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Suppression of surface recombination in CuInSe_2 (CIS) thin films via Trioctylphosphine Sulfide (TOP:S) surface passivation

Luo, Shi and Eisler, Carissa and Wong, Tsun-Hsin and Xiao, Hai and Lin, Chuan-En and Wu, Tsung-Ta and Shen, Chang-Hong and Shieh, Jia-Min and Tsai, Chuang-Chuang and Liu, Chee-Wee and Atwater, Harry A. and Goddard, William A., III and Lee, Jiun-Haw and Greer, Julia R. (2016) Suppression of surface recombination in CuInSe_2 (CIS) thin films via Trioctylphosphine Sulfide (TOP:S) surface passivation. Acta Materialia, 106 . pp. 171-181. ISSN 1359-6454. doi:10.1016/j.actamat.2016.01.021.

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CuInSe_2 (CIS) solar cells are promising candidates for thin film photovoltaic applications, one key limitation in their performance is surface recombination in these thin films. We demonstrate that passivating CIS films with Trioctylphosphine Sulfide (TOP:S) solution increases photoluminescence (PL) intensity by a factor of ∼30, which suggests that this passivation significantly reduces surface recombination. X-ray photoelectron spectroscopy (XPS) reveals that TOP:S forms both –S and –P bonds on the CIS film surface, which leads to a ∼4-fold increase in the surface Na peak intensity. This value is significantly higher than what would be expected from high temperature annealing alone, which has been linked to improvements in surface morphology and device efficiency in CIGS solar cells. We use Energy-Dispersive X-ray Spectroscopy (EDS) to measure the solid-state transport of Na within CIS films with and without passivation. EDS spectra on CIS film cross-sections reveals a saddle-shaped Na profile in the as-fabricated films and a concentration gradient towards the film surface in the passivated films, with 20% higher surface Na content compared with the unpassivated films. We employ Hybrid (B3PW91) Density Functional Theory (DFT) to gain insight into energetics of Na defects, which demonstrate a driving force for Na diffusion from bulk towards the surface. DFT Calculations with TOP:S-like molecules on the same surfaces reveal a ∼ 1eV lower formation energy for the Na_(Cu) defect. The experiments and computations in this work suggest that TOP:S passivation promotes Na diffusion towards CIS film surfaces and stabilizes surface Na defects, which leads to the observed substantial decrease in surface recombination.

Item Type:Article
Related URLs:
URLURL TypeDescription
Eisler, Carissa0000-0002-5755-5280
Xiao, Hai0000-0001-9399-1584
Atwater, Harry A.0000-0001-9435-0201
Goddard, William A., III0000-0003-0097-5716
Greer, Julia R.0000-0002-9675-1508
Additional Information:© 2016 Acta Materialia Inc. Published by Elsevier Ltd. Received 16 December 2015; Accepted 8 January 2016. The authors gratefully acknowledge the financial support of the National Science Council of Taiwan, R.O.C. through its grant no. NSC 101-3113-P-008-001. In addition HX and WAG received partial support from the US NSF.
Funding AgencyGrant Number
National Science Council (Taipei)101-3113-P-008-001
Subject Keywords:CuInSe2 (CIS) solar cells; Thin film passivation; Na diffusion; DFT calculations; STEM-EDS
Record Number:CaltechAUTHORS:20160125-140843363
Persistent URL:
Official Citation:Shi Luo, Carissa Eisler, Tsun-Hsin Wong, Hai Xiao, Chuan-En Lin, Tsung-Ta Wu, Chang-Hong Shen, Jia-Min Shieh, Chuang-Chuang Tsai, Chee-Wee Liu, Harry A. Atwater, William A. Goddard III, Jiun-Haw Lee, Julia R. Greer, Suppression of surface recombination in CuInSe2 (CIS) thin films via Trioctylphosphine Sulfide (TOP:S) surface passivation, Acta Materialia, Volume 106, March 2016, Pages 171-181, ISSN 1359-6454, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:63936
Deposited By: Tony Diaz
Deposited On:25 Jan 2016 22:16
Last Modified:10 Nov 2021 23:23

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