There are two types of solar cell structures according to the junction type of the solar cell. There is the homo junction solar cells where the junction is made in the same active material and in this case it is a p-n junction such as the crystalline or semicrystalline solar cells such as silicon and GaAs solar cells.

In case of not possible to produce homo p-n junction inn the semiconductor material one has to build hetero junction from two different semicondcutor materials or even from a metal and a semicondcutor material. The active material may be intrinsic such as the amorphous silicon or the organic or the perovskite semiconductor material. In order to build a field region one has to sand witch such i-material between an n-type material from one side and p-type material from the other side and make them heavily doped to achieve the highest contact difference of potential between them for the realization of relatively high open circuit voltage. This will be a form of pin structure. with two hetero junctions the p-i and the n-i junctions. In the literature of the solar cells, the p-layer is termed the hole transport layer and the n-layer is called the electron transport layer. In order to satisfy their function their energy levels must match the active layer. In the sense the conduction band edge of the ETL must lie slightly under the condcution band edge of the active layer in order to extract the electrons in the active layer. The ETL valence band edge must lie much under the valence band edge of the active layer to reflect the holes in the direction of the HTL.

Opposite conditions must exist in the HTL to extract the holes and reflect the electrons back in the active layer. In this way the maximum contact difference of potential that can be achieve is equal or slightly smaller than the energy gap of the active layer.

In case of homojunction one can not achieve as high as bandgap contact difference of potential because one can not heavy dope the material to the degree of degeneracy because this brings the socalled heavy doping effects.

In fact the heavy doping effects in the homojunctions was one of the drivers of heterojunctions where one uses widegap material as emitters for the bipolar transistors and solar cells.

The heavy doping effects is to reduce the minority carrier lifetime and cause bandgap narrowing.

So, heterojunctions are used whenever one can not produce technologically p-n homojunctions or to over come the heavy doping effects in homo-junctions.

This is the case in for the organic semicondcutor materials and perovskite semiconductors.

Best wishes

There are two types of solar cell structures according to the junction type of the solar cell. There is the homo junction solar cells where the junction is made in the same active material and in this case it is a p-n junction such as the crystalline or semicrystalline solar cells such as silicon and GaAs solar cells.

In case of not possible to produce homo p-n junction inn the semiconductor material one has to build hetero junction from two different semicondcutor materials or even from a metal and a semicondcutor material. The active material may be intrinsic such as the amorphous silicon or the organic or the perovskite semiconductor material. In order to build a field region one has to sand witch such i-material between an n-type material from one side and p-type material from the other side and make them heavily doped to achieve the highest contact difference of potential between them for the realization of relatively high open circuit voltage. This will be a form of pin structure. with two hetero junctions the p-i and the n-i junctions. In the literature of the solar cells, the p-layer is termed the hole transport layer and the n-layer is called the electron transport layer. In order to satisfy their function their energy levels must match the active layer. In the sense the conduction band edge of the ETL must lie slightly under the condcution band edge of the active layer in order to extract the electrons in the active layer. The ETL valence band edge must lie much under the valence band edge of the active layer to reflect the holes in the direction of the HTL.

Opposite conditions must exist in the HTL to extract the holes and reflect the electrons back in the active layer. In this way the maximum contact difference of potential that can be achieve is equal or slightly smaller than the energy gap of the active layer.

In case of homojunction one can not achieve as high as bandgap contact difference of potential because one can not heavy dope the material to the degree of degeneracy because this brings the socalled heavy doping effects.

In fact the heavy doping effects in the homojunctions was one of the drivers of heterojunctions where one uses widegap material as emitters for the bipolar transistors and solar cells.

The heavy doping effects is to reduce the minority carrier lifetime and cause bandgap narrowing.

So, heterojunctions are used whenever one can not produce technologically p-n homojunctions or to over come the heavy doping effects in homo-junctions.

This is the case in for the organic semicondcutor materials and perovskite semiconductors.

Best wishes

Hello! Yes it is very imporent becouse in heterojunction is more effective then homojunction. İ can explane coase of this, but i will not to do that. In literature, prosess of working of heterojunction writen very good.

Heterojunction solar cells are very important to increase the current density with respect to the area, efficiency and Fillfactor.

Dear Ayesha,

Welcome,

At first i would like to thank you for recommending my answer.

There is a major problem with the heterojunctions that as it is formed from two different materials with different lattice constants, there will be a high density of interface states that can act as active recombination centers leading to a reduction in the lifetime of minority charges. The result is an appreciable recombination losses at these interfaces leading to increase the dark current in solar cells and reduce the photo current. This problem lasted long time till one could passivate these interface states to render them inactive. In homojunctions such interface are not existing and thereby there is no interface recombination losses.

For more information on heterojunctions please see the paper:Article M. Abdelnaby, A. Zekry, F. Elakkad and H. F. Ragaie, “ Depen...

Best wishes

Thanks Prof. A. Zekry and thank you very much for your brief answers, they have been very useful to me.