In this seminar, we will explore the techniques used to tune the energy band gap (Eg) of semiconductors nanoparticles (NPs) for solar cells applications. Two Different types of semiconductors NPs will be discussed: binary semiconductors quantum dots (QDs) as PbS, Ag2S and ternary alloyed semiconductors as Cd1-xPbxS and Pb1-xZnxS (x: 0, 0.1, 0.2, 0.3 and 0.4) QDs. For the first type (binary QDs), tuning the energy band gap is achieved by controlling QDs size. While for the second type (ternary alloyed QDs), tuning the energy band gap is achieved by alloying process. Then, these QDs are adsorbed onto TiO2 (titania) nanoporous films using a sub-sequential chemical deposition technique called successive ionic layer adsorption and reaction (SILAR) method. Moreover, the morphology of the prepared QDs is studied using a scanning and transmission electron microscope (SEM and TEM). The structural properties of the prepared QDs are measured using an X-ray diffractometer and an energy dispersive X-ray (EDX) technique. The optical properties are recorded using a UV-visible spectrophotometer. The optical bowing constant (b) of the alloyed QDs is deduced. The photovoltaic characteristics (short circuit current density Jsc, open circuit voltage Voc, fill factor FF and energy conversion efficiency η) of the assembled QDs sensitized solar cells (QDSSCs) are measured under AM1.5 conditions. The open circuit voltage decay (OCVD) of the assembled QDSSCs is measured. The electron-hole pairs recombination processes are also studied.