| Several aspects of organic photoconductors investigated for photovoltaic (PV) applications are addressed: material selection criteria, device modelling, and the characterization techniques of I-V, capacitance-voltage (C-V), {dollar}Isb{lcub}sc{rcub}{dollar} vs. {dollar}Vsb{lcub}oc{rcub}{dollar}, and internal photoemission. Experimental results are presented for chloroaluminum phthalocyanine (ClAlPc) Schottky barrier and p-n heterojunction cells.; The principal limitation of organic PV materials is a low field-dependent photocarrier generation efficiency. P-n heterojunction cells have advantages over Schottky cells, having better spectral coverage and the ability to utilize Forster transfer for the transport and concentration of excitons to a high field region. A promising approach pairs a phthalocyanine and a perylene. A simpler Schottky barrier system is modelled using parameters for the field-dependent generation of metal-free phthalocyanine. The effects of doping level, {dollar}alpha{dollar}, and other parameters on the external cell characteristics are calculated based on the electric field in the depletion region. Although this modelling does not include the effects of exciton diffusion, the wavelength dependence of the external quantum efficiency mimics results thought to indicate an exciton diffusion process.; The device fabrication procedure utilizes vacuum deposition of organic semiconductors purified by entrainment sublimation. Films deposited at different substrate temperatures are characterized with optical absorption, x-ray, and scanning electron microscopy. A hydration mechanism for ClAlPc is uncovered, and powder x-ray results are presented.; The photoresponses for a perylene derivative paired with ClAlPc and PcAlOAlPc are presented. The C-V spectroscopy methods are reviewed, and the small signal method is argued to be preferable to the triangle voltage sweep method due to the likely presence of deep traps and interface states. C-V results are shown to bias hold-time dependent so that straight 1/{dollar}Csp2{dollar} vs. V plots should be interpreted with caution. Experiments under vacuum, air, dry oxygen, water vapor, and oxygen with water vapor ambients show water and oxygen are necessary for the ClAlPc to exhibit significant conductivity and C-V response. This suggests that water and oxygen must both be present for significant doping effects. |
