Transport mechanisms and photovoltaic properties of zinc tetraphenylporphyrin/n-type silicon heterojunction solar cell

Abstract

The DC electrical measurements on Au/ZnTPP/Au planar structure showed two regimes of electrical conductivity depending on temperature, at low temperatures the activation energy is 0.24 eV and variable range hopping in localized states near Fermi level is the operating conduction mechanism, at high temperatures the activation energy is 0.998 eV and phonon-assisted hopping of small polarons is the operating conduction mechanism. The capacitance-voltage measurements on Au/ZnTPP/n-Si/Al showed that the formed junction is linearly graded one. The thickness of depletion region in ZnTPP and n-Si has been determined and the built-in potential is 0.85 V. The concentration gradient of holes and electrons is 2.6 × 1020 holes/m4 and 0.3 × 1020 electrons/m4, respectively. Thermoelectric power measurements showed that ZnTPP films are p-type semiconductor and polaron activation energy is 0.37 eV. A hybrid solar cell of Au/ZnTPP/n-Si/Al had been constructed by growing ZnTPP film via thermal evaporation technique on n-Si wafer. Dark current-voltage measurements of the device at different temperatures showed that there are three conduction mechanisms operating in the device. The dominance of any of them depends on applied potential. The photovoltaic properties of Au/ZnTPP/n-Si/Al hybrid solar had been evaluated.