Interface engineering of C60/ fluorine doped tin oxide on the photovoltaic performance of perovskite solar cells using the physical vapor deposition technique

Abstract

Fullerene (C60) has been demonstrated, using vapor deposition, to be a good electron transport layer (ETL) and different thicknesses have been utilized in n-i-p configuration perovskite solar cells. However, an underlying reason for the variation in thicknesses, which hinders the reproducibility of perovskite solar cells employing a C60 ETL, has not been well-examined. This study reveals that the surface roughness of the conducting glass, such as fluorine doped tin oxide (FTO), affects the photovoltaic performance while optimizing the thickness of the vacuum deposited compact C60 ETL. A low-thickness C60 ETL retains a surface roughness and Ohmic behavior similar to bare FTO due to physical defects at the C60/FTO interface. Increasing the thickness further reduces the defects at the C60/FTO interface and facilitates an enhanced electron extraction from a vacuum co-deposited methyl-ammonium lead iodide perovskite light absorber. As a result, a perovskite solar cell with a homogenously covered C60 ETL on an FTO substrate delivers a power conversion efficiency of 14.63%. These comprehensive characterizations support the finding that suppression of defects at the C60/FTO interface results in an improved photovoltaic performance. This work demonstrates that the surface roughness of FTO needs to be considered for a decisive compact ETL for enhanced photovoltaic performance and reproducibility.