Absorber composition: A critical parameter for the effectiveness of heat treatments in chalcopyrite solar cells

Post‐device heat treatment (HT) in chalcopyrite [Cu (In,Ga)(S,Se)2] solar cells is known to improve the performance of the devices. However, this HT is only beneficial for devices made with absorbers grown under Cu‐poor conditions but not under Cu excess. We present a systematic study to understand...

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Bibliographic Details
Published in:Progress in photovoltaics 2020-10, Vol.28 (10), p.1063-1076
Main Authors: Sood, Mohit, Elanzeery, Hossam, Adeleye, Damilola, Lomuscio, Alberto, Werner, Florian, Ehre, Florian, Melchiorre, Michele, Siebentritt, Susanne
Format: Article
Language:English
Subjects:
Absorbers
Buffer layers
Carrier density
Chalcopyrite
Chemical potential
Composition
Computer simulation
Copper
Copper indium selenides
CuInS2 solar cell
CuInSe2 solar cell
defect passivation
Devices
efficiency
Electrical measurement
Heat treatment
Mathematical models
Minority carriers
p+ layer
Passivity
Performance enhancement
Photovoltaic cells
quasi‐Fermi level
Selenides
Selenium
Shunt resistance
Solar cells
Temperature dependence
time‐resolved photoluminescence
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Summary:Post‐device heat treatment (HT) in chalcopyrite [Cu (In,Ga)(S,Se)2] solar cells is known to improve the performance of the devices. However, this HT is only beneficial for devices made with absorbers grown under Cu‐poor conditions but not under Cu excess. We present a systematic study to understand the effects of HT on CuInSe2 and CuInS2 solar cells. The study is performed for CuInSe2 solar cells grown under Cu‐rich and Cu‐poor chemical potential prepared with both CdS and Zn(O,S) buffer layers. In addition, we also study Cu‐rich CuInS2 solar cells prepared with the suitable Zn(O,S) buffer layer. For Cu‐poor selenide device, low‐temperature HT leads to passivation of bulk, whereas in Cu‐rich devices, no such passivation was observed. The Cu‐rich devices are hampered by a large shunt. The HT decreases shunt resistance in Cu‐rich selenides, whereas it increases shunt resistance in Cu‐rich sulfides. The origin of these changes in device performance was investigated with capacitance–voltage measurement, which shows the considerable decrease in carrier concentration with HT in Cu‐poor CuInSe2, and temperature‐dependent current–voltage measurements show the presence of barrier for minority carriers. Together with numerical simulations, these findings support a highly doped interfacial p+ layer device model in Cu‐rich selenide absorbers and explain the discrepancy between Cu‐poor and Cu‐rich device performance. Our findings provide insights into how the same treatment can have a completely different effect on the device depending on the composition of the absorber. The impact of heat treatment on device performance prepared with Cu‐rich and Cu‐poor CuInSe2 and CuInS2 absorber is studied. Improved performance of Cu‐poor devices worsened for Cu‐rich devices is observed. Experimental and numerical simulations suggest the presence of a highly doped p+ layer in case of Cu‐rich CuInSe2 device and explain the observed trends in device performance. By linking the absorber stoichiometry and post‐deposition treatments, this study provides insights for optimizing post‐deposition treatments for absorbers grown under different conditions.
ISSN:1062-7995
1099-159X
DOI:10.1002/pip.3314