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The role of multilayer graphene in the improved electrical and optical characteristics of a P3HT-based photovoltaic device

In the present work, we have studied in detail the effect of the incorporation of multilayer graphene (MLG) on the electrical and optical properties of P3HT (poly (3-hexylthiophene))-based photovoltaic (PV) devices. The PV devices were fabricated with a P3HT:MLG composite and significant improvement in the performance was observed in terms of enhanced short circuit current density (Jsc) and open circuit voltage (Voc) at the optimized MLG concentration of 0.1 wt%. The dark I–V measurements exhibit a remarkable reduction in the total series resistance (Rs) of about 63% in our typical device which is attributed to the increase in the mobility of charge carriers in the P3HT:MLG (0.1 wt%) composite film. A prominent quenching in the photoluminescence (PL) of P3HT on the addition of MLG indicates efficient electron extraction from P3HT and therefore, the increase in the Jsc is the combined effect of both the efficient charge transfer and reduction in the Rs of the device. Further, cyclic voltammetry (CV) measurements reveal that on adding MLG, there is a downshift of the highest occupied molecular orbital energy level of P3HT which in turn increases the Voc of the device by ~0.28 V.