posted on 2021-09-03, 11:33authored byMin-Ah Park, Sae Jin Sung, You Jin Ahn, Inhwa Hong, Ik Jae Park, Chong Rae Park, Jin Young Kim
A thin graphene oxide (GO) layer
has been prepared on indium tin
oxide (ITO)-coated glass and plastic (polyethylene naphthalate; PEN)
substrates for the application as a hole transport layer (HTL) of
p–i–n-type planar perovskite solar cells. Transparent
devices can be fabricated by replacing the Ag top electrode of conventional
nontransparent devices with an ITO top electrode using radio frequency
(RF) sputtering. The GO layer with high transmittance in the visible
range exhibits excellent hole-extracting capabilities from the perovskite
layer. Scanning electron microscopy (SEM) and atomic force microscopy
(AFM) analyses reveal that the GO HTL uniformly covers the substrate.
In addition, the GO-based devices show significantly improved long-term
stability compared with the conventional poly(3,4-ethylenedioxythiophene)
polystyrene sulfonate (PEDOT:PSS)-based counterparts. The enhancement
in stability becomes much more apparent for flexible devices with
the PEN substrate, which has been attributed to the excellent barrier
properties of the GO HTL. As a result, a transparent and flexible
p-i-n-type perovskite solar cell with a bifunctional GO HTL exhibits
a high efficiency of 9.34% (cf. 11.39% for the glass substrate and
12.31% for the nontransparent/glass substrate) and good long-term
stability.