Si-Doping Effects in Cu(In,Ga)Se₂ Thin Films and Applications for Simplified Structure High-Efficiency Solar Cells

Abstract

We found that elemental Si-doped Cu(In,Ga)Se (CIGS) polycrystalline thin films exhibit a distinctive morphology due to the formation of grain boundary layers several tens of nanometers thick. The use of Si-doped CIGS films as the photoabsorber layer in simplified structure buffer-free solar cell devices is found to be effective in enhancing energy conversion efficiency. The grain boundary layers formed in Si-doped CIGS films are expected to play an important role in passivating CIGS grain interfaces and improving carrier transport. The simplified structure solar cells, which nominally consist of only a CIGS photoabsorber layer and a front transparent and a back metal electrode layer, demonstrate practical application level solar cell efficiencies exceeding 15%. To date, the cell efficiencies demonstrated from this type of device have remained relatively low, with values of about 10%. Also, Si-doped CIGS solar cell devices exhibit similar properties to those of CIGS devices fabricated with post deposition alkali halide treatments such as KF or RbF, techniques known to boost CIGS device performance. The results obtained offer a new approach based on a new concept to control grain boundaries in polycrystalline CIGS and other polycrystalline chalcogenide materials for better device performance.

Group III Elemental Composition Dependence of RbF Postdeposition Treatment Effects on Cu(In,Ga)Se2 Thin Films and Solar Cells

“…The values of ε CIGS ∼ 13.5 and ε CGS ∼ 11.5 were used in this study. Detailed characterization conditions can be found elsewhere …”

Limitation of Current Transport across the Heterojunction in Cu(In,Ga)Se2Solar Cells Prepared with Alkali Fluoride Postdeposition Treatment

“…Regarding the effects of alkali fluoride PDT on device parameters, an increase in the open-circuit voltage (V oc ) has been observed consistently, whereas short-circuit current ( J sc ) and fill factor (FF) present an inconsistent trend in different contributions. [2][3][4][5][6][7][8][9] For the context of this work, we note that some publications have reported the presence of a barrier for the bucking and/or photo current, resulting for instance in a rollover of the current-voltage ( J-V ) characteristics or a crossover between dark and light J-V curves after PDT. [7][8][9][10] Various studies on the incorporation of alkalis can be found in the literature.…”

“…[2][3][4][5][6][7][8][9] For the context of this work, we note that some publications have reported the presence of a barrier for the bucking and/or photo current, resulting for instance in a rollover of the current-voltage ( J-V ) characteristics or a crossover between dark and light J-V curves after PDT. [7][8][9][10] Various studies on the incorporation of alkalis can be found in the literature. Attempts have been made to explain changes in electronic properties and performance of the solar cell from these fundamental investigations.…”

Temperature‐dependent current–voltage and admittance spectroscopy analysis on cesium‐treated Cu (In1 − x,Gax)Se2 solar cell before and after heat‐light soaking and subsequent heat‐soaking treatments

“…This result is consistent with other studies. 58,59 This is expected to be due to the occupation of the CIGS/Mo interface with heavier alkali metals 8 …”