Improved photovoltaic properties for Au/AlPcCl/n-Si solar cells with morphology-controlled AlPcCl deposition

Abstract

Photovoltaic solar cells were constructed by successive vacuum deposition of chloroaluminum phthalocyanine (AlPcCl) and Au on a single-crystal n-Si wafer. By controlling the thickness and morphology of the AlPcCl deposits in the Au/AlPcCl/n-Si cells, an improved photovoltaic efficiency was obtained as compared to the Au/n-Si Schottky-type cell. The cell with a homogeneous, ultrathin (10 nm thickness) AlPcCl film, which was prepared by deposition on an n-Si substrate kept at −20 °C, exhibited a high photovoltage (Voc=0.45 V) and strongly sensitized photocurrents in the Q-band absorption region (600–800 nm) of AlPcCl chromophore. This improved photoresponse was attributed to a space-charge layer generated inside the AlPcCl film, where the intervening AlPcCl layer prevented the n-Si surface from forming surface states because of noncontact with the Au top electrode. When discontinuous island crystallites of AlPcCl were formed on the n-Si surface kept at 200 °C, the Au/AlPcCl/n-Si cell also exhibited an improved efficiency with a high photovoltage (Voc=0.42 V). The discontinuous AlPcCl coverage, providing both the Au/n-Si Schottky contact and AlPcCl/n-Si heterojunction, modulated a diffusion potential at the space-charge region to give rise to a steep barrier gradient at the edges of the AlPcCl island. Its high photovoltaic response was attributed to an efficient charge-carrier separation from excitons that were generated on the uncoated n-Si area and diffused at the AlPcCl-island edge.