<p>The electronic structure of semiconductor materials governs the law of electron motion, which profoundly affects the properties such as conductivity and photoelectric conversion. Photo-responsive single-molecule junction technology provides insights into the electronic structure of photogenerated substances at the molecular scale, enabling the characterization of dynamic processes such as charge separation and energy transfer. These processes involve the unique quantum state known as the “exciton”. The electrical characterization technique based on single molecule break junction facilities direct measurement of the photoelectric response of molecules at nanometer and subnanometer scale. This study reviews recent research progress of exciton effects and the characterization of optoelectronic phenomena. The mechanisms of exciton effects in three key optoelectronic phenomena—photoconductivity, photovoltaics, and photoluminescence—are discussed. Furthermore, advanced spectral characterization techniques applied to the in-situ monitoring of single-molecule optoelectronic devices are highlighted. These include Raman spectroscopy with various enhancements, inelastic electron tunneling spectroscopy, and ultrafast spectroscopy with high resolution.</p>