Effect of thickness on the performance of hybrid solar cells fabricated using surfactant free lead sulfide quantum dots and poly(3-hexylthiophene-2,5-diyl) polymer

Surfactant free lead sulfide (PbS) nanoparticles (NPs) had been synthesized by precipitation method using lead acetate and thiourea as precursor. Mechanical grinding using mortar pestle has been done to deagglomerate the NPs to obtain finer nanoparticles. Ground NPs were further sonicated using high power probe sonicator in chlorobenzene solution. The poly(3-hexylthiophene-2,5-diyl) (P3HT) polymer was added into the chlorobenzene solution containing well dispersed PbS quantum dots (QDs). The blends solution containing PbS QDs and P3HT polymer was spin coated at different rotation per minute to obtain an optimum thickness for efficient hybrid solar cells fabrication. Scanning electron microscopy, atomic force microscopy and transmission electron microscopy analysis showed a homogeneous distribution of PbS QDs in the P3HT matrix. Photoluminescence (PL) measurements performed on the blends solution showed strong PL quenching, which was very much dependent on the PbS QDs concentration, indicating that proper photoinduced electron and hole transfer occurred in PbS:P3HT blend. Hybrid solar cells with configuration indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)/PbS:P3HT/Al had been fabricated with different active layer thicknesses. The device with optimum thickness showed the highest efficiency of 1.75% under Air Mass 1.5G illumination with the irradiation of 100 mW/cm2. Morphological and optical investigations showed that improvement in the performance was achieved for the optimum thickness of the active layer due to good distribution and interconnection of surfactant free PbS QDs in P3HT matrix.