Ming ZHANG, MCF, Université Paris-Sud - Centre de Nanosciences et de Nanotechnologies, Directeur de thèse

Pierre JOSEPH, Chargé de Recherche, Laboratoire d'analyse et d'architecture des systèmes CNRS, Examinateur

Wilfried UHRING, Professeur, Université de Strasbourg - Laboratoire ICube - UMR 7357, Examinateur

Philippe LECOEUR, Professeur, Université Paris-Sud - Centre de Nanosciences et de Nanotechnologies, Examinateur

Anne-Marie HAGHIRI-GOSNET, Directeur de recherche, Centre de Nanosciences et de Nanotechnologies - CNRS, Invité

Antoine PALLANDRE, Professeur, Université Paris-Sud - Laboratoire de Chimie Physique UMR 8000 CNRS, Invité

Jury members :

Maria TCHERNYCHEVA, Directeur de Recherche, Université Paris-Sud,Directeur de thèse

Anna FONTCUBERTA I MORRAL, Professeur, École Polytechnique Fédérale de Lausanne,Rapporteur

Julien PERNOT, Professeur, Université Grenoble Alpes, Rapporteur

François JULIEN, DRCE,Université Paris-Sud,Examinateur

Jean-Yves DUBOZ, Directeur de Recherche,CNRS-CRHEA,Examinateur

Heinz SCHMID,Research Staff Member,IBM Reasearch Examinateur

Abstract :

Although III-V nanowires (NWs) are recognized as promising candidates for the development of new generation solar cells thanks to their very attractive optical properties, the expected performance improvement over their 2D counterparts has not yet been demonstrated. To understand the origin of the existing gap between the theoretical predictions and the experimental demonstrations, investigation of the material properties down to the nanometric scale is fundamental. Nanoscale analyses are expected to elucidate the limiting factors (e.g. the electrical properties of internal p-n junctions, the wire-to-wire homogeneity and eventual failures) and to propose solutions for enhancing the performance of NW photovoltaic (PV) devices.
This PhD thesis applies the electron beam probe techniques to get access to the key parameters governing the PV conversion at a single NW level in order to further optimize the properties of III-V NWs grown on Si.
First, GaAs and AlGaAs NWs containing a radial junction are investigated at the nanoscale and their internal structure is optimized accounting for the feedback from the experimental findings. The characterization of mm-sized devices confirms the improvement of the device performance at the macroscopic level.
Then InGaP NWs grown by a novel Template Assisted Selective Epitaxy (TASE) method containing an axial junction are studied. The doping level in the ternary alloy is estimated by the electron beam induced current microscopy and the photovoltaic response of these structures is demonstrated for the first time. The electrical properties of GaAs NWs grown with the same technique are also characterized.
Finally, InP/InGaP dual junction NWs are characterized to demonstrate the first fully nanostructured tandem solar cell. Although an electrical activity is observed under excitation in both top and bottom junctions, the tandem performance is limited by the electrical properties of the tunnel junction which connects them.

Mots clés en anglais :

Nanowire,solar cell,third generation