Chapter 545 253 Lift, It Can All Be Lifted (8.2K)_5

Alright. Let's return our gaze to the original scene. The photovoltaic effect, in a strict sense, doesn't have too direct a relationship with wave theory, yet it's an indispensable step. Firstly, it provides a transitional thought process, preventing these bosses from sudden heart attacks upon witnessing certain phenomena and thus averting a tragedy in the history of human science. Moreover, it serves to... inspire Old Fa. Don't forget, the concept of semiconductors was proposed by Old Fa. Look at him now, shaking like Second Brother Wu, akin to a 'sudden revelation' moment in a fantasy novel, right? Subsequently, several professors gathered around the electrolysis cell again, observing the phenomenon for a while. Stokes even reached out to touch the platinum electrode plate, quickly withdrawing his finger with a swoosh. (Not recommended to try, feels somewhat like a metallic host chassis leaking electricity; don't ask how I know, just ask, and I'll say it was from back when I was stubborn) "Truly bizarre..." Stokes murmured, frowning as he rubbed his tingling fingers, "Why does shining light on a platinum electrode generate a current within the solution?" "According to Mr. Ampere's theory, the illumination created a closed circuit with a potential difference inside the electrolysis cell?" Another professor stepped forward two steps; his name is Bart Briggs, who ranks among the top five physics experts at the University of Cambridge today. He analyzed, "Could it possibly be due to a thin layer of impurities on the plate's surface? Such as being doped with a thermal effect?" Old Fa quickly shook his head, denying this speculation: "The light from a flashlight shouldn't reach the magnitude required to induce changes in a thin layer of impurities; at most, bromides and iodides might briefly decompose to produce an electrical effect, but it cannot continue long-term." Then he glanced at Xu Yun, who appeared 'obedient.JPG', picked up a clean piece of platinum electrode from the table, slightly curled his long index finger, and tapped on it: "Therefore, it's evident that in metal plates like platinum electrodes, there must be conditions that can form an intrinsic field..." Seeing this, Stokes couldn't help asking, "Mr. Faraday, have you thought of something?" A hint of hesitation appeared on Old Fa's face, as if engaged in some internal debate, but he finally said, "Just some vague speculations..." "I wonder if there might be a possibility, for example, that within the platinum electrode, there originally exist certain electric charges, which maintain themselves in a relatively balanced closed state, thereby not exhibiting charged properties." "Under illumination, they get excited—or the balance is interrupted, resulting in a potential difference?" "But in this way, the actual environment invoked might be invisible to the naked eye..." Watching Old Fa speak eloquently, Xu Yun remained silent. However, his clenched fists revealed that his heart was not at peace at this moment. As everyone knows, the essence of the photovoltaic phenomenon lies in atomic energy band structure, involving concepts of valence bands and conduction bands. The so-called valence band refers to the area relatively close to the atomic nucleus. The electrons here are tightly held, unable to escape easily. The conduction band, on the other hand, is far from the atomic nucleus, where electrons are unregulated and relatively free. If an external electric field is applied, allowing these electrons to move, the material conducts electricity. Besides these two areas, there is also an area between the valence band and the conduction band. This area does not allow the existence of electrons, known as the forbidden band. So in the thermodynamic world, generally, there are two kinds of materials: one with a narrow or even nonexistent forbidden band. At room temperature, electrons on the outer layer of the valence band can easily transition to the conduction band. These are conductors. Conversely, if the material's forbidden band is wide, generally greater than three electron volts, at room temperature, electrons obediently stay on the valence band, unable to conduct electricity. These are insulators. And materials with an energy gap less than 3eV between the valence band and the conduction band are semiconductors. These electrons will form something called a PN junction, displaying different electrical properties at each end, thus forming an electric field pointing from N to P. This electric field forms spontaneously and is therefore called the conductor's built-in electric field. Regarding the role of the photovoltaic effect, it's to tempt those already paired valence band electrons again. In other words, valence band electrons absorb light energy, their energy becomes higher, and they transition to the conduction band. The holes left behind by electrons are influenced by the built-in electric field and are thrown to both sides, forming an electric field pointing from P to N. This is the photovoltaic electric field, opposite in direction to the built-in electric field. At this moment, as long as an external circuit is added, due to the presence of a potential difference, a current will be generated in the circuit. This is also the principle of photovoltaic power generation in later generations, except that its utilization rate has been low, so it remains a developing project. Back in 1850, Old Fa and his peers hadn't even discovered electrons; at most, Coulomb had proposed the concept of charge. There was still a long way to go to the real particles. Yet, Old Fa could connect the phenomenon to the internal 'junction', how could one not be amazed? In fact, this wasn't the first time Xu Yun encountered such a situation.