CuSCN as the Back Contact for Efficient ZMO/CdTe Solar Cells

Abstract

The replacement of traditional CdS with zinc magnesium oxide (ZMO) has been demonstrated as being helpful to boost power conversion efficiency of cadmium telluride (CdTe) solar cells to over 18%, due to the reduced interface recombination and parasitic light absorption by the buffer layer. However, due to the atmosphere sensitivity of ZMO film, the post treatments of ZMO/CdTe stacks, including CdCl2 treatment, back contact deposition, etc., which are critical for high-performance CdTe solar cells became crucial challenges. To realize the full potential of the ZMO buffer layer, plenty of investigations need to be accomplished. Here, copper thiocyanate (CuSCN) is demonstrated to be a suitable back-contact material with multi-advantages for ZMO/CdTe solar cells. Particularly, ammonium hydroxide as the solvent for CuSCN deposition shows no detrimental impact on the ZMO layer during the post heat treatment. The post annealing temperature as well as the thickness of CuSCN films are investigated. Finally, a champion power conversion efficiency of 16.7% is achieved with an open-circuit voltage of 0.857 V, a short-circuit current density of 26.2 mA/cm2, and a fill factor of 74.0%.

20%-efficient polycrystalline Cd(Se,Te) thin-film solar cells with compositional gradient near the front junction

“…4a–d . Mature Cu doping was used for both the control and target devices 44 , 45 . It is seen that the control devices show V OC s lower than 0.840 V, similar to that of Cd(Se,Te) solar cells without ZMO buffer layer previously reported by researchers 36 .…”

“…CdTe absorber (3.5 µm) was then deposited by close-space sublimation (CSS) at the source and substrate temperatures of 660 and 590 °C, respectively, at 10 Torr, followed by a wet cadmium chloride (CdCl 2 ) treatment at 400 °C for 50 min in dry air. CuSCN (~50 nm) was deposited by the spin-coating method using 2 mg ml −1 solution in 30 wt% ammonium hydroxide with 2000 rpm spin speed for 30 s. Then, a rapid thermal annealing process at 180 °C was used to facilitate the Cu diffusion according to our previous report 44 , 45 . After the rapid thermal annealing treatment, an Au layer (40 nm) was evaporated on the back surface with an individual device area of 0.08 cm 2 .…”

Effects of Cu Precursor on the Performance of Efficient CdTe Solar Cells

“…In this regard, various Cu precursors have been used as the Cu source to fabricate CdTe thin-film solar cells. In general, two kinds of Cu precursors, including metallic Cu, covalent Cu compounds, e.g., Cu x Te, Cu doped ZnTe, and ionic Cu compounds, e.g., CuSCN, , cuprous chloride (CuCl), ,, and copper chloride (CuCl 2 ). , Among them, CuCl and CuCl 2 have attracted extensive attention due to its outstanding performance. Recently, CuCl 2 was incorporated in the CdTe absorber as the Cu precursor to eliminate the diffusion of Cu into the front junction, achieving a maximum PCE of ∼16% .…”

Water-Assisted Lift-Off Process for Flexible CdTe Solar Cells

“…SCAPS simulation was conducted to investigate the effect of the increased conductivity of the CdS film on device performances. The input parameters for SCAPS simulation are tabulated in Table S1. , When the work function decreases by 0.3 eV, the carrier density of CdS increases from 1 × 10 14 to 1 × 10 18 cm –3 . The simulated band alignments show that the device with 0.3 eV lower work function introduces an additional downward band bending in the CdTe absorber adjacent to the CdS front interface (Figure g), which can more efficiently expel the holes from the interface and reduce the nonradiative recombination therein.…”