Stephane Taunier

Ab initio calculation of intrinsic point defects in CuInSe2

Abstract Preliminary ab initio calculation of different point defects energy and electronic density of states have been performed on the prototype chalcopyrite semiconductor CuInSe 2 . The simulation method used is based on the density functional theory within the framework of pseudo-potentials and plane waves basis. The isolated neutral defects considered are: V Cu , V In , V Se , Cu i , In i , In Cu , Cu In and the complex defects are 2Cu i +Cu In , In Cu +Cu In and 2V Cu +In Cu , some of which being computed for the first time by advanced ab initio techniques. In agreement with previous results, we show that some point defects (such as V Cu ) and pair defects (2V Cu +In Cu ) have very low formation energies. Some energies of formation were found significantly lower than previous estimations. The comparison of the formation energies with the exchange correlation (LDA or GGA) is discussed. The perturbation induced by the presence of some of these ideal defects on the density of states is also presented.

Copper indium diselenide solar cells prepared by electrodeposition

Copper indium diselenide (CIS) layers have been prepared by an electrodeposition based process. The composition, density and adhesion properties of theses films were found to be highly suitable for use as the active layer in a CIS solar cell. After recrystallisation and the completion of the device layer (by the deposition of CdS and ZnO layers), efficiencies as high as 8.8 % were found (total area, 100 MW/cm/sup 2/, no AR coating) for small area devices (0.06 cm/sup 2/). To the best of our knowledge, this is a record efficiency for electrodeposited CIS, without any post additional vacuum deposition process. Promising results have been also obtained on 5/spl times/5 cm/sup 2/ substrates (average efficiency of 4.5 %).

Towards Better Understanding of High Efficiency Cd-free CIGS Solar Cells Using Atomic Layer Deposited Indium Sulfide Buffer Layers

ABSTRACT: This paper presents optimization studies on the formation of cadmium free buffer layers for high efficiency copper indium diselenide (CIGS) thin film solar cells using a vapor phase route. Indium sulfide layers have been deposited on CIGS substrates by Atomic Layer Deposition (ALD) at substrate temperatures between 140 and 260 °C using indium acetylacetonate and hydrogen sulfide precursors. The parametric study of the deposition temperature shows an optimal value at about 220°C, leading to an efficiency of 16.4 % which is a technological breakthrough. The analysis of the device shows that indium sulfide layers give an improvement of the blue response of the cells as compared a standard CdS processed cell, due to a high apparent band gap (2.7-2.8 eV), higher open circuit voltages (up to 665 mV) and fill factor (78 %) . This denotes high interface quality of the system. Atomic diffusion processes of sodium and copper in the buffer layer are evidenced. INTRODUCTION In high efficiency thin film solar cells based on Cu(In,Ga)Se

Efficient Cu(In, Ga)Se 2 Based Solar Cells Prepared by Electrodeposition

CuInSe 2 and Cu(In, Ga)Se 2 precursor layers have been prepared by electrodeposition, with morphologies suitable for device completion. These precursor films were transformed into photovoltaic quality films after thermal annealing without any post-additional vacuum deposition process. Depending on the preparation parameters annealed films with different band gaps between 1eV and 1.5 eV have been prepared. The dependence of resulting solar cell parameters has been investigated. The best efficiency achieved is about 10,2 % for a band gap of 1.45 eV. This device presents an open circuit voltage value of 740 mV, in agreement with the higher band gap value. Device characterisations (current-voltage, capacitance-voltage and spectral response analysis) have been performed. Admittance spectroscopy at room temperature indicates the presence of two acceptor traps at 0.3 and 0.43 eV from the valance band with density of the order of 2. 10 17 cm -3 eV- 1 .