  Photovoltaic (PV) devices made from blends of a polyarylamine biscarbonate
ester (PABC) and [6,6]-phenyl $C_{61}$ butyric acid methyl ester (PCBM) have
been fabricated and characterized. PABC is a hole transporting co-polymer
prepared from reacting
N,N'diphenyl-N,N'bis(3-hydroxyphenyl)1,1;biphenyl(4,4'diamine), diethylene
glycol bischloroformate, and triethylemine. By varying the polymer loading in
the blend, optimal power conversion efficiency (PCE) of approximately 0.45\%
has been achieved for a blend consisting of 25 wt\% PABC, which is an order of
magnitude higher than the PCE for a 45 wt\% blend. The optimal ratio is at
about 0.44:0.56 molar ratio of the active hole transporting to electron
transporting moieties. Results of mobility studies suggest that blends with
higher PABC loading have efficiencies limited by 'hole' transport. Also
responsible for the lower efficiency at higher PABC concentrations was optical
filtering. The efficiency does not appear to be limited by deep charge
trapping. Density functional theory calculations conducted pointed toward a
strong localization of the frontier orbitals, which might offer an explanation
for the low PABC hole mobility. Calculated frontier orbital energy levels found
band gap to be consistent with the $V_{OC}$ measured.
