This work develops an optical-electrical coupled numerical model to simulate cubic MAPbI₃based perovskite solar cells (PSCs). Optically, the transfer matrix method resolves multilayer interference effects to obtain the spectrally resolved local absorbed power density and photo-generation rate. Electrically, the Poisson, drift-diffusion, and continuity equations are solved self-consistently, incorporating Shockley-Read-Hall, radiative, Auger, and interfacial recombination. On this basis, the power densities of individual loss channels, including thermalization, Joule, and recombination heat, are quantified within an isothermal framework, enabling a systematic evaluation of the device’s electrical output and energy loss allocation under different operating temperatures. The simulation results reveal that the photo-generation rate is governed by the absorption coefficient and local optical field, with the optimal response centered at 460 nm. Short-wavelength light (<400 nm) is confined near the incident surface due to parasitic absorption and shallow penetration, whereas long-wavelength light (>600 nm) suffers from reduced generation owing to weak intrinsic absorption. Electron and hole concentrations follow the same wavelength dependence, but band offsets introduce asymmetry. Electrons are rapidly extracted at the electron transport layer/perovskite absorber layer interface, causing a sharp concentration drop, whereas holes are depleted at the same interface by the electron transport layer valence band barrier and accumulate at the hole transport layer interface for efficient extraction. Compared with literature reports, the present device yields higher photo-generated current and open-circuit voltage because ion migration is excluded, whereas the literature device using ZnO/NiO_x transport layers, with their wide band-gaps and suitable band alignment, exhibits more efficient carrier extraction and lower contact resistance at low voltages, thus delivering a higher current density than the TiO₂/Spiro-OMeTAD combination adopted in this study. This advantage diminishes at higher voltages as the built-in field weakens, and both current densities converge near open-circuit voltage where recombination dominates. A peak efficiency of 22.4% at the maximum power point is achieved. Of the total incident energy, 78.4% is dissipated as losses, of which optical escape losses and Peltier heat together account for 58.5%, thermalization losses for 7.9%, and non-radiative surface recombination losses for 5.6%. Rising temperature reduces thermalization and Joule losses, leaves parasitic absorption nearly unchanged, but significantly increases bulk and surface recombination, leading to output power degradation. Thus, a synergistic approach combining optical, band, and interface engineering to suppress multiple loss channels offers a promising path for performance enhancement. This study provides a theoretical foundation for loss mitigation and optimization in PSCs.