Monodispersed bandgap tunable lead sulfide nanocrystals ranging from 0.6 to 1.7 eV have been synthesized by adjusting the reaction temperature and growth time. An evolution from cuboctahedra to perfect cube takes place at higher reaction temperature with longer annealing time. The nanocrystals absorb light both in the visible and IR spectral range. Bandgap dependent photovoltaic studies reveal optimal device performance for a critical size nanocrystal with 1.2 eV bandgap revealing the role of optimum bandgap on the photovoltaic performance.