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Potassium Treatments for Solution-Processed Cu(In,Ga)(S,Se) <sub/>2</sub> Solar Cells
摘要： Cu(In,Ga)(S,Se)2 (CIGSe, CIGSSe) has emerged as an attractive thin-film solar cell absorber material owing to its high light absorption coefficient and tunable bandgap. In CIGSSe processing and fabrication, the use of alkali treatments has been implemented as sodium doping is considered a requirement for high efficiency CIGSSe solar cell devices and has been used extensively. One of the more significant developments in recent years has been the discovery of the beneficial effects that potassium post-deposition treatments have on vacuum-processed CIGSSe solar cells as they are responsible for a major increase in CIGSSe solar cell performance. Here, we conduct a study of the effect of potassium treatments to solution-processed CIGSSe films grown from colloidal sulfide-based nanoparticle inks. By adding potassium through e-beam evaporation of KF prior to selenization and grain growth, we find that the grain growth of CIGSSe is enhanced with potassium addition and that a larger-grained film results compared to untreated selenized CIGSSe film, similar to what is observed in sodium-treated films. We also observe through XPS that films treated with K show the presence of the high-bandgap K-In-Se surface phase. Fabricating devices, we find that films that have been subjected simultaneously to both sodium and potassium treatments have enhanced optoelectronic performance mainly manifested in higher open-circuit voltage and higher short-circuit current.
关键词： CIGS,alkali treatment,Cu(In,Ga)(S,Se)2,solution-processed solar cells,potassium fluoride,chalcopyrite solar cell,sodium fluoride
更新于2025-09-23 15:21:01
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Heavy Alkali Treatment of Cu(In,Ga)Se <sub/>2</sub> Solar Cells: Surface versus Bulk Effects
摘要： Chalcopyrite solar cells achieve efficiencies above 23%. The latest improvements are due to post-deposition treatments (PDT) with heavy alkalis. This study provides a comprehensive description of the effect of PDT on the chemical and electronic structure of surface and bulk of Cu(In,Ga)Se2. Chemical changes at the surface appear similar, independent of absorber or alkali. However, the effect on the surface electronic structure differs with absorber or type of treatment, although the improvement of the solar cell efficiency is the same. Thus, changes at the surface cannot be the only effect of the PDT treatment. The main effect of PDT with heavy alkalis concerns bulk recombination. The reduction in bulk recombination goes along with a reduced density of electronic tail states. Improvements in open-circuit voltage appear together with reduced band bending at grain boundaries. Heavy alkalis accumulate at grain boundaries and are not detected in the grains. This behavior is understood by the energetics of the formation of single-phase Cu-alkali compounds. Thus, the efficiency improvement with heavy alkali PDT can be attributed to reduced band bending at grain boundaries, which reduces tail states and nonradiative recombination and is caused by accumulation of heavy alkalis at grain boundaries.
关键词： grain boundaries,alkali treatment,recombination,bulk,surface,chalcopyrite solar cells
更新于2025-09-16 10:30:52
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Influence of heavy alkali post deposition treatment on wide gap Cu(In,Ga)Se2
摘要： The effect of Potassium, Rubidium, and Cesium post deposition treatment (PDT) on wide bandgap Cu(In,Ga)Se2 (CIGSe) absorbers has been investigated. The results show that the efficiency of the cells can be improved by the alkali treatment and a higher value of the open-circuit-voltage (VOC) can be achieved. In spite of this improvement, the activation energy (EA) of the treated samples remained smaller than the bandgap (Eg) and VOC(t) transients under red light showed a negative slope. Hence, the wide gap CIGSe devices remain limited by recombination at the interface. However, the VOC(t)-transient of treated and untreated samples with the same Eg show a different slope (d Δ?????? (??)/dt). CIGSe samples treated with heavy alkalis (RbF- and CsF-PDT) illustrate a smaller slope in comparison to no-PDT and KF-PDT samples. In this contribution, we discuss the Voc(t) slope, i.e. d Δ?????? (??)/dt, with reference to the illumination dependent doping density (NA,a) and to a possible Sodium exchange mechanisms.
关键词： alkali treatment,wide bandgap,Ga)Se2,Cu(In,recombination,post deposition treatment,solar cells,open-circuit-voltage
更新于2025-09-09 09:28:46