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

D A Duarte,M Massi,A S Da Silva Sobrinho

doi:10.1155/2014/839757

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.

Highlights

Since the dye-sensitized solar cells (DSSCs) were introduced by O’Regan and Graetzel in the early 90s [1] several studies were conducted aiming to improve the light-to-electricity conversion of the DSSCs by modifying various cell components, including the transparent conductive oxides [2], light absorbers [3], redox electrolytes [4], counter-electrodes [5], and the TiO2 structure [6,7,8]
They were analyzed by profilometry, X-ray diffraction (XRD), optical spectrophotometry, atomic force microscopy (AFM), Rutherford backscattering spectroscopy (RBS), and X-ray photoelectron spectroscopy (XPS)
The results show that the higher JSC was achieved for DSSC built with the nitrogen-doped anatase TiO2

Summary

Introduction

Since the dye-sensitized solar cells (DSSCs) were introduced by O’Regan and Graetzel in the early 90s [1] several studies were conducted aiming to improve the light-to-electricity conversion of the DSSCs by modifying various cell components, including the transparent conductive oxides [2], light absorbers [3], redox electrolytes [4], counter-electrodes [5], and the TiO2 structure [6,7,8]. Some experimental investigations [25, 26] reported a sudden reduction in the energy band gap of nitrogen-doped TiO2 prepared by reactive sputtering once this technique combines the oxidation of TiN and chemisorption of reactive gas particles [27]. Berg’s model and conducted by our group [32] show that there is an optimal gas mixture for deposition of nitrogendoped TiO2 by reactive sputtering in which the band gap is reduced This finding is consistent with several experimental results obtained elsewhere. An original numerical model was used to simulate the reactive sputter deposition of nitrogen-doped TiO2 in order to study the growth mechanism of the films and understand how the substitutional nitrogen is incorporated in the film lattice during the reactive deposition

Experimental Setup and Model Input Data

Results and Discussions

Cell C

Conclusions