Dear Vennhanna,

You questions needs pages long to answer it. I will try to answer the first part in my first comment ;

I order to draw the energy band diagram, you need ton prepare and energy level diagram for all materials in the solar cells with the energy levels referenced to the vacuum level. This will be the energy level diagram before contacting the materials. For every material you must indicate the EC, Ev and the Fermi level and the intrinsic level.

Then after contacting the materials and assuming that they come to thermal equilibrium, then the Fermi level will be flat through out the whole solar cells across all layers.

You have to consider that the a-Si undoped will be an intrinsic material having its Fermi level coinciding with Ei the intrinsic level. Its Eg the energy gap is about 1.6 eV,. The n+ a -Si is heavily doped amorphous silicon having its Fermi level very near to the conduction band edge. This is also valid for the p+ a-Si with its frmi level near to the valence band edge of the material. The a-Si i-layers are thought as passivation layers for the interface states at the heterojunctions between the single crystal silicon and the heavily doped a-Si. This structure is characterized by wide gap emitters thank to the higher energy gap of the a -silicon. Therefore the recombination current in the emitters will be reduced compared to the convention homojunction solar cells.

Otherwise there will be a transition region between the p+ emitter and the n-substrate material as in the conventional p-n junction. The n+ i N is a backsurface field junction of the type low -high junction where the holes will be reflected back to bulk reducing the recombination losses at the such contact.This also in addition to the hole reflection because of the wide gap of the a-Si layer.

The rest of the operation is very similar to the conventional homo junction solar cell.

Please draw the energy level diagram before and after the contacting and prsenet it for reviewing.

Best wishes

Thank you sir Abdelhalim abdelnaby Zekry for your reply. I have attached diagrams of band bending of homo junction and heterojunction. Due to discontinuity, recombination losses reduced in heterojunctions. I understood band bending and charge transport phenomena in homo and heterojunction solar cells.

Main issue is how to represent band bending of particularly IBC-SHJ solar cells ??since TCO is deposited on front side of c-Si and both emitter and BSF deposited back side of c-Si. From schematic structure of IBC-SHJ solar cell, I can see generated electrons and holes travel horizontally, electrons go to BSF side and holes go to emitter side in case of n-type c-Si absorber.

But, How to explain through band bending diagram ???

Wonderful Venkanna,

You drew the energy band diagram very well.

I would like to tell you that there is no transparent conductive oxide on the front region. The from layer must be a passivaion layer such as a-Si and antireflective coating oxide. So it could be ideally a silicon surface with zero recombination.

So, the the heterojunctions are lateral at the backside. They have to be made no distant larger than the diffusion length. So, excess electrons and holes in the volume above the heterojunctions a n+Si- nSI- a p+ Si will be collected by diffusion. to the interfaces.

You can draw the interfaces side by side and you will see that the excess charges will diffuse and be collected by the heterofaces.

Best wishes

The band diagram of IBC-SHJ is the same principle as the conventional solar cells. You don't have the choice : put the bulk on the middle, the n-contact on one side, and the p-contact on the other.

You can consult the paper bellow.

Good continuation.

Thank you madam @Rahal Saddula Leila