In recent years, solar energy, particularly visible light has been exploited as one of critical sources to induce chemical transformation. Among the solar-capturing materials, inorganic semiconductors exhibit exceptional photophysical and optoelectronic properties and hence are widely employed in solar energy capture and conversion. Intrigued by photovoltaics performance of respective semiconductor materials, our lab hypothesized that such photoactive semiconductor materials that have been proven to be effective in solar cell capture should also be effective on photocatalytic organic reactions, since both of solar cell and photocatalysis rely on light-induced charge separation and transfer. My work here focused on employing nanocrystals (NCs, i.e., lead-halide perovskite, silicon) directly derived from solar cell materials as promising candidates towards photocatalytic organic synthesis. In this thesis, readily accessible lead halide perovskite NCs (ca. 2-100 nm) were introduced as a heterogeneous photocatalyst towards α-alkylation of aldehydes, N- heterocyclization, C-H activation, and C-O bond formation with high selectivity under visible light irradiation. In addition to perovskite colloidal NCs, element-abundant and environment-friendly Si NCs were next explored as a cost-effective photocatalyst for organic transformations. The Si QDs photocatalyst was synthesized from bulk silicon by high energy ball milling (HEBM) method under a mechanical force. We have explored Si QDs as a photocatalyst under visible light to induce [4+2] annulation with tertiary amines and Michael acceptors to construct pharmaceutically active tetrahydroquinoline scaffolds in mild conditions under blue LEDs. Our perovskites and silicon photocatalysts are fabricated by easily accessible methods and are promising photocatalysts for photocatalytic organic transformations.