In organic photovoltaic
(OPV) cells, besides the organic active layer, the electron-transporting
layer (ETL) has a primordial role in transporting electrons and blocking
holes. In planar heterojunction-OPVs (PHJ-OPVs), the ETL is called
the exciton blocking layer (EBL). The optimum thickness of the EBL
is 9 nm. However, in the case of inverted OPVs, such thickness is
too high to permit efficient electron collection, due to the fact
that there is no possibility of metal diffusion in the EBL during
the top metal electrode deposition. In the present work, we show that
the introduction of a thin potassium layer between the indium tin
oxide (ITO) cathode and the EBL increases dramatically the conductivity
of the EBL. We demonstrate that K not only behaves as a simple ultrathin
layer allowing for the discrimination of the charge carriers at the
cathode/organic material interface but also by diffusing into the
EBL, it increases its conductivity by 3 orders of magnitude, which
allows us to improve the shape of the
J
–
V
characteristics and the PHJ-inverted OPV efficiency by
more than 33%. Moreover, we also show that PHJ-inverted OPVs with
K in their EBLs are more stable than those with Alq
3
alone.