Principles of solar panels

Tags: The principle of solar panels The basis of solar cell energy conversion is the photovoltaic effect of semiconductor PN junction. When light is irradiated on the semiconductor photovoltaic device, photons with energy greater than the silicon forbidden band pass through the anti-reflection film and enter the silicon, and photo-generated electron-hole pairs are excited in the N region, the depletion region, and the P region. Depletion zone: (Fig. 1) After the photogenerated electron-hole pair is generated in the depletion zone, it is immediately separated by the built-in electric field, the photogenerated electrons are sent into the N zone, and the photogenerated holes are pushed into the P zone. According to the depletion approximation condition, the carrier concentration at the boundary of the depletion region is approximately 0, that is, pu003dnu003d0. Fig. 1 (Fig. 2) In the N zone: After the photo-generated electron-hole pair is generated, the photo-generated hole diffuses to the PN junction boundary. Once it reaches the PN junction boundary, it is immediately affected by the built-in electric field and is affected by the electric field. The force draws for a drifting motion, crossing the depletion zone into the P zone, and the photo-generated electrons (multiple sons) are left in the N zone. In the P zone: the photogenerated electrons (minority sons) also enter the N zone due to diffusion and then drift, and the photogenerated holes (multiple sons) remain in the P zone. In this way, the accumulation of positive and negative charges is formed on both sides of the P-N junction, so that the N region stores excess electrons and the P region has excess holes. Thus, a photo-generated electric field is formed in the opposite direction to the built-in electric field. Fig. 21. In addition to partially offsetting the effect of the barrier electric field, the photogenerated electric field also makes the P zone positively charged and the N zone negatively charged. An electromotive force is generated in the thin layer between the N zone and the P zone. This is the photovoltaic effect. . When the battery is connected to a load, the photocurrent flows from the P area through the load to the N area, and the power output is obtained from the load. 2. If the two ends of the P-N junction are opened, the electromotive force can be measured, which is called the open circuit voltage Uoc. For crystalline silicon cells, the typical value of the open circuit voltage is 0.5 to 0.6V. 3. If the external circuit is short-circuited, a photocurrent that is proportional to the incident light energy flows in the external circuit, and this current is called the short-circuit current Isc. Factors affecting photocurrent: 1. The more electron-hole pairs generated by light on the interface layer, the greater the current. 2. The more light energy the interface layer absorbs, the larger the interface layer, that is, the larger the cell area, and the larger the current formed in the solar cell. 3. The N area, depletion area and P area of u200bu200bthe solar cell can all generate photogenerated carriers; 4. The photogenerated carriers in each area must cross the depletion area before recombination in order to contribute to the photocurrent, so solve the actual problem The photogenerated current must take into account various factors such as generation and recombination, diffusion and drift in each zone.