Synthesis, Morphological Analysis and Photovoltaic Performance of Thallium- and Yttrium-Doped Titanium Dioxide-Based Dye-Sensitized Solar Cells SADIA BAIG, 1 MUHAMMAD SAIFULLAH AWAN, 2 SALEEM AKHTAR, 3 and SAFEER AHMED 1,4 1.—Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan. 2.—National Centre for Physics, Quaid-i-Azam University, Islamabad 45320, Pakistan. 3.—Ibn-i- Sina Institute of Technology, H-11, Islamabad, Pakistan. 4.—e-mail: safeerad@qau.edu.pk Thallium (Tl) and yttrium (Y) have been doped separately, as an extrinsic impurity, into titania (TiO 2 ) matrix to investigate the effect of dopant ion on the photovoltaic properties of the resultant dye-sensitized solar cells (DSCs). The metals were selected on the basis of their electrical conductivities. Two types of DSCs were fabricated: the first type with a single semiconductor layer of either pure TiO 2 or Tl- or Y-doped TIO 2 , and the second type was of double- layered cells having a nanocrystalline TiO 2 foundation layer and above it mesoporous TiO 2 (pure or doped) as a scattering layer. X-ray diffraction and scanning electron microscopy analyses revealed the formation of composite- like Tl 4 O 3 structures in an anatase matrix of annealed Tl-doped titania, whereas Y limited the nucleation and growth process and resulted in smaller particles. UV–visible and photoluminescence spectroscopies showed obvious improvement in the optical properties of TiO 2 with Tl doping, whereas Y ad- versely affected the film characteristics. The resultant photo-anodes in DSCs under 100 mW cm 2 light illumination gave a photovoltaic conversion effi- ciency of 1.07% for pure TiO 2 , while Y-doped and Tl-doped TiO 2 showed 0.36% and 3.63% efficiency, respectively. The findings were ascribed mainly to the relative electrical conductivities and partially to the morphological structures of the doped samples. Key words: Dye-sensitized solar cells, doped titania, scattering layer, thallium, yttrium, electrical conductivity INTRODUCTION A dye-synthesized solar cell (DSC) is a photo- voltaic (PV) energy conversion device, and one of the top researched areas of solar cells. Phenomenolog- ically, a DSC is an assembly of a photosensitizer (usually a light absorbing dye), electron and hole transporting phases and an electron collecting substrate. 1,2 The electron transporting phase is a semiconductor material, having overriding impor- tance next to the photosensitizer, which acts as a photo-anode for effective charge transport from dye to external circuit. A multifunctional semiconductor such as titania (TiO 2 ) is the most promising mate- rial for DSCs due to its high electron mobility, large excitonic binding energies and wide band gap. 3,4 Extremely extensive work has been carried out on the synthesis and characterization of TiO 2 from almost every possible aspect, and it still continues, as documented in following paragraphs. The principal role of a sensitizer can be assisted by providing large numbers of photo-excited elec- trons. This is possible by having more and more adsorbed dye molecules on the semiconductor sur- face that reduce the probability of carrier recombi- nation. 5 The charge carriers are produced once the (Received April 19, 2018; accepted July 6, 2018; published online July 20, 2018) Journal of ELECTRONIC MATERIALS, Vol. 47, No. 10, 2018 https://doi.org/10.1007/s11664-018-6506-0 Ó 2018 The Minerals, Metals & Materials Society 6193