Liquid‐selenium‐enhanced grain growth of nanoparticle precursor layers for CuInSe₂ solar cell absorbers

Abstract

Large-grained CuInSe 2 absorber layers are synthesized using a non-vacuum process based on nanoparticle ink precursors and selenization by rapid thermal processing (RTP). The use of hydroxide-based particles in organic solvents allows for the conversion with elemental selenium without the need to employ explosive and/or toxic H 2 or H 2 Se gasses. Lateral grain sizes up to 4 μm are obtained through a novel RTP route, overcoming the inherently high layer porosity for previous nanoparticle processes. Morphological and elemental characterization at interrupted selenization steps suggests that liquid selenium can play a beneficial role in promoting layer densification and grain growth. Long carrier collection lengths in CuInSe 2 enable notable conversion efficiencies, despite the low minority carrier lifetimes of below 1 ns. Record efficiencies up to 8.73% highlight the potential of low-cost, non-vacuum deposition of chalcopyrite absorber layers with safe and simple precursors and processing routes.

High-Efficiency Nanoparticle Solution-Processed Cu(In,Ga)(S,Se)2Solar Cells

“…This structure is similar to many other reported solutionprocessed devices [7], [12], [13]. However, the recrystallized region dominates with a much smaller nanocrystalline region.…”

Molecular-ink route to 13.0% efficient low-bandgap CuIn(S,Se)2 and 14.7% efficient Cu(In,Ga)(S,Se)2 solar cells

“…H2, H2S, or H2Se) to reduce precursor layers [12][13][14] or toxic KCN etching to remove binary selenides. 15 18 The highest efficiency from a pure solution process to date uses the carbon-free solvent hydrazine to achieve up to 15.2% efficient Cu(In,Ga)(S,Se)2 devices, 19 but the toxic and explosive nature of the solvent may not be suitable for industrial implementation. Gallium-free absorbers from the same process have yielded up to 12.2% efficient devices with only slightly reduced bandgap from 1.16 to 1.15 eV, and 10.6% with a bandgap of 1.08 eV (12.7% and 10.6% using quantum efficiency data).…”

Solution‐Processed Low‐Bandgap CuIn(S,Se)2 Absorbers for High‐Efficiency Single‐Junction and Monolithic Chalcopyrite‐Perovskite Tandem Solar Cells

“…Thin film solar cells based on chalcogenide and perovskite absorbers are particularly promising as they have achieved the highest power conversion efficiencies among thin film solar cells of over 22% -exceeding market-leading polycrystalline silicon (pc-Si) -and can be fabricated by liquid deposition methods due to their high absorption constants. [2][3][4][5] Moreover, both technologies exhibit a wide range of bandgap tunability, which allows for their integration in solution-processed tandem solar cells that can further boost device efficiencies by over 40% and promote the reduction of solar electricity prices to values below those of coal or gas. [6] Tandem solar cells represent an exciting means to increase the power conversion efficiency (PCE) of solar cells by increasing the absorption of photons and reducing thermalization losses of electrons.…”

“…[10] While these results are impressive, the devices typically employ a mechanically-stacked architecture which eases manufacturing but may not be economically solution-processing. [4,5,11,12] Moreover, the bandgap of CIGS can be tuned to values as low as 1.0 eV which is predicted to afford excellent current matching in monolithic tandem devices with the current highest efficiency PSCs with a bandgap of 1.6 eV. [3,13] for the 11.4% efficient bottom cells were thereby obtained from hydrazine solutions, whose high toxicity and flammability may pose hindrances for commercialization.…”