Solution-processed thin films of tris(8-hydroxyquinoline)
aluminum (Alq3) have been produced and examined
as an electron transport layer in P3HT:PCBM bulk
heterojunction organic solar cells. UV–Vis absorption,
XRD, SEM and current density–voltage (J–V) measurements
both in dark and under illumination have been carried
out. Absorption spectra of the active layer show
typical P3HT:PCBM absorption features with a maximum
absorption peak around 500 nm and two vibronic shoulders
around 550 and 600 nm which were attributed to the interchain
stacking of P3HT. Furthermore, XRD measurements
revealed that the co-solvent processed film shows better
crystallinity than the mono-solvent film. On the other hand,
SEM images show a clear pinholing effect in the DCBprocessed
film which may cause leakage current that reduces
the fill factor and overall power conversion efficiency
(PCE) of the organic solar cell (OSC). Alq3
absorption spectra show an absorption peak in the UV region,
with an optical band gap of 2.83 eV. The incorporation
of Alq3 films as an electron transport layer in ITO/
PEDOT:PSS/P3HT:PCBM/Alq3/Al structure has resulted
in a significant enhancement in the performance of the
studied OSC devices. The use of mixed solvents of
dichlorobenzene and chlorobenzene (DCB:DB) together
with the inclusion of Alq3 layer has resulted in enhanced
PCE which reached 3.92 %.