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Luminescence detection of the 0.8 eV defect

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Luminescence Detection of the 0.8 eV Defect in Cu(In,Ga)Se 2

Conrad Spindler and Susanne Siebentritt

University of Luxembourg, Laboratory for Photovoltaics

Conclusion Motivation

• photocapacitance measurements reveal defect signature at 800 meV above valence band [1]

• signal appears independent of Ga/(Ga+In) ratio and in ternary compounds CuInSe2/CuGaSe2

• if the signal is caused by defects, we should observe the levels in photoluminescence measurements

• by extending our setup we perform defect

spectroscopy on thin films down to 400 meV

Literature: Theory Photoluminescence 10K

• calculations predict the charge transition CuIn(-1/-2) at 0.6 - 0.8 eV above the VBM in CuInSe2

• Pohl et. al. calculated CuGa(-1/-2) at the same level

• under most preparation conditions Ef close to VB:

 no direct formation of CuIII-1

 photoexcitation needed to charge CuIII-1

Experimental details

GaAs-substrate luminescence?

[1] Heath et. al., Appl. Phys. Lett. 80 (24), 2002

[2] Krysztopa et. al., J. Phys. D: Appl. Phys. 45 (335101), 2012 [3] Mansfield et. Al., IEEE 42nd PVSC, 2015

[4] Yee et. al., Phys. Rev. B 92 (195201), 2015

[5] Malitckaya et. al., Adv. Electron. Mater. 1600353, 2017 [6] Pohl et. al., Phys. Rev. B 87 (245203), 2013

• transition at 0.7 eV for 10K, at 0.8 eV for 300K

• deep defect level remains constant for varying GGI

• defect level not observed in Cu-poor compositions

• defect level attributed to CuIII(-1/-2) antisite

• possible reason for loss of VOC in Cu-rich solar cells

• samples grown by MOVPE on SI-(100)-GaAs

• InAs-detector, range down to 0.4 eV (3100nm)

• InGaAs-array, range down to 0.77 eV (1610nm)

• GaAs has known EL2 defect (AsGa antisite) with optical transitions around 0.7 eV

• PL signals with direct susbtrate-illumination have lower intensities than for CuInSe2/GaAs

 deep defect transitions not correlated to substrate

• transition at 0.68 eV most likely DA-transition into dominant shallow acceptor at 100 meV

• deep level remains constant when adding Indium

 defect level exists around 0.7 - 0.8 eV

Deep defect observable at 300K?

What about lower Cu-contents?

Acknowledgements

Michele Melchiorre, Germain Rey

• defect transition at 0.8 eV for room temperature

• free-to-bound transition  defect level at 0.8 eV

• observed in Cu-rich CuInSe2 and Cu(InGa)Se2

Literature: Experiment

0.8eV

• defect just observed

in experiments with excitation

• 0.8 eV defect observed by photocapacitance [1]

• independent of Ga/(Ga+In) ratio in Cu(In,Ga)Se2

• PICTS shows defect response around 0.8 eV in

epitaxial/polycrystalline CuInSe2 and CuGaSe2 [2]

• recently PL transition shown at 0.8 eV [3]

CuInSe2

A

CuIn0.7Ga0.3Se

B

CuIn0.5Ga0.5Se

C

CuIn0.2Ga0.8Se2

D

CuGaSe2

E

GGI 0 0.27 0.46 0.8 1

CGI 1.25 0.99 1.29 1.13 1.18

[1] [2]

[3]

• 0.8 eV defect peak not observed in state-of-the-art absorber with GGI approx. 0.3 and CGI approx. 0.9

• Sample B with CGI 0.99

shows smallest defect signal

• 0.8 eV signal decreases with respect to band-band

transition for lower Cu-content

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