Characterization of defects in 9.7% efficient Cu2ZnSnSe4-CdS-ZnO solar cells

Abstract

We have fabricated Cu2ZnSnSe4-CdS-ZnO solar cells with a total area efficiency of 9.7%. The absorber layer was fabricated by selenization of sputtered Cu10Sn90, Zn, and Cu multilayers. A large ideality factor of the order of 3 is observed in both illuminated and dark IV-curves, which seems to point in the direction of complex recombination mechanisms such as recombination through fluctuating potentials in the conduction and valence bands of the solar cell structure. A potential barrier of about 135 meV in the device seems to be responsible for an exponential increase of the series resistance at low temperatures, but at room temperature, the effect of this barrier remains relatively small. The free carrier density in the absorber is of the order of 1015 cm−3 and does not vary much as the temperature is decreased.

Different Bandgaps in Cu$_2$ ZnSnSe$_4$: A High Temperature Coevaporation Study

“…In this case, a value of 0.94 ± 0.01 eV can be found. Both values are much lower than the current record device by Brammertz et al, who measured a bandgap of roughly 1.0 eV [7]. As expected, the linear extrapolation of the QE yields smaller values than the inflection point determination.…”

“…1(c) exhibits a high J SC value; however, the voltage is slightly reduced. Solar cell B can be considered as a compromise between the devices A and C. The measured fill factors are comparable with the current record devices [7]. First, we discuss the differences between the devices A and B fabricated with the same type of process.…”

“…The best performing coevaporated samples are currently produced at NREL, and the current record device is 9.15% [6]. The bandgap of CZTSe, as reported by Brammertz et al, is roughly 1.0 eV [7]; it has been deduced from the QE and from room temperature photoluminescence (RT-PL) measurements. Repins et al [6] reported a slightly lower bandgap of 0.96 eV as deduced from RT-PL.…”

Spectroscopic ellipsometry study of Cu2ZnSnSe4 bulk crystals

“…1,2 In spite of this promising value, there are still some unsolved problems related to the single phase growth and its characterization due to the presence of undesired secondary phases of ternary and/or binary compounds [3][4][5][6] and there are only few reports in the literature with experimental information on the fundamental properties of these materials. The investigation of the kesterites optical properties and, in particular, their optical constants, is of great interest for both fundamental and application reasons.…”

Formation of nanometer-sized Cu-Sn-Se particles in Cu2ZnSnSe4 thin-films and their effect on solar cell efficiency

“…The compound semiconductors Cu 2 ZnSn(S,Se) 4 (CZTS(e)) have recently attracted a great deal of attention as absorber materials for thin-film solar cells [1e4]. As a result of intensive research worldwide, CZTS(e) based solar cells have already achieved 12.6% efficiency [2].…”