Page 157 - Multifunctional Photocatalytic Materials for Energy

Graphene-based nanomaterials for solar cells 143

for DSSCs with an efficiency of 6.75% [127]. The high efficiency was attributed to the
uniform distribution of catalytic Fe particles on the surface of the HRG. Recently, gold
metal-incorporated, graphene-based composites on FTO substrate used as counter
electrodes in DSSCs have achieved a record efficiency of 14.3%.

7.4.6 Graphene in perovskite solar cells (PSC)

Perovskite solar cells emerged as a new family of solar cells during the past decade.
They are third-generation solar cell and are attractive candidates for future commer-
cialization because of their low-cost, ability to scale up, and high power conversion ef-
ficiency (more than 20%). Similar to DSSCs, PSCs consist of semiconducting TiO 2 as
an electron-transport layer, perovskites as light harvesting materials, a hole transport
layer, and an electrode. Various perovskites, for example, CH 3 NH 3 PbI 3 , CH 3 NH 3 PbB 3 ,
and NCs, are being used in place of dyes in DSSCs [128]. In PSCs, graphene-based
materials are commonly applied as an electron transport layer or a hole transport layer
Fig. 7.3 illustrates the arrangement of perovskite solar cells.
Recently, HRG-TiO 2 nanocomposites were used as an electron transport layer in
2
PSCs and exhibited a maximum PCE of 15.6% with a JSC of 21.9 mA/cm . Also,
graphene quantum dots were introduced between the perovskite and TiO 2 to enhance
the performance of the PSC. In this case, a PCE of 10.15% was achieved, which is
higher than in a PSC without a GQD layer [129]. In addition, binary or ternary oxides
such as SrTiO 3 are considered as suitable alternatives to TiO 2 as ETLs [130]. These
materials decreased charge recombination centers and therefore improved the PCE to
10%. Wu et al. reported inverted planar heterojunction perovskite-based solar cells
using GRO as a hole conductor and CH 3 NH 3 PbI 3−x Cl x as a light absorber [70]. The
deliberately designed device exhibited a high efficiency of 12.4%. In another study,
ultrathin HRG was used as the hole transport material with CH 3 NH 3 PbI 3 as a light ab-
sorber. The PCE of rGO-based PSC was 10.80% and also showed better stability than
a PEDOT:PSS device (maximum PCE, 9.14%) [131].

Perovskite solar cell

Graphene
Counter electrode
Graphene-based material
Hole transport layer Graphene-based nanocomposite
Perovskite layer

TiO 2
FTO glass Graphene-based material

Fig. 7.3 Graphene-based material used in perovskite solar cells.