In the solar cell the static electric field keeps main role to generate the (photo) voltage. The static electric field is been produced by carriers (electrons) transporting from one side to other side. I have prepared heterojunction solar cells by chemical methods. There was no static electric field (as well as depletion region) in some heterojunctions. We had decided it was matching problems in the contact region of the materials (n & p type semiconductors).
Not knowing the material you are working with and their electrical/semiconductor properties, layer thickness, Ohmic contact materials and other information on the film, it is impossible to comment. Not sure what you mean by "We had decided it was matching problems in the contact region of the materials (n & p type semiconductors)." Please clarify so you may get help from the community.
I had fabricated CuxO-ZnO heterojunction for solar cell application in which CuO of drop-chemical method and ZnO of electrochemical deposition method. During the measuring of I-V there was no current for +1 or -1 voltage initially in the first time case (Figure attached). The I-V was normal for next cases. Our computerized power-supply started to supply voltage from +1 or -1 (i.e. not from zero). We were strange for the initial behavior of the curve. Therefore we had decided there is no depletion region in the initial stage.
Sorry but I am not getting what is the meaning of matching problem. IV characteristic is very similar to a diode like IV. So it can be thought as one layer is having hole as the majority carrier while other is having electron as majority carrier. So it is hard to say there is no depletion region. If you will draw the band diagram of the device you have made, you will probably get the answer that whether depletion region is expected or not.
When you say, during first measurement of IV there was no current in the device, it may be that contacts were not proper at that time.
Hope this helps
Not knowing the material you are working with and their electrical/semiconductor properties but in general it is possible that by selection of two layers with a lattice constant a close or by making the initial layer porous to reduce the mismatch between the junction layers
Generally, the interfacial mismatching between tow kind of materials will cause a carrier recombination, in which a lower Voc or a built-in field can not be measured under light irradiation. But not only this reason, it is a complicate materials science or PV device ptoblem. Pls try to read some books or relative documents,such as PV physics or semiconductor physics, so that you could understand them in detail.
Another fact:
The absorber layer (CuxO) showed very good photo sensitivity individually. Photo current is been increased in mA range under photo electrochemical measurement but it is been increased in μA range for the case of solar cell.
Both deposition methods are "wet" ones. In film pinholes you have residuals of initial solution. The post deposition treatment and drying is wery important.
You have heterostructure with uncontrolled electrolyte insite. When apply voltage a electrochemical reaction will start. The heterostructure current increase till 0.8 V (water decomposition). Bubbles occurs and break the electrical circuit.
Individually films fabricated by "wet" method may have good performance but in heterostructures occurs problems of electrolyte residuals.
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