Environmental Engineering Reference
In-Depth Information
Fig. 5 a J-V characteristics
of typical MDMO-PPV/
PCBM solar cells
incorporating LiF/Al
electrodes of various LiF
thicknesses, compared with
the performance of the device
featuring a pristine Al
electrode. b, c Box plots of
the FFs and values of Voc
obtained from six separate
solar cells [ 23 ]
electrons efficiently. Figure 5 displays a classic example of the function of an
interlayer: here, both the open-circuit voltage (V oc ) and fill factor (FF) of the OPV
improved, yielding increased PCEs after the insertion of a layer of LiF [ 23 ]. This
photoactive layer comprised PCBM and poly[2-methoxy,5-(3 0 /7 0 -dimethyloctyl-
oxy)]-p-phenylenevinylene (MDMO-PPV); the FF increased by up to approxi-
mately 20 % relative to that of the reference cell featuring a pristine Al electrode.
Together with a short-circuit current of 5.25 mA cm -2 and a value of V oc of
0.825 V, the PCE reached 3.3 % under illumination with white light. The authors
suggested that the formation of a dipole moment across the interface was the main
mechanism behind the improved device performance [ 23 ].
The preparation of most of the above-mentioned interlayers required an addi-
tional step, the deposition of the thin film, thereby complicating the device fab-
rication process and possibly increasing the cost. More recently, our group
conceptually demonstrated a novel method for interface modification toward
preparing self-organized bilayer structures in OPVs [ 28 , 29 ]. In this approach, only
a single step is required to fabricate both the active and buffer layers, thereby
simplifying the fabrication process. The buffer layer material we employed,
poly(ethylene glycol) (PEG), is an insulating polymer. After chemical interaction
with Al atoms, the PEG molecules formed an effective cathode contact with the
photoactive layer. Figure 6 a outlines the procedure used for the fabrication of an
OPV featuring such a self-organized bilayer (P3HT:PCBM/PEG) structure. The
PEG molecules were directly blended with P3HT and PCBM; the device was
fabricated using a conventional spin-coating process. During the drying process,
Search WWH ::




Custom Search