Cheng-Ying Chen1 2 Naili Saidatin1 2 4 Chih-Yang Huang1 2 4 Bandiyah Sri Aprillia1 2 3 Ruei-San Chen3 Jih-Shang Hwang4 Kuei-Hsien Chen2 1 Li-Chyong Chen1

1, National Taiwan University, Taipei, , Taiwan
2, Institute of Atomic and Molecular Science, Academia Sinica, Taipei, Taiwan, Taiwan
4, National Taiwan Ocean University, Keelung, , Taiwan
3, National Taiwan University of Science and Technology, Taipei, Taiwan, Taiwan

Cu2ZnSn(S,Se)4 (CZTSSe) is one of the earth-abundant/non-toxic alternative compounds for the commercialized metal chalcogenides (i.e., CdTe and Cu(In,Ga)(S,Se)2) thin-film photovoltaics (PVs). To raise the performance of CZTSSe based solar cells, much effort has been applied to improving the quality of absorbers, band alignments/passivation at p-n junction, front and back interfaces/contacts. [1,2,3]
In this work, we demonstrated the enhanced open circuit voltage (Voc) of CZTSSe PVs by introducing an interfacial alkaline earth fluoride (several nm MgF2) between the absorber (i.e., CZTSSe) and the buffer layer (i.e., CdS) after sulfo-selenization processes without post-annealing. In statistical studies (10 cells), the alkaline earth fluoride increases power conversion efficiency from 7.5% to 8.8%, short circuit current density (Jsc) from 30.7 mA/cm2 to 32.6 mA/cm2 and Voc from 440 mV to 470 mV, possibly resulting from the MgF2 induced electric field passivation at grain boundaries. [2]. Finally, a 9.4 % efficient CZTSSe solar cell with Voc of 470 mV, Jsc of 32.96 mA/cm2 and fill factor (FF) of 60.7 % was obtained.
The morphology, elemental composition, and distribution of the absorber layers are being examined by scanning Kelvin probe microscopy measurement, X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF), scanning electron microscopy (SEM), Raman spectroscopy, and nano Auger electron spectroscopy (AES).

[1] V. Tunuguntla, W.C. Chen, P.H. Shih, I. Shown, Y.R. Lin, C.H. Lee, J.S. Hwang, L.C. Chen and K.H. Chen, J. Mater. Chem. A, 2015,3, 15324-15330
[2] Y.R. Lin, V. Tunuguntla, S.Y. Wei, W.C. Chen, D. Wong, C.H. Lai, L.K. Liu, L.C. Chen and K.H. Chen, Nano Energy, 2015, 16, 438
[3] W.C. Chen, C.Y. Chen, V. Tunuguntla, S.H. Lu, C. Su, C.H. Lee, K.H. Chen and L.C. Chen, Nano Energy, 2016, 30, 762-770