Verification of minority carrier traps in Cu(In,Ga)Se2 and Cu2ZnSnSe4 by means of time-resolved photoluminescence

Maiberg, Matthias; Hölscher, Torsten; Jarzembowski, Enrico; Hartnauer, Stefan; Zahedi‐Azad, Setareh; Fränzel, Wolfgang; Scheer, Roland

doi:10.1016/j.tsf.2017.02.002

Cited by 15 publications

(9 citation statements)

References 32 publications

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“…Taking into account the concomitant increase of the band-edge emission, observed mainly at the higher deposition temperature, we tentatively assign τ short to non-radiative recombination associated with trapping of carriers at the deep levels while τ long is associated with the dynamics of the band-to-band transition. Trapping times of the order of few ns and band-to-band recombination of the order of tens to hundreds of ns such as those observed in our films, have been routinely reported in the literature for evaporated CIGS films [13,15,17,19] so such assignment appears reasonable. It is noted that within the low excitation level range of 1 to 25 μW employed in our TCSPC experiments, no influence of the excitation fluence was observed in PL dynamics, which suggests that defect saturation effects by carriers is absent [13,15].…”

Section: Resultssupporting

confidence: 77%

Luminescence properties of pulsed laser deposited CuIn_xGa_1−xSe₂ films

et al. 2020

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Pulsed laser deposition (PLD) of CuIn 1−x Ga x Se 2 (CIGS) provides a low cost, single-step process via which stoichiometric, high quality thin films for light harvesting applications can be produced. Little is known about the optical properties of PLD-deposited CIGS and how they compare with the respected properties of the well-studied evaporated or sputtered CIGS films. We report herein a systematic spectroscopic investigation, probing the influence of PLD deposition temperature on the energetics and dynamics of emission from CuIn 0.7 Ga 0.3 Se 2 films. Variable-temperature steady-state and time-resolved photoluminescence in combination with Gaussian lineshape analysis allow us to unravel the contribution and nature of three main radiative channels, with the high energy one associated with electronic and two lower energy ones with defect levels. The analysis show that the band-edge luminescence grows at the expense of defect emission as PLD temperature increases in the 300°C-500°C range. This is further supported by: (i) The dramatic increase of the band-edge recombination lifetime from 30 to 180 ns, (ii) The quenching in the carrier trapping rate from 0.25 ns −1 to 0.09 ns −1 as growth temperature increases. The results correlate well with structural and electrical characterization studies reported previously on PLD-grown CIGS and rationally interpret the improvement in their optoelectronic properties as PLD deposition temperature increases .

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Section: Resultssupporting

confidence: 77%

Luminescence properties of pulsed laser deposited CuIn_xGa_1−xSe₂ films

et al. 2020

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“…Consequently, the difference of Δμ PL and Δμ TRPL can be explained by small deviations of the input parameters τ TRPL and p 0 . In particular, major deviations of τ TRPL are not expected as for instance reported for CIGS absorbers, which are influenced by trapping [6,35], where the measured decay time is in the order of 100 ns, while the simulation of the decay curve yielded only 1-20 ns.…”

Section: δQ þ Xmentioning

confidence: 57%

Time-resolved photoluminescence on double graded Cu(In,Ga)Se₂ – Impact of front surface recombination and its temperature dependence

Weiss

Carron

Wolter

et al. 2019

Science and Technology of Advanced Materials

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Time-resolved photoluminescence (TRPL) is applied to determine an effective lifetime of minority charge carriers in semiconductors. Such effective lifetimes include recombination channels in the bulk as well as at the surfaces and interfaces of the device. In the case of Cu(In,Ga)Se 2 absorbers used for solar cell applications, trapping of minority carriers has also been reported to impact the effective minority carrier lifetime. Trapping can be indicated by an increased temperature dependence of the experimentally determined photoluminescence decay time when compared to the temperature dependence of Shockley-Read-Hall (SRH) recombination alone and can lead to an overestimation of the minority carrier lifetime. Here, it is shown by technology computer-aided design (TCAD) simulations and by experiment that the intentional double-graded bandgap profile of high efficiency Cu(In,Ga)Se 2 absorbers causes a temperature dependence of the PL decay time similar to trapping in case of a recombinative front surface. It is demonstrated that a passivated front surface results in a temperature dependence of the decay time that can be explained without minority carrier trapping and thus enables the assessment of the absorber quality by means of the minority carrier lifetime. Comparison with the absolute PL yield and the quasi-Fermi-level splitting (QFLS) corroborate the conclusion that the measured decay time corresponds to the bulk minority carrier lifetime of 250 ns for the double-graded CIGS absorber under investigation. ARTICLE HISTORY

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“…Recent work using high-resolution intensity-and temperature-dependent TRPL has shown that the characteristic PL decay times for kesterites can commonly be attributed to trapping/de-trapping processes in the material rather than the minority carrier lifetime [4,92]. Trapping is also observed in TRTS measurements [88,93].…”

Section: Measuring a Sub-picosecond Lifetime In Cztssementioning

confidence: 99%

“…However, these cases validate the sub-nanosecond lifetime conclusion for kesterites and alternative high time-resolution measurement techniques are needed such as TRTS. The effect of trapping in kesterite thin films can be mitigated in measurements which probe the excess carrier decay through saturation of trap states at elevated excitation intensities or elevated temperatures during measurement [92,99], however high time-resolution measurement techniques would still be needed to extract τ for kesterites due to fast recombination rates.…”

Section: Measuring a Sub-picosecond Lifetime In Cztssementioning

confidence: 99%

The electrical and optical properties of kesterites

et al. 2019

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Kesterite Cu 2 ZnSn(S x Se 1-x ) 4 (CZTSSe) semiconductor materials have been extensively studied over the past decade, however despite significant efforts, the open circuit voltage remains below 60% of the theoretical maximum. Understanding the optical and electrical properties is critical to explaining and solving the voltage deficit. This review aims to summarize the present knowledge of optical and electrical properties of kesterites and specifically focuses on experimental data of intrinsic defects, charge carrier density and transport, and minority carrier lifetime and related rate-limiting recombination mechanisms. It concludes with suggestions for further investigation of the electrical and optical properties of kesterite materials. of the (001) cationic planes are randomly occupied by Cu and Zn atoms [6,7]. While theoretical calculations by Chen et al [8] find the lowest formation energy for the kesterite crystal structure, cation disorder is present in CZTSSe due to the low energy difference between the stannite-and kesterite-related structures. It has been suggested that the Cu-Zn disorder in Cu 2 ZnSnS 4 (CZTS) follows a second order phase transition with a critical temperature of ∼260°C for CZTS, which was first observed and introduced to describe the modifications in the Raman spectra of CZTS annealed at different temperatures [9]. A similar phenomenon has also been found in Cu 2 ZnSnSe 4 (CZTSe), with a critical temperature of 200°C [10], where the measured increase in band gap is explained by thermally induced ordering of Cu and Zn cations. While the remarkable effect of the orderdisorder transition on the band gap and vibrational spectra is explained by Vineyard's theory [11], the disorder parameter itself is not experimentally determined in the probed samples. A recent direct comparison between resonant x-ray diffraction and photoluminescence (PL) data in CZTSe has confirmed a relationship between the Cu-Zn disorder and the band gap modification [12]. A change in the order parameter from 0 to 0.7 leads to a OPEN ACCESS RECEIVED significant increase in the band gap on the order of ∼0.11 eV and ∼0.20 eV for CZTSe and CZTS, respectively [10,13].The absorption coefficient for CZTS and CZTSe is about ∼2-3 × 10 4 cm −1 at 1.6 eV and at 1.1 eV, respectively, as determined by the normal reflectance and transmittance [2, 13] spectroscopic ellipsometry (SE) [14-16] and external quantum efficiency [17] methods. In the recent review by Choi et al [18] the main theoretical and experimental results on the energy band structure and SE data were discussed and summarized. Recently, Zamulko et al [19] re-examined first principle theory at different levels in order to improve the description of the electronic structure and optical properties of CZTSSe. Nishiwaki et al [20] performed density functional calculation to study absorption band tail of the kesterites. In particular, a theoretical estimate for the tail energy of ∼30 meV for both CZTS and CZTSe was obtained. It was suggested that quite large Urbach energi...

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Verification of minority carrier traps in Cu(In,Ga)Se2 and Cu2ZnSnSe4 by means of time-resolved photoluminescence

Cited by 15 publications

References 32 publications

Luminescence properties of pulsed laser deposited CuIn_xGa_1−xSe₂ films

Luminescence properties of pulsed laser deposited CuIn_xGa_1−xSe₂ films

Time-resolved photoluminescence on double graded Cu(In,Ga)Se₂ – Impact of front surface recombination and its temperature dependence

The electrical and optical properties of kesterites

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Verification of minority carrier traps in Cu(In,Ga)Se2 and Cu2ZnSnSe4 by means of time-resolved photoluminescence

Cited by 15 publications

References 32 publications

Luminescence properties of pulsed laser deposited CuInxGa1−xSe2 films

Luminescence properties of pulsed laser deposited CuInxGa1−xSe2 films

Time-resolved photoluminescence on double graded Cu(In,Ga)Se2 – Impact of front surface recombination and its temperature dependence

The electrical and optical properties of kesterites

Contact Info

Product

Resources

About

Luminescence properties of pulsed laser deposited CuIn_xGa_1−xSe₂ films

Luminescence properties of pulsed laser deposited CuIn_xGa_1−xSe₂ films

Time-resolved photoluminescence on double graded Cu(In,Ga)Se₂ – Impact of front surface recombination and its temperature dependence