Let me introduce you to what HJT cells are
HJT (Heterojunction) cells, also known as heterojunction solar cells, are based on N-type monocrystalline silicon. Thin silicon-based films with different properties are deposited on the front and back surfaces, along with transparent conductive films. A standard crystalline silicon solar cell is a homojunction cell, meaning the PN junction is formed on the same semiconductor material, whereas in a heterojunction cell, the PN junction is made of different semiconductor materials.
First, a very thin intrinsic amorphous silicon layer (i-a-Si:H) and a p-type amorphous silicon layer (p-a-Si:H) are deposited on the front surface of the N-type monocrystalline silicon (c-Si). Then, a very thin intrinsic amorphous silicon layer (i-a-Si:H) and an n-type amorphous silicon layer (n-a-Si:H) are deposited on the back surface of the silicon wafer to form a back surface field. Transparent conductive oxide (TCO) films are then deposited on both sides of the cell using PVD. TCO not only reduces the series resistance during current collection but also acts as an anti-reflection layer. Finally, metal electrodes are fabricated on the TCO.
The PN junction in a heterojunction cell consists of different semiconductor materials, forming a double heterojunction by inserting a thin layer of narrow-bandgap material between the wide-bandgap p-type and N-type semiconductor materials.
The HJT technology improves the passivation of the silicon surface by inserting intrinsic amorphous silicon as a buffer layer between the PN junctions, effectively addressing the high carrier recombination loss in the doped layers and substrate contact regions of conventional cells. This results in higher minority carrier lifetime and open-circuit voltage.