Hydrogen-doped In2O3 for silicon heterojunction solar cells: Identification of a critical threshold for water content and rf sputtering power

• Published in: Solar energy materials and solar cells 2021-01, Vol.220, p.110844, Article 110844
• Main Authors: Addonizio, M.L., Spadoni, A., Antonaia, A., Usatii, I., Bobeico, E.
• Format: Article
• Language: English
• Subjects: Annealing; Carrier mobility; Chemical etching; Circuits; Crystal structure; Crystallinity; Crystallites; Crystals; Domains; Etching; Fabrication; Gas mixtures; Heterojunctions; Hydrogen doped indium oxide; Indium; Indium oxides; Indium tin oxides; Magnetron sputtering; Mobility; Moisture content; Optical properties; Photovoltaic cells; Process parameters; Radio frequency; Short circuit currents; Short-circuit current; Silicon; Silicon heterojunction solar cells; Solar cells; Sputtering process; Thin-film; Transparent conductive oxides; Water content; Water vapor
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2020.110844

Hydrogen-doped indium oxide (IO:H) layers with very high carrier mobility have been developed by two-step fabrication procedure. In the first step IO:H films were deposited by radio frequency (RF) magnetron sputtering from In2O3 target in Ar/water vapour gas mixtures. Different sputtering powers and partial pressures of H2O (pH2O) have been explored and effects induced by changes of these process parameters on final film structure and on electro-optical properties have been investigated. In the second step a post-deposition annealing under vacuum were performed. During this treatment a complete and complex amorphous-crystalline transition occurred. Growth of large crystalline domains give rise to IO:H films with excellent carrier mobility values, up to 138 cm2/Vs. For each sputtering power used, the pH2O range has been identified which allows to obtain the highest carrier mobility value for IOH post-annealed films. Growth of large crystallites occurred in IO:H annealed films and, at this purpose, a selective chemical etching method has been developed to give better evidence for the polycrystalline grains. IO:H films appeared formed by fairly large crystalline domains with presence of sub-grains. Silicon heterojunction cells fabricated by using IO:H layers as front electrode, compared with those obtained from a conventional ITO showed improved short-circuit current density and the resulting conversion efficiency. [Display omitted] •IO:H layers have been produced by two step fabrication procedure: RF sputtering process and post-deposition annealing.•The effect of different sputtering powers on the film properties has been investigated.•The carrier mobility of post-annealed IO:H films is highly influenced by the water partial pressure in the sputtering gas.•For an optimized annealing the growth of large crystalline domains occurred giving IO:H films with high mobility up to 138 cm2/Vs.•Silicon heterojunction devices with best performance were obtained when IO:H layers was deposited using a water amount as low as possible.