Application of a hole transporting organic interlayer in graphene oxide/single walled carbon nanotube–silicon heterojunction solar cells

The solid-state hole transporting material 2,2′,7,7′-tetrakis(N,N′-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) has been applied as an interlayer for graphene oxide/single walled carbon nanotube-silicon (GOCNT/Si) heterojunction solar cells, forming a GOCNT/spiro-OMeTAD/Si structure. An organic-aqueous transfer method was developed to deposit the GOCNT electrode onto the spiro-OMeTAD coated Si surface without dissolving the organic layer. The influence of the thickness of the organic layer and the thin film GOCNT transparent conducting electrodes as well as the doping of the films with gold chloride (AuCl₃) on device performance is explored. With the optimized thickness of the spiro-OMeTAD interlayer and the GOCNT electrode with transmittance above 80% at 550 nm, devices with solar power conversion efficiency of 12.83 ± 0.22% have been fabricated. This study reveals that adding a hole-conducting organic interlayer is able to significantly minimize the recombination at the heterojunction interface. In addition to improving performance, the spiro-OMeTAD behaves as a physical protection layer to significantly enhance device stability.