- Introduction to Cells
(1) Overview: Cells are the core components of photovoltaic power generation, and their technical route and process level directly affect the power generation efficiency and service life of photovoltaic modules. Photovoltaic cells are located in the middle reaches of the photovoltaic industry chain. They are semiconductor thin sheets that can convert the sun’s light energy into electrical energy obtained by processing single/poly crystalline silicon wafers.
The principle of photovoltaic power generation comes from the photoelectric effect of semiconductors. Through illumination, a potential difference is generated between different parts of in homogeneous semiconductors or semiconductors combined with metals. It is converted from photons (light waves) into electrons and light energy into electrical energy to form a voltage. and current process. The silicon wafers produced in the upstream link cannot conduct electricity, and the processed solar cells determine the power generation capacity of photovoltaic modules.
(2) Classification: From the perspective of substrate type, cells can be divided into two types: P-type cells and N-type cells. Doping boron in silicon crystals can make P-type semiconductors; doping phosphorus can make N-type semiconductors. The raw material of P-type battery is P-type silicon wafer (doped with boron), and the raw material of N-type battery is N-type silicon wafer (doped with phosphorus). P-type cells mainly include BSF (conventional aluminum back field cell) and PERC (passivated emitter and rear cell); N-type cells are currently more mainstream technologies are TOPCon (tunneling oxide layer passivation contact) and HJT (intrinsic thin film Hetero junction). The N-type battery conducts electricity through electrons, and the light-induced attenuation caused by the boron-oxygen atom pair is less, so the photoelectric conversion efficiency is higher.
3. Introduction of PERC battery
(1) Overview: The full name of the PERC battery is “emitter and back passivation battery”, which is naturally derived from the AL-BSF structure of the conventional aluminum back field battery. From a structural point of view, the two are relatively similar, and the PERC battery only has one more back passivation layer than the BSF battery (the previous generation battery technology). The formation of the rear passivation stack allows the PERC cell to reduce the recombination speed of the back surface while improving the light reflection of the back surface and improving the conversion efficiency of the cell
(2) Development history: Since 2015, domestic PERC batteries have entered a stage of rapid growth. In 2015, domestic PERC battery production capacity reached the first place in the world, accounting for 35% of the global PERC battery production capacity. In 2016, the “Photovoltaic Top Runner Program” implemented by the National Energy Administration led the official start of industrialized mass production of PERC cells in China, with an average efficiency of 20.5%. 2017 is a turning point for the market share of photovoltaic cells. The market share of conventional cells began to decline. The domestic PERC cell market share increased to 15%, and its production capacity has increased to 28.9GW;
Since 2018, PERC batteries have become the mainstream in the market. In 2019, the large-scale mass production of PERC cells will accelerate, with a mass production efficiency of 22.3%, accounting for more than 50% of production capacity, officially surpassing BSF cells to become the most mainstream photovoltaic cell technology. According to CPIA estimates, by 2022, the mass production efficiency of PERC cells will reach 23.3%, and the production capacity will account for more than 80%, and the market share will still rank first.
4. TOPCon battery
(1) Description: TOPCon battery, that is, the tunneling oxide layer passivation contact cell, is prepared on the back of the battery with an ultra-thin tunneling oxide layer and a layer of highly doped polysilicon thin layer, which together form a passivation contact structure. In 2013, it was proposed by the Fraunhofer Institute in Germany. Compared with PERC cells, one is to use n-type silicon as the substrate. Compared with p-type silicon cells, n-type silicon has a longer minority carrier life, high conversion efficiency, and weak light. The second is to prepare a passivation layer (ultra-thin silicon oxide SiO2 and doped poly silicon thin layer Poly-Si) on the back to form a contact passivation structure that completely isolates the doped region from the metal, which can further reduce the back surface. The minority carrier recombination probability between the surface and the metal improves the conversion efficiency of the battery.
Post time: Aug-29-2023