H. Yanagi et al., IMPROVED PHOTOVOLTAIC PROPERTIES FOR AU ALPCCL/N-SI SOLAR-CELLS WITH MORPHOLOGY-CONTROLLED ALPCCL DEPOSITION/, Journal of applied physics, 75(1), 1994, pp. 568-576
Photovoltaic solar cells were constructed by successive vacuum deposit
ion of chloroaluminum phthalocyanine (AlPcCl) and Au on a single-cryst
al n-Si wafer. By controlling the thickness and morphology of the AlPc
Cl deposits in the Au/AlPcCl/n-Si cells, an improved photovoltaic effi
ciency was obtained as compared to the Au/n-Si Schottky-type cell. The
cell with a homogeneous, ultrathin (10 nm thickness) AlPcCl film, whi
ch was prepared by deposition on an n-Si substrate kept at -20 degrees
C, exhibited a high photovoltage (V-oc=0.45 V) and strongly sensitize
d photocurrents in the e-band absorption region (600-800 nm) of AlPcCl
chromophore. This improved photoresponse was attributed to a space-ch
arge layer generated inside the AlPcCl film, where the intervening AlP
cCl layer prevented the n-Si surface from forming surface states becau
se of noncontact with the Au top electrode. When discontinuous island
crystallites of AlPcCl were formed on the n-Si surface kept at 200 deg
rees C, the Au/AlPcCl/ n-Si cell also exhibited an improved efficiency
with a high photovoltage (V-oc=0.42 V). The discontinuous AlPcCl cove
rage, providing both the Au/n-Si Schottky contact and AlPcCl/n-Si hete
rojunction, modulated a diffusion potential at the space-charge region
to give rise to a steep barrier gradient at the edges of the AlPcCl i
sland. Its high photovoltaic response was attributed to an efficient c
harge-carrier separation from excitons that were generated on the unco
ated n-Si area and diffused at the AlPcCl-island edge.