Effects of Thermochemical Treatment on CuSbS 2. Photovoltaic Absorber Quality and Solar Cell. Reproducibility

Transcription

1 SUPPORTING INFORMATION Effects of Thermochemical Treatment on CuSbS 2 Photovoltaic Absorber Quality and Solar Cell Reproducibility Francisco Willian de Souza Lucas, [a],[b] Adam W. Welch, [a],[c] Lauryn L. Baranowski, [a],[c] Patricia C. Dippo, [a] Hannes Hempel, [d] Thomas Unold, [d] Rainer Eichberger, [d] Beatrix Blank, [e] Uwe Rau, [e] Lucia H. Mascaro, [b] Andriy Zakutayev* [a] [a] National Renewable Energy Laboratory, Denver West Parkway, Golden, CO 80401, USA, [b] Federal University of Sao Carlos, Road Washington Luiz, km 235, São Carlos, SP , Brazil, [c] Colorado School of Mines, 1500 Illinois Street, Golden, CO 80401, USA, [d] Helmholtz Zentrum Berlin für Materialien und Energie GmbH, Hahn Meitner Platz 1, Berlin, Germany, [e] IEK5-Photovoltaik, Forschungszentrum Juelich GmbH, Wilhelm-Johnen- Straße, Juelich, Germany. * andriy.zakutayev@nrel.gov Tel.: S1

2 Selective chemical etch: The chemical etch based on KOH 0.1 mol L -1 that was developed for removing any possible Sb 2 S 3 impurities after CuSbS 2 film growth (which is under overflux of Sb 2 S 3 ) or thermochemical annealing under Sb 2 S 3 atmosphere. This chemical removal process is selective to the Sb 2 S 3 phase (or to the Sb 2 O 3, which has similar chemistry), as can be seen in Figure S1A, which shows the composition and thickness variation (measured by XRF) of an intentionally Sb 2 S 3 -rich CuSbS 2 (Sb 2 S 3 excess of 15 % atm.) during the KOH 0.1 mol L -1 etch. It can be seen that after total Sb 2 S 3 removal (90 min.), the KOH bath does not affect the remaining CuSbS 2 composition. For films with possibility of small quantity of Sb 2 S 3 excess, as in the case of the CuSbS 2 films presented in this work (the excess is below the XRF s and XRD s detection limits), the etching time needed to remove this impurity is very small. However, even the small amount of Sb 2 S 3 impurities on the surface may increases the recombination at the CuSbS 2 film surface, as can been seen in the PL spectra shown in Figure S1B. It is observed that the PL peak for the TT-11h film without KOH etch is wider and less intense than for the film after KOH treatment, suggesting that this effect may be associated with recombination on surface states. However, more detailed PL studies (currently in progress) are needed to understand this observation in more details. S2

3 A) % Atomic relative Cu Sb Thickness Thickness (µm) B) Cnts. (a.u.) TT-11h Film at 25 C Without With KOH etch Etching time (min) hν / ev Fig. S1. A) Composition and thickness of a Sb 2 S 3 -rich CuSbS 2 film as a function of KOH etching time. B) PL spectra of the TT-11h film with and without KOH etch. Pre-TT TT-5h TT-8h TT-11h ICSD Intensity (a.u. x10 3 ) θ ( ) Fig. S2 XRD patterns in logarithmic scale, Inset shows the change in preferential orientation of the CuSbS 2 films upon annealing in linear scale. The standard XRD pattern used as comparison was the ICSD orthorhombic CuSbS 2. S3

4 Fig. S3 SEM surface images of the A) pre-tt and B) TT-8h, C) TT-11h and D) Step TT-11h CuSbS 2 films. α(x10 4 cm -3 ) Pre-TT TT-5h TT-8h TT-11h (αhν) 2 (cm -2 ev 2 x10 10 ) Photon Energy (ev) Fig S4 Graphs of absorption coefficient (α), in logarithmic scale, and (αhν) 2 [insert] versus photon energy. S4

5 max R (a.u.) τ 1 τ 2 τ 3 w/o CdS (τ 3 =0.7 ns) w CdS (τ 3 =0.4 ns) t pump (ps) Fig. S5 Time-domain optical-pump terahertz-probe spectroscopy results for the TT-11h CuSbS 2 samples, with (w) and without (w/o) the CdS buffer layer. Fig. S6 Cross-section SEM of the A) Pre-TT, B) TT-8h, C) TT-11h D) Step TT-11h devices. S5

6 A) -6.0 Pre-TT TT-8h Step TT-11h B) J (ma cm -2 ) V (Volt) Fig. S7 A) Representative device J-V curves under AM1.5G illumination (100 mw cm 2 ) at 25 and B) Representative fitting of the dark-j-v curves at 25 C using the one-diode model with four adjustable parameters, (Equation 1). Insert: The equivalent circuit used for this fitting. A) J (ma/cm 2 ) K 300 K pre-tt B) J (ma/cm 2 ) Step TT-11h 300 K 130 K V [Volt] V [Volt] Fig. S8 J-V curves as a function of measurement temperature (T= 300, 250, 210,180, 150, 130 K) for the PV devices with (A) pre-tt and (B) Step TT-11h CuSbS 2 absorbers. S6

7 step TT-11h EQE (r.u.) Photon Energy (ev) Fig. S9 External quantum efficiency (EQE) in relative units for Step TT-11h measured by Fourier transform photocurrent spectroscopy. S7