IMPROVED PHOTOVOLTAIC PROPERTIES FOR AU ALPCCL/N-SI SOLAR-CELLS WITH MORPHOLOGY-CONTROLLED ALPCCL DEPOSITION/

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.