ABSTRACT
Perovskite material CH3NH3PbI3 has also been demonstrated to be capable to transport charge carriers in meso-super-structured and thin-film planar structure device configuration, triggering researchers to investigate on its hole-transporting properties concurrently and resulting in other types of perovskite solar cell (PSC) structures without hole-transporting layer. Thus, besides the typical p-i-n structure PSCs with organic or inorganic hole-transporting materials (HTM) which have achieved high efficiencies, there have also been attempts to construct perovskite-based solar cells completely free of HTMs. Polymer-wrapped single-walled carbon nanotubes (CNT) are mixed with pristine spiro-OMeTAD to act as the double-layer structure of hole-transporting p-type layer. Other attempts to construct HTM-free PSCs to lower down the cost include replacing the gold contact with carbon-based material, such as graphite and CNTs. The chapter shows that various research works from worldwide research groups on the elimination of organic or inorganic hole-transporting layer in PSC.
