Ultra-thin Cu2ZnSnS4 solar cell by pulsed laser deposition

Abstract

We report on the fabrication of a 5.2% efficiency Cu 2 ZnSnS 4 (CZTS) solar cell made by pulsed laser deposition (PLD) featuring an ultra-thin absorber layer (less than 450 nm). Solutions to the issues of reproducibility and micro-particulate ejection often encountered with PLD are proposed. At the optimal laser fluence, amorphous CZTS precursors with optimal stoichiometry for solar cells are deposited from a single target. Such precursors do not result in detectable segregation of secondary phases after the subsequent annealing step. In the analysis of the solar cell device, we focus on the effects of the finite thickness of the absorber layer. Depletion region width, carrier diffusion length, and optical losses due to incomplete light absorption and back contact reflection are quantified. We conclude that material-and junction quality is comparable to that of thicker state-of-the-art CZTS devices, even though the efficiency is lower due to optical losses.

Physical routes for the synthesis of kesterite

“…A composite target with the overall stoichiometric composition Cu 2 ZnSnS 4 or Cu 2 ZnSnO 4 is struck by a KrF excimer laser beam. After the deposition, the films were annealed in a graphite box with a S overpressure at a temperature ranging from 550 • C to 600 • C. Using this two-step technique, a first efficiency record of 5.2% was obtained by Cazzaniga et al in 2017 [25] and subsequent cells were completed by Gansukh et al from DTU [27]. Using PLD, one important deposition parameter turns out to be the laser energy per unit area [J cm −2 ] on the composite target.…”

“…This was the case not only for films produced from composite targets, but also for single-phase CZTS targets. For oxide targets, CZTO, it was necessary to apply a target with less copper than the standard composition [25,90].…”

Study and optimization of alternative MBE‐deposited metallic precursors for highly efficient kesterite CZTSe:Ge solar cells

“…Apart from that, kesterite has several advantageous properties to be a very suitable material for photovoltaic applications: kesterite has p‐type conductivity naturally due to intrinsic point defects; it is direct band gap semiconductor with a high absorption coefficient (~10 4 cm −1 ); its band gap can be easily tuned with the ratio S/Se, from 1.0 eV, for the pure selenium Cu 2 ZnSnSe 4 (CZTSe) compound, to 1.5 eV, for the pure sulfur Cu 2 ZnSnS 4 (CZTS); and it is highly compatible with CIGS technology, sharing several processing steps and techniques. Furthermore, the fact that kesterite absorbers can be synthesized with a large variety of techniques is another advantage to consider, especially for future industrial perspectives …”

“…Regarding the deposition techniques, these are usually classified as vacuum (mostly physical vapor deposition [PVD]‐based) and nonvacuum techniques. Vacuum‐based methods include coevaporation, thermal evaporation, e‐beam evaporation, sputtering, or pulsed laser deposition (PLD), among the most widely used. While nonvacuum techniques include solution processing via spin‐coating/dip‐coating/doctor‐blade‐coating/spray/ink‐jet printing of the precursor, or electrochemical deposition …”

“…Furthermore, the fact that kesterite absorbers can be synthesized with a large variety of techniques is another advantage to consider, especially for future industrial perspectives. [8][9][10][11][12][13][14][15][16][17][18] Regarding the deposition techniques, these are usually classified as vacuum (mostly physical vapor deposition [PVD]-based) and nonvacuum techniques.…”