Solar Energy Materials & Solar Cells 220 (2021) 110843 Available online 19 October 2020 0927-0248/© 2020 Elsevier B.V. All rights reserved. Vacancies induced enhancement in neodymium doped titania photoanodes based sensitized solar cells and photo-electrochemical cells Venkata Seshaiah Katta a , Aparajita Das b , Reshma Dileep K. c , Goutham Cilaveni d , Supriya Pulipaka e , Ganapathy Veerappan c , Easwaramoorthi Ramasamy c , Praveen Meduri e , Saket Asthana d , Deepa Melepurath b , Sai Santosh Kumar Raavi a, * a Ultrafast Photophysics and Photonics Laboratory, Department of Physics, Indian Institute of Technology Hyderabad, Kandi, 502285, Telangana, India b Department of Chemistry, Indian Institute of Technology Hyderabad, Kandi, 502285, Telangana, India c Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur, Hyderabad, India d Advanced Functional Materials Laboratory, Department of Physics, Indian Institute of Technology Hyderabad, Kandi, 502285, Telangana, India e Department of Chemical Engineering, Indian Institute of Technology Hyderabad, Kandi, 502285, Telangana, India A R T I C L E INFO Keywords: Rare-earth doped titania Photoanodes Dye-sensitized solar cells Quantum dot sensitized solar cells Photo-electrochemical water splitting ABSTRACT Herein we present a comprehensive study of composition dependent Neodymium (Nd 3+ ) doped Titania (Nd- TiO 2 ) as photoanodes for obtaining improved performances in different types of solar energy conversion devices, namely dye-sensitized solar cell (DSSC), quantum-dot (QD) sensitized solar cells (QDSC) and photo- electrochemical cells (PEC). An all-inclusive characterization of the optical, dielectric properties and morpho- logical studies of Nd-TiO 2 with different doping concentration are performed. The XPS and Urbach energy analysis corroborated further by the dielectric studies established the critical role of vacancies in the improved electrical properties of doped TiO 2 in comparison with that of undoped TiO 2 . Superior performances on solar cells devices (DSSC and QDSC) and PEC water splitting devices using N719 dye and CdS-QD sensitized Nd-TiO 2 photoanodes were fabricated and analyzed. Enhanced photo-conversion effciencies of ≈30% for QDSC and ≈16% for DSSC were obtained with Nd (0.4 mol%)-TiO 2 photoanodes in comparison with undoped TiO 2 pho- toanodes. Similarly, the PEC water splitting of CdS (QDs) sensitization exhibited the photocurrent density of (1.8 mA-cm 2 at 1.23 V vs RHE), which is three times higher than undoped TiO 2 , while the N719 dye-sensitized photoanode exhibited the current density of (0.7 mA-cm 2 at 1.23 V vs RHE), which is two times higher than undoped TiO 2 . The results established that the optimized doping concentration of Nd (0.4 mol%)-TiO 2 is uni- versal for all classes of solar energy conversion devices. 1. Introduction A favorable position of the conduction band, wide bandgap, rela- tively low fabrication costs, stable electrical resistance states, high electron drift mobility high electron lifetimes make titanium dioxide (TiO 2 ) , ubiquitous in various photovoltaic, photocatalytic and water splitting applications [1–10]. Specifc to photovoltaic applications, both mesoporous TiO 2, and compact TiO 2 layers are routinely used as elec- tron acceptors in dye-sensitized solar cells [11,12], perovskite solar cells [13–16], as electron extraction/transport layers in bulk heterojunction solar cells [17–20] and as photoanodes for photoelectrocatalytic con- version of solar energy to electricity and hydrogen [21–24]. Nonethe- less, numerous studies have shown the presence of a high density of electronic trap states lying below the CB as a major limitation for the applications of TiO 2 electrodes [25–29]. Doping TiO 2 with various ele- ments was found to be an easy way to come over this limitation like aiding in improved electronic properties, reduced charge recombina- tion, increased electron transport, faster electron injection, and favor- able shifting the band-edge [30–41]. In general, upon doping TiO 2 , a downward shift conduction band (CB) position results in an increased electron injection [38,42], while an upwards shift increased the open-circuit voltage (V oc ) [43,44]. Furthermore, doping also plays an important role in modifying the oxygen vacancies which play a major role in a variety of technological applications [30,45–47]. Over the last two decades, many dopants like alkali metals (Li Mg, Ca, etc.), metalloids (B, Si, Ge, Sb, etc.), non-metals (C, N, F, etc.), * Corresponding author. E-mail address: sskraavi@phy.iith.ac.in (S.S.K. Raavi). Contents lists available at ScienceDirect Solar Energy Materials and Solar Cells journal homepage: http://www.elsevier.com/locate/solmat https://doi.org/10.1016/j.solmat.2020.110843 Received 25 June 2020; Received in revised form 1 October 2020; Accepted 10 October 2020