posted on 2023-12-04, 13:36authored byJunyi Xu, Junsheng Luo, Kirill Gubanov, Anastasiia Barabash, Rainer H. Fink, Thomas Heumüller, Christoph J. Brabec
Realizing
efficient and stable organic solar cells (OSCs)
via all-solution
processing requires the design of tailored charge extraction interfaces.
Herein, we demonstrate a substantially different interface concept
for OSC that is based on a low-temperature processed mesoscopic hole
transporting layer (HTL) derived from partially covered organic nanoparticles
(NPs) in the n-i-p structure. The mesoscopic interface is further
doped in a second coating step with an organic salt dopant, BCF-Li.
The interactions among the dopant, the solvent for sequential doping,
and the semiconductor layer are surprisingly complex. The mesoscopic
interface is necessary to evenly wet the semiconductor and prevent
the aggregation of the dopant. At the same time, the sequential process
reduces the excess acceptor at the interface. Both processes together
are necessary to generate an efficiently doped interface for low-Ohmic-charge
extraction and stable contacts. Devices with fully solution-processed
mesoscopic interfaces show a superb shelf lifetime of over 22000 h
without encapsulation and a long-term operational stability under
1 sun illumination for 2000 h (T80). Flexible devices bypass 1000
bending cycles with negligible degradation. Mesoscopic doped interfaces
are demonstrated as an alternative to PEDOT:PSS as well as PEDOT related
interface concepts for nonfullerene acceptors (NFA) in the n-i-p architecture.