Exploration of AgBiS2 semiconductor thin films for efficient solar energy conversion and storage

AgBiS2 quantum dots (ABS QDs) have emerged as highly promising candidates for efficient solar energy conversion and storage applications due to their strong optical absorption, non-toxicity, and elemental availability. Nevertheless, the efficiencies currently fall far short of their thermodynamic limits, due in large part to sluggish charge transport characteristics in nanocrystal derived films. This thesis addresses this challenge by developing a multifaceted approach to tune the electronic and optical properties of ABS QDs, enabling the design of advanced semiconductor structures for photovoltaic and photoelectrochemical applications. The first major strategy involves tailoring the surface chemistry of ABS QDs through a solvent-induced ligand exchange (SILE) process. This approach systematically modulates the electronic properties of ABS films by regulating the ligand concentrations and types, facilitating the fabrication of planar p-n heterojunctions with favorable band alignment for solar cells. The resulting ultrathin (30 nm) ABS heterojunction absorber layers exhibit enhanced carrier transport and separation, driven by built-in electric fields, achieving a solar cell power conversion efficiency (PCE) of 7.43%. This work not only demonstrates the critical role of surface composition in controlling n- and p-type charge transfer doping but also provides a generalizable framework for junction engineering in semiconductor films. In addition, we explore thermal processing as a complementary strategy to tune the optoelectronic properties of ABS. Comprehensive characterization also reveals that thermally-induced defects reduce electron density, shifting the Fermi level (Ef) and promoting p-type behavior in ABS. While this p-type doping is advantageous for certain applications, preserving the n-type characteristics of ABS is essential for its use as a semiconductor photoanode. To address this, we develop a novel thermal treatment strategy combined with atomic layer deposition (ALD) to fabricate ABS/TiOx heterojunctions. The ALD process not only enhances light absorption but also introduces a protective TiOx layer that prevents defect formation, maintaining the n-type nature of ABS. The ABS/TiOx heterojunction achieves a five-fold increase in photocurrent density, reaching 600 μA cm-2 at 1.0 V vs. RHE, compared to 120 μA cm-2 for pristine ABS. This improvement is attributed to favorable band alignment and enhanced charge extraction. By integrating surface chemistry modulation approaches, cation-disorder engineering, and interfacial design, this thesis provides a comprehensive framework for optimizing the electronic and optical properties of ABS QDs. These insights enable the development of functional heterojunctions tailored for both photovoltaic and photoelectrochemical applications, advancing ABS as a versatile semiconductor for energy conversion and storage technologies.