In this paper, a mathematical model and the relevant computer code are developed to quantify the extraction probability rate of charge carriers (EPRCC) in a perovskite solar cell of the structure: Glass/ITO/PEDOT: PSS/CH3NH3PbI3/PC60BM/Al to investigate the influence of interfaces and grain boundaries. It is found that, without passivation, the probability of an electron generated near the anode reaches to the cathode is only 35%, while by passivating the interfaces and grain boundaries, this probability increases to about 60% at maximum power point condition. Likewise, without passivation, the probability of a hole generated near the electron transport layer-active layer interface reaches to the hole transport layer is only 15%, while by passivating the interfaces and grain boundaries, this probability increases to about 45% at maximum power point condition. The same calculation has been done at the short-circuit current condition, and it is found that at the maximum power point condition, passivation works better for increasing the EPRCC than at the short circuit current condition. The authors have also investigated the influence of grain boundary sizes on the EPRCC, and the results show that the EPRCC is almost grain boundary size independent.