Development of Dye-Sensitized Solar Cells with Sputtered N-DopedTiO2Thin Films: From Modeling the Growth Mechanism of the Films to Fabrication of the Solar Cells

Abstract

In this paper, nitrogen-doped TiO2thin films were deposited by DC reactive sputtering at different doping levels for the development of dye-sensitized solar cells. The mechanism of film growth during the sputtering process and the effect of the nitrogen doping on the structural, optical, morphological, chemical, and electronic properties of the TiO2were investigated by numerical modeling and experimental methods. The influence of the nitrogen doping on the working principle of the prototypes was investigated by current-voltage relations measured under illuminated and dark conditions. The results indicate that, during the film deposition, the control of the oxidation processes of the nitride layers plays a fundamental role for an effective incorporation of substitutional nitrogen in the film structure and cells built with nitrogen-doped TiO2have higher short-circuit photocurrent in relation to that obtained with conventional DSSCs. On the other hand, DSSCs built with nondoped TiO2have higher open-circuit voltage. These experimental observations indicate that the incorporation of nitrogen in the TiO2lattice increases simultaneously the processes of generation and destruction of electric current.

Incorporation of N in the TiO2 Lattice Versus Oxidation of TiN: Influence of the Deposition Method on the Energy Gap of N-Doped TiO2 Deposited by Reactive Magnetron Sputtering

“…Otherwise, the surface is fully oxidized. The overall results of experimental studies about the chemical composition of films deposited in the same conditions are in agreement with the results presented in this paper 11,19 . However, the modeled concentration of suboxides in the steady state condition does not match with XPS data (chemical composition on the film surface) presented in ref.…”

“…The growth mechanisms were evaluated with a numerical model based on Berg model described in refs. 11,19,28 . This model is a set of ODEs that describe the temporal evolution of the chemical composition of the films that were assumed as a mixture of several compounds, such as, TiO, Ti 2 O 3 , TiO 2 , TiN and substitutional nitrogen (O-Ti-N).…”

“…Based on papers published in the past, films of N-doped TiO 2 is commonly deposited by sputtering of a metallic titanium target with the reactive gas mixture composed by argon, nitrogen and oxygen, where the amount of substitutional nitrogen in the film lattice was found to be very sensitive to the amount of oxygen in the gas phase. This is caused by oxidation of the nitride layers and high sticking coefficient of the oxygen on Ti and TiN; thus, the effective incorporation of substitutional nitrogen is observed only for cases where the nitrogen flow rate is higher than that used for oxygen during film growth 11,16,17,19 . Otherwise, interstitial nitrogen becomes favored 20 and may desorb when the film structure is subject to annealing conditions 21 .…”

“…Otherwise, interstitial nitrogen becomes favored 20 and may desorb when the film structure is subject to annealing conditions 21 . According to previous studies 11,19,22 , oxidation of the nitride layers is one of the main reactions responsible by embedding of substitutional nitrogen in TiO 2 during deposition with continuous gas flow rate feeding (see the pulsed case in ref. 23 ).…”

“…These steps are observed for all conditions where the concentration of substitutional nitrogen (fraction of O-Ti-N) decreases as the oxygen flow rate increases. This effect may be caused by decreasing of the suboxides in the film lattice during oxidation 11 . The estimated percentage of substitutional nitrogen (fraction of O-Ti-N in the steady state condition shown in Figure 2) for films deposited with oxygen flow rates of 0.2, 0.6 and 3.5 sccm are 9, 6 and 1%, respectively.…”