Band offset engineering in ZnSnN 2 -based heterojunction for low-cost solar cells

Transcription

1 Band offset engineering in ZnSnN 2 -based heterojunction for low-cost solar cells Kashif Javaid 1,2,3, Weihua Wu 1, Jun Wang 4, Junfeng Fang 1, Hongliang Zhang 1, Junhua Gao 1, Fei Zhuge 1, Lingyan Liang*,1,5 and Hongtao Cao*,1 1 Ningbo Institute of Materials Technology and Engineering (NIMTE), Chinese Academy of Sciences (CAS), Ningbo , People s Republic of China. 2 International School, University of Chinese Academy of Sciences, Beijing , China. 3 Department of Physics, Govt. College University Faisalabad (GCUF), Allama Iqbal Road, Faisalabad, Pakistan. 4 Department of Microelectronic Science and Engineering, Faculty of Science, Ningbo University, Ningbo , China. 5 Key Laboratory of Semiconductor Materials Science, Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, , China. Corresponding author information: * lly@nimte.ac.cn (L. Y. L), Phone/Fax: * h_cao@nimte.ac.cn (H. T. C), Phone/Fax:

2 Figure S1 illustrates the fabrication scheme of P-i-N heterojunction device on ITO glass of dimension 2 2 cm 2. The deposition of each thin film layer was carried out followed by a shadow mask which divided it in 20 devices with effective area of cm 2. Prior to deposit topelectrodes of Ni/Au, some of the P-i-N junction devices were subjected to tube furnace as postfabrication annealing at a temperature of 350 C for 3 hours under N 2 -atmosphere. Figure S1: The schematic illustration of P-N and P-i-N heterostructure photovoltaic devices fabricated on ITO glass. Figure S2 shows that the variation in optical band gap of as-deposited and annealed ZnSnN 2 thin films. The process of heat treatment has significantly reduced the band-tail states in ZnSnN 2 absorber material which causes to increase the optical band gap from 1.66 ev to 1.72 ev, much close to previous reports. 1-2 The inset shows the transmittance spectra for bare ITO, SnO/ITO and for P-i-N heterojunction ZnSnN 2 /Al 2 O 3 /SnO/ITO device. The spectra of SnO window layer (~50 nm) is fairly transparent (more than 85%) for visible light, which enables the practical applicability of SnO as transparent window layer in photovoltaic applications. 3 It S1

3 reveals that that most of visible light is transmitted through this layer and being absorbed in ZnSnN 2 layer. Figure S2: The optical band gaps of as-deposited and annealed ZnSnN 2 thin films and transmittance spectra of bare ITO (as reference), SnO/ITO (window layer) and P-i-N heterostructure device is shown in the inset. Figure S3 demonstrates the rich ternary chemistry with lattice-matched alloy ZnSnN 2, belongs to II-VI-V 2 materials. This recently reported material is very similar III-V materials (e.g., GaN), which has already attracted a great deal of interests in the field of photovoltaics. in fact GaN can be mutated to ZnSnN 2 by replacing two Ga- atoms of GaN with each of Zn and Sn contents, 4-5 as shown in Figure S3. Its thermodynamic stability can be studied from the following relationship; S2

4 Zn(hcp) + Sn(diamond) + N 2 (gas) ZnSnN 2 where Zn is found in close packed-hexagonal (HCP) structure, Sn is in the diamond-structure and N 2 is in gas molecule state. Figure S3: Crystal structure of ZnSnN2 (0001). Table S1: Summary of microstructural and optical properties of as-deposited and annealed ZnSnN 2 thin films synthesized by dc-magnetron sputtering. Sample Grain size (nm) d-spacing (nm) RMS roughness (nm) Band gap (ev) Phase of ZnSnN2 Pristine n-type 350 C 5-15 ~ n-type S3

5 Table S2: Diode parameters derived from J-V measurements performed in dark for all fabricated devices (1-3). Diode parameters in dark Device-1 Device-2 Device-3 Turn on voltage (V) Rectification ratio Ideality factor Series resistance (Ω) Table S3: Solar cell parameters derived from J-V measurements performed under 1-sun spectra for all fabricated devices (1-3). Solar cell parameters under AM-1.5 Device-1 Device-2 Device-3 Open circuit voltage (V) Short circuit current density (ma/cm 2 ) 5.3 m Fill factor Maximum power (mw) Power conversion efficiency (%) S4

6 References (1) Javaid, K.; Yu, J.; Wu, W.; Wang, J.; Zhang, H.; Gao, J.; Zhuge, F.; Liang, L.; Cao, H. Thin Film Solar Cell Based on ZnSnN 2 /SnO Heterojunction. Phys. Status Solidi RRL 2017, (DOI: /pssr ). (2) Qin, R.; Cao, H.; Liang, L.; Xie, Y.; Zhuge, F.; Zhang, H.; Gao, J.; Javaid, K.; Liu, C.; Sun, W. Semiconducting ZnSnN 2 thin films for Si/ZnSnN2 p-n junctions. Appl. Phys. Lett. 2016, 108, (3) Arca, E.; Fioretti, A.; Lany, S.; Tamboli, A. C.; Teeter, G.; Melamed, C.; Pan, J.; Wood, K. N.; Toberer, E.; Zakutayev, A. Band Edge Positions and Their Impact on the Simulated Device Performance of ZnSnN 2 -Based Solar Cells. IEEE J. Photovoltaics 2018, 8, (4) Chen, S.; Narang, P.; Atwater, H. A.; Wang, L.-W. Phase Stability and Defect Physics of a Ternary ZnSnN 2 Semiconductor: First Principles Insights. Adv. Mater. 2014, 26, (5) Martinez, A. D.; Fioretti, A. N.; Toberer, E. S.; Tamboli, A. C. Synthesis, structure, and optoelectronic properties of II-IV-V 2 materials. J. Mater. Chem. A 2017, 5, S5