Electrical Properties of Thin Film Al-(N)Cdse/(P)Si-Al Heterojuction and its Performance as a Photovoltaic Converter

To fabricate the (n)CdSe/(p)Si heterojunctions, Ag-doped CdSe thin films of doping concentration up to 7.23×10^{16cm-3 have been deposited onto p-type silicon wafer by sequential thermal evaporation technique. Different junction parameters such as diode ideality factor (n), built in potential (V_bi), reverse saturation current density (J₀), Richardson's constant (A*), short-circuit current (V_oc), etc. were determined from current-voltage (I-V) characteristics. The ideality factor was found greater than unity with high series resistance (R_s). These parameters show significant changes with variations of doping concentration and temperature. The I-V characteristics under illumination showed poor photovoltaic (PV) effect. However the structures showed the change of PV effect, giving a fill factor (FF) 0.43 for annealed sample with an open-circuit voltage (V_oc) 100 mV, a short-circuit current density (J_sc 13.2 μAcm-2 on increasing the doping concentration up to N_d = 7.23×1016cm-3. Large series resistance, high defect density and presence of interfacial layer are thought to be responsible for higher values of ideality factor and poor PV conversion efficiency. Proper doping and annealing are necessary to reduce the series resistance so as to achieve an ideal and high efficiency PV device.}