ELECTRICAL PROPERTIES OF P3HT (POLY [3-HEXYLTHIOPHENE])/n-TYPE CRYSTALLINE SILICON (n-c-Si) SOLAR CELLS

Abstract

Au/P3HT (poly [3-hexylthiophene])/n-type crystalline silicon (n-c-Si) solar cells have been fabricated. The Aluminum back contact is obtained by evaporation on silicon substrate. An 80 nm P3HT layer thick was spin-coated on silicon substrate followed by thermal annealing. Finally golden contacts are deposited by sputtering. The best characteristics of this flawed solar cell are: Voc=0.47 V, Isc=7.42 mA/cm 2 and an efficiency of 1.29%. The area of this device is 0.07 cm 2 . In order to get a deep understanding of the electrical properties of the heterojunction, capacitance-voltage and current-voltage-temperature measurements have been made. A compact electrical equivalent circuit has been used to describe the dark current-voltage characteristics. It is based on the combination of two exponential mechanisms, shunt and series resistances and space-charge limited current terms. From the temperature dependence of the extracted parameters we can obtain the limiting conduction mechanism. We found that the polymeric layer limits the current not only at low voltages, through Multi-Tunneling Capture Emission, but also at high voltages, through series resistance and Space-Charge Limited Current. On the other hand, the Silicon wafer limits the current at medium voltages, through the diffusion mechanism. In addition, the model is useful to estimate the open circuit voltage and built in voltage of the solar cell using only dark current voltage measurements.Keywords: P3HT; conduction mechanisms; equivalent circuit.where J D1 and J D2 are density currents of two ideal exponential diodes with their respective reverse saturation currents J S1 , J S2 and exponential factors A 1 , A 2 . R S and R SH are the series and shunt resistance, respectively. The J SCLC is a mechanism of Space Charge Limited Current. Eight circuital model parameters (J S1 , A 1 , J S2 , A 2 , R S , k, m and R SH ) are extracted using a numerical procedure, reported elsewhere [11]. V D , V B and V J are the applied voltage, the voltage drop in the bulk and the voltage drop in the junction, respectively.