Advanced Optoelectronic Design for Perovskite-Silicon Multijunction Solar Cells

The global energy transition demands scalable, efficient, reliable, and cost-effective photovoltaic technologies. Perovskite-silicon multijunction solar cells have emerged as leading candidates to surpass the efficiency limits of single-junction silicon (Si) photovoltaics. This thesis presents a comprehensive study focused on overcoming optoelectronic limitations in perovskite-silicon tandem and triple-junction devices. To address open-circuit voltage losses in wide-bandgap perovskite absorbers, photoluminescence quantum yield measurements identified interfacial recombination at the perovskite/C60 interface as a major bottleneck. A thin atomic layer deposited (ALD) insulating interlayer significantly reduced surface recombination velocity. The AlOx passivation enabled tandem cells with silicon heterojunction (SHJ) bottom cells to reach a certified efficiency of 29.9% and a fivefold improvement in stability. Although this approach enhanced open-circuit voltage (VOC) by 60 mV, full-area tunnel-oxide passivation introduced resistive losses, limiting fill factor (FF). To address this, a passivation scheme improving both interface and transport was developed using fluorinated benzyl phosphonic acid (pFBPA) in the precursor. This enabled ALD-AlOx-level passivation while minimizing resistive losses and improving the FF x VOC product. Void formation caused by the hydrophobic additive was mitigated using insulating SiOx nanoparticles to enhance wettability and film uniformity. This allowed integration with a high-performance self-assembled monolayer (Me-4PACz), yielding a certified 30.93% efficiency, the first perovskite-Si tandem to exceed 30% on front-flat bottom cells. Bulk limitations were then addressed through compositional engineering. A triple-halide triple-cation perovskite suppressed defects and improved energy alignment with C60. Combined with pFBPA and piperazinium halide, this surface and interface passivation (SIP) extended minority carrier lifetimes from 1.4 to 5.3 microseconds, forming a passivating contact similar to crystalline silicon cell technologies. Devices achieved certified VOC over 2.0 V and efficiencies above 31.5%. The strategy was scaled to 60 cm2 with 28.9% efficiency, demonstrating uniform passivation. Industrial relevance was shown with >30% efficiency on double-side nanotextured SHJ cells using thin Cz wafers, and >31% on front-textured tunnel oxide passivated contact cells. Device simplification was achieved by replacing the transparent conductive oxide interconnect with a p-doped nanocrystalline silicon layer, enabled by engineering the self-assembled monolayer to balance charge extraction and passivation. Finally, perovskite-perovskite-Si triple-junction cells were developed by addressing low VOC in the top-cell and limiting current density in the middle cell. Top-cell crystallization was tuned with an alkylamine additive, while the middle cell current was improved via a three-step fabrication process and SiOx-based mid