Impact of Na Doping on the Carrier Transport Path in Polycrystalline Flexible Cu₂ZnSn(S,Se)₄ Solar Cells

Abstract

It is well‐known that the alkali doping of polycrystalline Cu 2 ZnSn(S,Se) 4 (CZTSSe) and Cu(In,Ga)(Se,S) 2 has a beneficial influence on the device performance and there are various hypotheses about the principles of performance improvement. This work clearly explains the effect of Na doping on the fill factor (FF) rather than on all of the solar cell parameters (open‐circuit voltage, FF, and sometimes short circuit current) for overall performance improvement. When doping is optimized, the fabricated device shows sufficient built‐in potential and selects a better carrier transport path by the high potential difference between the intragrains and the grain boundaries. On the other hand, when doping is excessive, the device shows low contact potential difference and FF and selects a worse carrier transport path even though the built‐in potential becomes stronger. The fabricated CZTSSe solar cell on a flexible metal foil optimized with a 25 nm thick NaF doping layer achieves an FF of 62.63%, thereby clearly showing the enhancing effect of Na doping.

Optimizing the Ratio of Sn4+ and Sn2+ in Cu2ZnSn(S,Se)4 Precursor Solution via Air Environment for Highly Efficient Solar Cells

“…When the ratios of Sn 4+ to Sn 2+ was 1:0 and 0:1, the average roughness was 91.46 and 99.26 nm. According to the literature, [ 30,33–37 ] the rough CZTSSe films have a comparatively high number of defects in the heterojunction region, which acts as an interfacial recombination center. The smaller roughness indicates the better film surface quality of absorption layer, which is beneficial for the growth of the much better and more uniform CdS film with the same chemical bath deposition (CBD) process, showing superior heterojunction quality.…”

Improving Ultraviolet Responses in Cu2ZnSn(S,Se)4 Thin-Film Solar Cells Using Quantum Dot-Based Luminescent Down-Shifting Layer

“…The CZTSSe-1 and CZTSSe-4 samples showed CuSe secondary phase peaks at 257 cm −1 [ 26 ], while the other samples showed no secondary peaks in their Raman spectra. All samples showed CZTSe-like peaks at 174, 193, and 228 cm –1 as well as a relatively small CZTS-like peak at 319 cm −1 [ 27 , 28 ]. Therefore, it is further verified again that the Se content is higher than the S content.…”

Perovskite Quantum Dot Solar Cells: An Overview of the Current Advances and Future Perspectives

“…The same behavior is also observed for conventional perovskite thin films [ 166–168 ] and chalcogenide thin films. [ 169–171 ] Poor adhesion of the TCO on these substrates, low barrier properties and chemical stability compared with typical glasses, and the restricted working temperature for the solar cell assembly, principally, are some key reasons that make polymer‐based flexible solar cells generally less efficient than the ones constructed on rigid glasses. [ 166,172 ] Particularly, the PQD technology can contribute to solve this latter problem.…”