly affects key performance parameters, including charge transport, recombination, and overall efficiency. The perovskite solar cells featuring with 20 nm SnO 2 layer have a crystallite size of 40.1 nm. It also shows the lowest transmittance at 45 % and the highest absorption coefficient at 7.5 × 10 4 per cm. This material also has the highest refractive index of 2.2, the best conductivity of 0.55 × 10 −2 S/cm, and the lowest resistivity at 1.82 × 10 2 Ω cm. Moreover, the optical band gap decreases to 1.52 eV, resulting in a higher short-circuit current density (Jsc) of 23.5 mA/cm 2 and an open-circuit voltage (Voc) of 1.2 V. An optimum performance of perovskite solar cells featuring 20 nm SnO 2 is recommended for solar cell applications.