Original Theoretical Framework for Quantum Dot Solar Cell Efficiency Enhancement Through Plasmonic Nanostructure Integration for Tropical Climate Applications

Quantum dot solar cells offer theoretically superior photon harvesting through quantum confinement-tunable bandgaps and the potential for multiple exciton generation, yet practical efficiencies remain below theoretical limits due to poor light absorption in thin active layers. Plasmonic metal nanostructures can concentrate electromagnetic fields near quantum dot absorbers through localized surface plasmon resonance, potentially bridging this efficiency gap. This research develops an original theoretical framework for quantifying plasmon-enhanced light absorption in quantum dot solar cells, with experimental validation directed toward high-efficiency devices optimized for the tropical solar spectrum of Nigeria. The theoretical framework extends classical Mie scattering theory to account for quantum confinement corrections to the quantum dot polarizability and derives coupled dipole equations for the collective optical response of quantum dot-metal nanoparticle heterostructures. Optical generation rate enhancement factors are computed using a finite-difference time-domain electromagnetic simulation framework developed in-house at Ahmadu Bello University, Zaria. CdSe/ZnS core-shell quantum dots synthesized at the laboratory and gold nanoparticles of 20, 40, and 80 nm diameter were co-deposited to fabricate experimental devices. Under AM1.5 illumination, quantum dot devices with 40 nm gold nanoparticle plasmonic enhancement layers showed external quantum efficiency enhancement of 38 percent in the 450 to 600 nm wavelength range compared to reference devices without nanoparticles. The framework correctly predicts the observed wavelength-selective enhancement using an analytical near-field enhancement integral derived as an original contribution. Potential power conversion efficiency gains for equatorial Nigerian insolation conditions are modeled. Keywords: quantum dot, solar cell, plasmon, nanostructure, photovoltaic efficiency