The performance of colloidal quantum dots (CQD) solar cell lags behind due to the carrier recombination within the quasi-neutral region (QNR). To overcome such issues, researchers exploited graded band alignment technique by piling CQDs of different size. In addition, the electron and hole transport layers, i.e., ETL and HTL highly impact the performance of CQD devices. Therefore, in this work, performance assessment of MgZnO (MZO) and TiO2 ETL based PbS CQD solid layer treated with tetrabutylammoniym iodide (PbS-TBAI) absorber layer based solar cell device is carried out to achieve > 13% power conversion efficiency (PCE). In the initial steps, calibration has been done to achieve the state of the art PCE of 9.4%, followed by device optimization. The optimisation is carried out in term of doping density of HTL and ETL, and a device is finalised with doping density of 5 x 10(17) cm(-3) for both, ETL and HTL. MZO and TiO2 ETL based devices with said doping reflected 13.59% and 13.94% conversion efficiencies. The influence of PbS-TBAI/ETL interface defect density (IDD) has also been studied where IDD is varied from 1 x 10(13) cm(-2) to 1 x 10(18) cm(-2) while keeping the rest of the device parameters intact. The results show a noteworthy reduction in the PV performance of the device at higher IDD. External quantum efficiency (EQE) is also obtained to understand the carrier collection. The result shows that carrier collection reduces particularly at lower wavelengths, i.e., < 600 nm while increasing the IDD from 1 x10(13) cm(-2) to 1 x 10(18) cm(-2). Whereas, the insignificant reduction is observed at higher wavelengths, i.e. > 600 nm. To understand the carrier dynamics for the correlation of the data, energy band diagram (EBD) is obtained for all the performed variation. All the study reported is performed using SCAPS-1D simulator.