Fabrication of SnO2 layer as electron transport layers for perovskite solar cells

Abstract

A SnO2 has attracted more attention as electron transport layer (ETL) for perovskite solar cells (PSCs) because it has diverse advantages, e.g., wide bandgap energy, excellent optical and chemical stability, high transparency, high electron mobility, and easy preparation. In this work, SnO2 layer was fabricated by spin-coating and RF magnetron sputtering techniques with various conditions. The SnO2 layer was integrated into the planar structure of PSCs consisting of FTO/SnO2/MAPbI3/spiro-OMeTAD/Au. For spin-coating, SnO2 films can fully cover the FTO, but it has some particulates from recrystallization of SnO2 precursor as observed in the FESEM images. For RF sputtering technique, morphology of SnO2 films on SLG substrates is very smooth. The optical transmission of the SnO2 films was approximately 85 - 90% in the visible region. It was found that the optimum thickness of SnO2 layer was approximately 35 - 40 nm. The band gap energy (Eg) of SnO2 by sputtering was about 4.2 eV. The sputtered SnO2 based devices were demonstrated to have better device performance and stability than spin-coated SnO2 based devices. Wet chemical processes were avoided to minimize the particulates from recrystallization of SnO2 precursor that led to uneven surface of the ETL layer. It was found that the PSC based on sputtered SnO2, with the sputtering power of 60 W and Ar gas pressure of 1 × 10–3 mbar with O2 gas partial pressure of 1 × 10–4 mbar delivered champion power conversion efficiency (PCE) of about 17.7%.