Organic solar cells with graphene electrodes and vapor printed poly(3,4-ethylenedioxythiophene) as the hole transporting layers

Publication Type:

Journal Article

Source:

ACS Nano, ACS Publications, Volume 6, Issue 7, p.6370-6377 (2012)

ISBN:

1936-0851

Keywords:

2012, 2013 and earlier

Abstract:

For the successful integration of graphene as a transparent conducting electrode in organic solar cells, proper energy level alignment at the
interface between the graphene and the adjacent organic layer is critical.
The role of a hole transporting layer (HTL) thus becomes more significant
due to the generally lower work function of graphene compared to ITO. A
commonly used HTL material with ITO anodes is
poly(3,4-ethylenedioxythiophene) (PEDOT) with poly(styrenesulfonate) (PSS)
as the solid-state dopant. However, graphene's hydrophobic surface renders
uniform coverage of PEDOT:PSS (aqueous solution) by spin-casting very
challenging. Here, we introduce a novel, yet simple, vapor printing method
for creating patterned HTL PEDOT layers directly onto the graphene
surface. Vapor printing represents the implementation of shadow masking in
combination with oxidative chemical vapor deposition (oCVD). The oCVD
method was developed for the formation of blanket (i.e., unpatterened)
layers of pure PEDOT (i.e., no PSS) with systematically variable work
function. In the unmasked regions, vapor printing produces complete,
uniform, smooth layers of pure PEDOT over graphene. Graphene electrodes
were synthesized under low-pressure chemical vapor deposition (LPCVD)
using a copper catalyst. The use of another electron donor material,
tetraphenyldibenzoperiflanthene, instead of copper phthalocyanine in the
organic solar cells also improves the power conversion efficiency. With
the vapor printed HTL, the devices using graphene electrodes yield
comparable performances to the ITO reference devices (η(p,LPCVD) = 3.01%,
and η(p,ITO) = 3.20%).

Notes:

PMID: 22724887