6.56% Efficient CuInS ₂ Superstrate Solar Cells Enabled by an Amorphous Tin Oxide Interlayer

Herein, for the first time, we have fabricated superstrate-type CuInS2 planar heterojunction solar cells configured as FTO/SnOx/CdS/CuInS2/Spiro-OMeTAD/Au, in which an amorphous tin oxide (SnOx) interfacial layer is prepared by a straightforward solution-processing method at low temperatures (≤200 °C), and 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD) is used as a hole-transporting material. It is revealed that the solar cells exhibit a performance that is strongly dependent on the SnOx layer thickness and deliver a peak power conversion efficiency of 6.56% for a 25 nm-thick SnOx layer, which is higher by 78% than that of the control devices without the SnOx interfacial layer. This is attributed to the reduced interfacial charge recombination at the CdS/CuInS2 interfaces due to the fast extraction of photogenerated electrons from the CdS layer into the SnOx film for collection. This work offers promising interfacial access to efficient CuInS2 planar heterojunction solar cells.