We are introducing here hybrid Stranski Krastanov (SK) on submonolayer (SML) quantum dot (QD) heterostructure for improved photovoltaic energy conversion in the near infrared (NIR) region. Vertically coupled QDs with lower amount of cumulative strain make it a promising competitor of homogeneous QD families. Still now no research groups have reported such heterogeneously coupled QD based quantum dot solar cell (QDSC) for better NIR harvesting. In the present study, we are emphasizing on growth optimization of such heterogeneous QD family. Ex situ modulation of interdot electronic interaction has been explored by rapid thermal annealing (RTA). The sample with 0.1 ML/s growth rate and 7.5 nm GaAs barrier comes out as the best coupled configuration with improved thermal stability. This particular configuration is incorporated into a P-I-N QDSC, which shows broader and enhanced external quantum efficiency at NIR region. In addition, RTA at 650 and 700 degrees C shows a drastic enhancement of quantum efficiency due to the annihilation of as grown defects and trap centers.