Characterization of CuInSe₂ thin films by XPS

Abstract

The surface composition of CuIaSe, thin films, made by co-evaporation of the elements, has been shown to be strongly dependent on the bulk composition of the films. This is explained by the presence of a secondary phase, most likely Cu,Se, on the surface of Cu-rich Alms. The fast variation of the surface Concentration is also found for films that, according to the equilibrium pseudobinary phase diagram (Cu,Se-In,Se,), should be singlephase chalcopyrite. An explanation, suggesting the presence of a Cu-rich compound also on the surface of films with a composition in the single phase region, is proposed.Surface atomic concentrations have been shown to be modified in CuIaSe, films by a 4.5 keV Ar' sputter etch Heating in vacuum at the film deposition temperature restores the surface atomic concentrations to an asdeposited condition, with the exception of the selenium concentration. The missing selenium atoms are substituted by oxygen atoms still remaining in the film after sputtering and heating.

Influence of Na and H2O on the surface properties of Cu(In,Ga)Se2 thin films

“…Unless otherwise stated ͑e.g., as introduced͒, all surfaces were prepared in situ by cycles of 1 keV Ar ϩ ion sputtering ͑sample currents of 2A/cm 2 at an incident angle of 45°͒ and subsequent annealing at 550 K. Similar procedures have been reported to lead to nearly stoichiometric surfaces of CIGS thin films 16 and single crystals. 17 In the latter case, structurally modified surface layers were detected only for higher ion energies and annealing temperatures.…”

Selenization of CuInS2 by rapid thermal processing – an alternative approach to induce a band gap grading in chalcopyrite thin-film solar cell absorbers?

“…With higher temperature treatment, the leaking rate of Se vapor from the graphite box increases. 23 The calculated values of the modied Se a*, Cu a* and In a* are shown in Fig 24,30,46 and CISe (1849.55 AE 0.25 eV). 24,30,46 The change in In a* values of the samples as a function of surface [Se]/([S] + [Se]) composition is similar to that observed for the Cu a* values (cf.…”

“…The shadowed areas correspond to a* ranges for related reference compounds reported in literature. 24,30,[46][47][48][49] In any case, samples with a lower Se surface content show Cu-poor, In-rich surface compositions. Theoretical work proposes that the presence of electrically neutral defect pairs is possible in chalcopyrite surfaces of similar compositions due to relatively low formation energies for Cu vacancies.…”

Synchrotron-based spectroscopy for the characterization of surfaces and interfaces in chalcopyrite thin-film solar cells

“…Again, only the sample sputter-coated at 150 1C stands out. The value of the resulting Auger parameter [59], together with those from some of the reference samples described above and values from the literature [58,67,68] are given in Table 1. The increase in the value of the modified Auger parameter a' (E bind [Cu 2p 3/2 ]+E kin [Cu LMM]) for the Cu-rich surface points to the formation of a Cu x (S,Se)-like species or a Cu-rich chalcopyrite phase [65].…”

“…It had been shown earlier that the replacement of the i-ZnO/CdS double layer by a rf-sputtered single layer of Zn 0.85 Mg 0.15 O (120 nm) directly on a CIGSSe-absorber without any surface treatment led to a solar cell efficiency of 12.5% [67][68][69] The relative amount of each absorber element was calculated by fitting the individual photoemission peaks Cu 3p (neglecting the small contribution by an In 4p emission at the same binding energy), In 4d, S 2 s and Se 3 s, with the appropriate Voigt functions (including a linear base line). Note that gallium, although present in the bulk, is not detected on the surface of these samples and was therefore not considered here.…”