ELECTRO DEPOSITION OF CUPROUS OXIDE FOR THIN FILM SOLAR CELL APPLICATIONS

Des couches semi-conductrices d’oxyde de cuivre de type p et de type n pour des applications photovoltaiques ont ete fabriquees par voie electrochimique avec des approches nouvelles. Les couches minces ont ete electro-deposees par polarisation cathodique sur une feuille de cuivre et des substrats d'oxyde d'indium-etain (ou oxyde d'indium dope a l'etain (ITO)). Les conditions optimales de depot (composition, pH et temperature de l’electrolyte, domaine de potentiel a appliquer) des couches sous forme de films minces ont ete identifiee, En particulier les conditions qui permettent d’avoir des couches de type n ont ete bien identifiee pour la premiere fois. La configuration d’une pile photo-electrochimique a ete utilisee pour caracteriser la reponse spectrale des couches. Il a ete montre que les couches p delivre un photo-courant dans le domaine cathodique et les couches n dans le domaine de potentiel anodique. Les mesures des resistivites electriques des couches electro chimiquement deposees de Cu2O, de type p et n, ont montre que la resistivite du Cu2O de type p varie de 3.2×105 a 2.0×108 Ω. cm selon les conditions de depot telles le pH de la solution, le potentiel de depot et la temperature. L'influence de plusieurs parametres d'electrodeposition de couches de Cu2O de type, tels que le potentiel applique, le pH et la temperature du bain, sur la composition chimique, le degre de cristallinite, la taille des grains et l'orientation a ete systematiquement etudiee en utilisant la diffraction des rayons X et la microscopie electronique a balayage. Selon le potentiel d’electrodeposition, deux morphologies differentes de surface avec des orientations cristallines preferentielles variees ont ete obtenues pour des temperatures de l’electrolyte de depot de 30 °C et un pH de 9.Pour la meme temperature, les couches de Cu2O de type p, hautement cristallines, se trouvent sont obtenues a pH de 12, ce qui indique que la cristallinite depend du pH du bain. Aussi, il a ete montre que la morphologie des couches de Cu2O etait modifiable en variant le potentiel et la duree de deposition, ainsi que la temperature de la solution. Les conditions d’electrodeposition de Cu2O de type n ont ete identifies de maniere systematique la premiere fois. L’electrolyte de deposition est a base de 0,01 M d’acetate de cuivre et 0,1 M d’acetate de sodium: a un pH compris entre 4 et 6.3, un potentiel compris entre -0,25 V vs Ag/AgCl et une temperature de 60oC. La temperature optimum de recuit des couches n est de 120-150oC pour des durees de 30 a 120 minutes. La resistivite des films de type n varie entre 5x103 et pH 4 a 5x104 a pH 6.4. Nous avons montre pour la premiere fois que le barbotage de l’azote dans la cellule d’electrodeposition des couches de type n ameliore maniere significative leur reponse spectrale. Un procede d’electrodeposition en deux etapes a ete mis en œuvre pour fabriquer la l’homo jonction p-n de l’oxyde oxyde cuivreux sur le substrat l'oxyde d'indium-etain (ITO) qui a ete utilise comme un oxyde conducteur transparent. La performance photovoltaique d'une cellule solaire a homo-jonction p-n de Cu2O a ete determinee. Le courant en court-circuit et la tension de circuit ouvert ont ete respectivement determines a 235 μA/cm2 et 0,35 Volt. Le facteur de remplissage (FF) et le rendement de conversion de la lumiere en electricite des cellules ont ete respectivement evalues a 0,305 et 0,082%. ---------- p and n type copper oxide semiconductor layers were fabricated by electrochemistry using new approaches for photovoltaic applications. Thin films were electroplated by cathodic polarization on a copper foil or indium tin oxide (ITO) substrates. The optimum deposition conditions (composition, pH and temperature of the electrolyte and applied potential) of the layers as thin films have been identified; in particular the conditions that allow getting the n-type layers have been well identified for the first time. The configuration of a photo - electrochemical cell was used to characterize the spectral response of the layers. It was shown that the p type layers exhibit a photocurrent in the cathode potential region and n layers exhibit photo current in the anode potential region. Measurements of electrical resistivity of electro chemically deposited layers of p and n type Cu2O, showed that the resistivity of p-type Cu2O varies from 3.2 × 105 to 2.0 × 108 Ωcm. These values depend the electrodepositing conditions such as the pH of the solution, the deposition potential and temperature. The influence of several plating parameters of the p-type layers of Cu2O, such as applied potential, pH and temperature of the bath on the chemical composition, degree of crystallinity, grain size and orientation parameters of the sample was systematically studied using X-ray diffraction and scanning electron microscopy. Depending of the electro-deposition potential, two different surface morphologies with various preferential crystal orientations were obtained for the temperatures of the electro-deposition of 30 ° C and pH 9. For the same temperature, the layers of p-type Cu2O of highly crystalline p-type are obtained at pH 12, indicating that the crystallinity depends on the pH of the bath. Also, it has been shown that the morphology of Cu2O layers was changed by varying the potential and the duration of deposition, as well as the temperature of the solution. The conditions for the electro-deposition of Cu2O n-type were identified consistently for the first time. The electro-deposition electrolyte is based 0.01M acetate copper and 0.1 M sodium acetate: it has a pH between 6.3 and 4, a potential of from 0 to -0.25 V vs. Ag / AgCl and a temperature of 60oC. The optimum annealing temperature of the n-type Cu2O layers is between 120-150oC for the annealing time of 30 to 120 minutes. Resistivity of the n-type films varies between 5x103 and 5x104 at pH 4 to pH 6.4. We have shown for the first time that bubbling nitrogen gas in the electroplating cell improves significantly the spectral response of the electro-deposited n-type thin film. A two steps electro-deposition process was implemented to make the p-n homojunction cuprous oxide. Indium tin oxide (ITO) was used as a transparent conductive oxide substrate. A p-Cu2O was electrodeposited on ITO. After heat treatment a thin film layer of n-Cu2O was electrodeposited on top of previous layer. The performance of a p-n homojunction photovoltaic solar cell of Cu2O was determined. The short-circuit current and the open circuit voltage were respectively determined to be as 0.35 volts and 235 μA/cm2. The fill factor (FF) and conversion efficiency of light into electricity were respectively measured to be 0.305 and 0.082%.