Soft, Organic, Carrier-Selective Contacts at Inorganic Semiconductor Interfaces Enabled by Low-Defect Covalent Bonding

Carl, Alexander D.

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Soft, Organic, Carrier-Selective Contacts at Inorganic Semiconductor Interfaces Enabled by Low-Defect Covalent Bonding

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The integration of covalent, organic, carrier-selective monolayers on semiconductor surfaces will enable efficient electron transfer in perovskite single and tandem-junction perovskite photovoltaic devices. This work details the functionalization and characterization of semiconductor surfaces and the electronic measurements of relevant devices. In chapter 3, we synthesized oxide-free, covalently-bound alkylamine terminated Si(111) surfaces. These surfaces demonstrated low recombination velocities and resistance to oxidation under ambient conditions. The NH3+-terminated monolayers also showed increased adhesion toward MAPbI3 thin films and the photovoltaic performance of the perovskite on functionalized n+-Si was increased compared to the native oxide. Chapter 4 details the covalent functionalization of oxidized Si(111) and TiO2 surfaces with perylene derivatives. Secondary functionalizations enabled surface coverage quantification relevant to the surface density ammonium groups that might later be utilized in MAPbI3 devices. Chapter 5 utilizes the chemical strategies developed in Chapter 4 to prepare NH3+-terminated, perylene monolayers on TiO2 for the testing of their viability as electron transport layers in MAPbI3-based PV devices. We characterized the band-energy levels as the TiO2 was functionalized and found the surface’s conduction band was well matched for use as an ETL in perovskite PV. Functionalized TiO2 devices showed increased performance compared to baseline, silane-functionalized TiO2-perovskite devices. Chapter 6 summarizes our latest work and future directions on perylenefunctionalized TiO2 perovskite devices and our exploration of oxide-free, ammonium-terminated, perylene monolayers on Si(111) surfaces for their viability in perovskite/silicon hetero-junction PV.

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