Spray Pyrolysis of CuIn(S,Se)₂ Solar Cells with 5.9% Efficiency: A Method to Prevent Mo Oxidation in Ambient Atmosphere

Abstract

Direct spray pyrolysis to form CuInS2 (CIS) on molybdenum substrate in ambient environment has been a challenge because of the ease of Mo oxidation at low temperatures. MoO2 formation affects the wettability of precursor solution during spray pyrolysis, which degrades the uniformity of CIS film and acts as a resistive layer for carrier transport. In this paper, Mo oxidation was prevented by using excess sulfur in the precursor solution under a gradual heating and spray process. A thin precursor layer was initially deposited as a barrier layer to prevent oxygen adsorption on Mo surface before the temperature was increased further to form polycrystalline CuInS2. The CuIn(S,Se)2 (CISSe) device fabricated from selenization of the spray-pyrolyzed CIS film exhibited a power conversion efficiency (PCE) of 5.9%. The simple spray method proposed here can be used to deposit a variety of Cu-based chalcopyrite precursor to produce high-quality thin film solar cells.

Cu(In,Ga)(S,Se)2 Thin Film Solar Cell with 10.7% Conversion Efficiency Obtained by Selenization of the Na-Doped Spray-Pyrolyzed Sulfide Precursor Film

“…Most of the reports on the spray pyrolysis-based chalcopyrite devices with appreciable conversion efficiencies involved spray pyrolysis of pure sulfide CuInS 2 or Cu(In,Ga)S 2 precursor film followed by sulfurization or selenization to produce their crystalline compounds or mixed sulfide-selenide compounds. 11,12 It is also possible to fabricate pure selenide CuInSe 2 or Cu(In,Ga)-Se 2 by spray pyrolysis. 13,14 However, for practical application, this approach is often avoided due to the toxicity of the volatile selenium source.…”

Assessing the Band Structure of CuInS2 Nanocrystals and Their Bonding with the Capping Ligand

“…7 The fabrication of efficient CIS solar cells currently requires high temperatures and vacuum methods in a toxic environment, all of which are preventing CIS solar cells from becoming commercially viable. 7,[9][10][11][12][13][14][15][16] Recently, our group has synthesized CIS nanocrystals (NCs) using a one-pot solvothermal method that avoids high-cost and dangerous techniques. [16][17][18] The NCs have been previously characterized photoelectrochemically and structurally.…”

“…Copper-rich CIS has proven to achieve a higher overall quality than indium-rich CIS; 9, 14,19 however, other synthetic methods of copper-rich CIS typically need to be etched by KCN to remove CuS for a high efficiency. 10,[19][20] There has been research on how variations in the composition at different depths affects the band gap due to a secondary CuS phase, 10,[19][20] but it was limited to the effect of etching the CIS surface.…”

Photophysical investigation of charge recombination in CdS/ZnO layers of CuIn(S,Se)2 solar cell

“…14 Although the absorption of CISSe below 450 nm is considerably higher, the external quantum efficiency (EQE) of these devices is found to be lower at these wavelengths. 11 The as-sprayed CIS lm was selenized at 500-550 C for 10 min to form CISSe. 18 Contribution of the photoelectrons generated in the buffer layers to the efficiency of the device is destructive.…”