We present a comprehensive study of the thermodynamic and electronic properties of intrinsic point defects in the solar energy conversion materials Cu 2 ZnSnSe 4 and CuInSe 2 based on screened-exchange hybrid density functional theory. A comparison between the defect transition levels for Cu 2 ZnSnSe 4 and CuInSe 2 reveals that in Cu 2 ZnSnSe 4 , the Sn Cu and Sn Zn antisite defects can be recombination centers with defect states close to mid-gap, while the In Cu antisite defect has a shallow defect level in CuInSe 2. The resultant higher Shockley-Read-Hall recombination rate in Cu 2 ZnSnSe 4 reduces the steady-state concentration of minority carriers and quasi Fermi level separation under illumination. This may explain the origin of the low open-circuit voltage values for Cu 2 ZnSnSe 4 solar cells compared to CuInSe 2 solar cells.

We present a comprehensive study of the earth-abundant semiconductor Cu 3 N as a potential solar energy conversion material, using density functional theory and experimental methods. Density functional theory indicates that among the dominant intrinsic point defects, copper vacancies V Cu have shallow defect levels while copper interstitials Cu i behave as deep potential wells in the conduction band which mediate Shockley-Read-Hall recombination. The existence of Cu i defects has been experimentally verified using photothermal deflection spectroscopy. A Cu 3 N/ZnS heterojunction diode with good current-voltage rectification behavior has been demonstrated experimentally, but no photocurrent is generated under illumination. The absence of photocurrent can be explained by a large concentration of Cu i recombination centers capturing electrons in p-type Cu 3 N. 1V) of 14. The large reverse-bias leakage current of 20 mA/cm 2 at-1 V is likely due to pinholes in the Cu 3 N absorber layer giving rise to a low shunt resistance. Under illumination, however, the Cu 3 N/ZnS p-n junction does not generate any photocurrent, suggesting either limitations in carrier transport in the Cu 3 N absorber layer due to defect states or energy barriers blocking carrier transport at the interfaces. From the inset of Fig. 9(a), linear current-voltage characteristics are observed for both Mo and In contacts on Cu 3 N with current levels commensurate with the film resistivity and thickness, confirming that Mo serves as a good ohmic contact for p-type Cu 3 N.

Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. A broad and expanding range of materials can be produced by atomic layer deposition at relatively low temperatures, including both oxides and metals. For many applications of interest, however, it is desirable to grow more tailored and complex materials such as semiconductors with a certain doping, mixed oxides, and metallic alloys. How well such mixed materials can be accomplished with atomic layer deposition requires knowledge of the conditions under which the resulting films will be mixed, solid solutions, or laminated. The growth and lamination of zinc oxide and tin oxide is studied here by means of the extremely surface sensitive technique of low energy ion scattering, combined with bulk composition and thickness determination, and x-ray diffraction. At the low temperatures used for deposition (150 C), there is little evidence for atomic scale mixing even with the smallest possible bilayer period, and instead a morphology with small ZnO inclusions in a SnO x matrix is deduced. Postannealing of such laminates above 400 C however produces a stable surface phase with a 30% increased density. From the surface stoichiometry, this is likely the inverted spinel of zinc stannate, Zn 2 SnO 4 . Annealing to 800 C results in films containing crystalline Zn 2 SnO 4 , or multilayered films of crystalline ZnO, Zn 2 SnO 4 , and SnO 2 phases, depending on the bilayer period.