Dear Helen,

welcome,

The recombination in volume or at the interface of a heterojunction has two effects:

It can decrease the collected shortcircuit current and make it smaller than the photocurrent Iph which is the highest photocurrent to be collected.

But this reduction is observable when the built electric field can not dispatch the photogenrated electrons and holes before they recombine that is in their lifetime in the drift region. Or they can not diffuse to the field separation region before they recombine. This for the shortcircuit current.

It will only affected when the photogenerated carriers can no be collected before recombination.

- The other effect on the dark current specifically in the reverse saturation current.

The dark current is always suffering from the recombination either in the bulk or at the interface. It is so that the reverse saturation current increases with the decrease of the minority carrier lifetime in the volume or the increase of the recombination velocity at the surface.

This is the case when the solar cell can be modeled by a single diode model.

It is so that there is nonideal solar cell performance which makes it deviate from the single junction model. The presence of shunting resistance reduces the opencircuit voltage while will not affect the shortcircuit current to the great extent.

The presence of nonlinear ohmic consonants can reduce the fill factor and the shortcircuit current.

I would like that you follow my paper: https://www.researchgate.net/publication/232710742_M_Abdelnaby_A_Zekry_F_Elakkad_and_H_F_Ragaie_Dependence_of_dark_current_on_zine_concentration_in_Znx_Cd1-x_SZn_Te_hetero_-_junctions_Solar_Energy_Materials_and_Solar_Cells_29_1993

In spite of its importance very few researchers who payed attention to it.

and the complementary paper:

Article A. Zekry and G. El-Dllal, “ effect of MS contact on the elec...

I devoted my self very early to explain the odd electronic phenomena in solar cells. The time came where these phenomena are evident in the new solar cell structures.

Helen if you find them useful recommend them for your colleagues and your students.

Best wishes

Dear Helen,

welcome,

The recombination in volume or at the interface of a heterojunction has two effects:

It can decrease the collected shortcircuit current and make it smaller than the photocurrent Iph which is the highest photocurrent to be collected.

But this reduction is observable when the built electric field can not dispatch the photogenrated electrons and holes before they recombine that is in their lifetime in the drift region. Or they can not diffuse to the field separation region before they recombine. This for the shortcircuit current.

It will only affected when the photogenerated carriers can no be collected before recombination.

- The other effect on the dark current specifically in the reverse saturation current.

The dark current is always suffering from the recombination either in the bulk or at the interface. It is so that the reverse saturation current increases with the decrease of the minority carrier lifetime in the volume or the increase of the recombination velocity at the surface.

This is the case when the solar cell can be modeled by a single diode model.

It is so that there is nonideal solar cell performance which makes it deviate from the single junction model. The presence of shunting resistance reduces the opencircuit voltage while will not affect the shortcircuit current to the great extent.

The presence of nonlinear ohmic consonants can reduce the fill factor and the shortcircuit current.

I would like that you follow my paper: https://www.researchgate.net/publication/232710742_M_Abdelnaby_A_Zekry_F_Elakkad_and_H_F_Ragaie_Dependence_of_dark_current_on_zine_concentration_in_Znx_Cd1-x_SZn_Te_hetero_-_junctions_Solar_Energy_Materials_and_Solar_Cells_29_1993

In spite of its importance very few researchers who payed attention to it.

and the complementary paper:

Article A. Zekry and G. El-Dllal, “ effect of MS contact on the elec...

I devoted my self very early to explain the odd electronic phenomena in solar cells. The time came where these phenomena are evident in the new solar cell structures.

Helen if you find them useful recommend them for your colleagues and your students.

Best wishes

Thank you again Professor Abdelhalim abdelnaby Zekry ! Your explanation is very helpful to me and my colleages, but generated more questions too!

If you refer to the attached JV scan from the paper referenced by Habib M. N. Ahmad , based on your explanation of how recombination at the junction interface (and bulk) will increase the reverse saturation current and thus reduce JSC (and VOC), why does Fig 2a (attached to this post) show that when the n-buffer layer is changed, which changes the surface recombination velocity at the junction interface, but the JSC was found to remain relatively unchanged?

We think it is explained in your sentences:

"But this reduction is observable when the built electric field can not dispatch the photogenrated electrons and holes before they recombine that is in their lifetime in the drift region. Or they can not diffuse to the field separation region before they recombine. This for the shortcircuit current. "

but we cannot yet understand what this means...

Any clarification is greatly appreciated!

Dear Helen,

welcome again,

I would like that you display the dark current on the same figure of the illuminated I-V curves of the solar cells. This will tell us many things about the interface recombination in relation to the drift current in the space charge region.

But i like to pay your attention about the change of the contact difference of potential between the two side of the junction when you change the buffer layer.

Keeping the absorber layer the same and increasing the contact difference of potential will keep the Isc constant and changes the open circuit voltage.

Best wishes

Dear Helen,

In effective photodiode (heterophotodiode) (PV cell) all must be perfect both p-n junction and interfaces between layers form PV cell. The matter is possible serious dependence of dark current (and hence VOC) of PV cell on recombination rate on interfaces involved in PV cell operation. There are two reasons of improving VOC when interfacial recombination rate lowered (improved):

1. Interfacial recombination channel with high rate acts as generator (injector) of eccess charge carriers which then separated by p-n junction; that leads to growth of dark current and lowering VOC.

2. Interfacial recombination channel with high rate makes spectral sensitivity curve of PV cell narrower, especially in wavelength range shorter than maximum. Therefore, your PV cell with unperfect interfaces will use only part of incoming optical radiation and will convert absorbed optical radiation with worser effectivity (may be a few times worser) and provide lower VOC.

You can find our article concerned discussed problem in photodiodes based MCT multylayer heterostructures (available on my RG page):

Contribution of generation-recombination processes at inner interface of MBE-grown Hg1-xCdxTe heterostucture to dark current of small active area photodiode

NB Due to high rate interfacial recombination dark current can grow on 2-3 orders of magnitude in our case.

Voc is nothing but accumulation of charges without recombination or improvement of potential energy. If one can suppressed the carrier recombination means less loss of carrier that ultimately success to improve Voc. This is simple way to answer.