Organic photovoltaic devices (OPVs) during the last decade have attracted a significant attention due to their simple processability and their advantages such as low costs and consider as an environmentally friendly and promising source of renewable energy. One of the main challenges faced by researchers in this field is how to improve the performance of the organic solar cells. In this thesis, a scientific approach has been used to optimize organic photovoltaic (OPV) devices and modify the hole transport layer (HTL) and electron transport layer (ETL). All devices in this work were prepared using Poly(3-hexylthiophene-2,5-diyl) (P3HT) as the donor and indene-C70 bisdduct (IC70BA) as the acceptor in the fabrication of the active layer of OPVs. Poly(3, 4 ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was used as the hole transport layer, indium tin oxide (ITO) as anode and then aluminium (Al) was evaporated as the cathode. Optical, electrical, and morphological properties were investigated in all stages of these fabricated organic solar cells using different facilities such as UV visible spectrophotometer, atomic force microscopy (AFM) and current density-voltage (J-V) characterisation.
In the first part of this research, the optimisation of devices was carried out through investigating the use of different solvents, concentrations of active layer components, annealing temperatures, annealing time and the use of a buffer layer. For the solvents, three different solvents were used; chlorobenzene (CB), diochlorobenzene (DCB) and their co-solvent Mix (DCB:CB) and the results indicated that (DCB) showed the best PV behaviour with power conversion efficiency (PCE) of 2.8 %, short circuit current density (Jsc) of 17.04 mA.cm-2, and open circuit voltage (Voc) of 0.33V and fill factor (FF) of 55%. At the end, the final optimum structure was ITO/PEDOT:PSS/P3HT:IC70BA/LiF/Al with significant improvement in PCE of 5.5%, Voc = 0.79 V, FF of 56% and Jsc = 12.5 mA.cm-2.
In the second part aimed to improve OPV performance by modifying the hole transport layer using different metal salts, which are Copper Chloride (CuCl2) and Lithium Chloride (LiCl). Each of salts was dissolved in a certain volume of deionized (DI) water, then mixed with accurate amount of PEDOT:PSS. While using PEDOT:PSS as a typical hole transport layer has shown PCE of 5.5%, the modified (HTL) by LiCl has increased to 18.4 %, with significant improvement in Jsc of 43.12 mA.cm-2, Voc = 0,77 V and FF of 55%.
In the third part, effect of Graphene as (ETL) has been studied. Two different solutions of graphene (normal one and chemically treated one) were used with different thicknesses and different concentrations. The highest results were for treated chemically, which were The PCE of 13.7%, Jsc of 50.08 mA.cm-2, Voc = 0.61V and FF of 55%.