Asymmetric Dual Anchoring Sensitizers/Cosensitizers for Dye Sensitized Solar Cell Application: An Insight into Various Fundamental Processes inside the Cell Rajalakshmi Kesavan, † Fathy Attia, ‡ Rui Su, ‡ P. Anees, § Ahmed El-Shafei,* ,‡ and Airody Vasudeva Adhikari* ,† † Organic Materials Laboratory, Department of Chemistry, National Institute of Technology Karnataka, Surathkal, Mangalore 575 025, India ‡ Polymer and Color Chemistry Program, North Carolina State University, Raleigh, North Carolina 27695, United States § Materials Physics Division, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamil Nadu 603 102, India * S Supporting Information ABSTRACT: To study the various fundamental processes occurring inside the dye sensitized solar cell (DSSC), we have fabricated devices employing newly synthesized diphenylamine-based organic dyes with A-D-π-A configuration, carrying four different anchoring groups, namely, cyanoacetic acid (DDC), rhodanine acetic acid (DDR), 4-hydrazinylbenzoic acid (DDH), and barbituric acid (DDB), as effective sensitizers/cosensitizers. In the present work, all the bianchoring dyes were subjected to photophysical, electrochemical, thermodynamic, photoelectrochemical, and theoretical studies. All of them displayed characteristic λ abs and λ emi in the range of 415−480 and 570−680 nm, respectively. Their optical and electrochemical band gaps were calculated to be in the order of 2.1 to 2.3 eV. The calculated driving forces for electron injection (ΔG inj ), recombination (ΔG inj ), and regeneration (ΔG reg ) processes were found to be negative, showing the feasibility of these processes, while their DFT studies clearly indicated the directional flow of electrons within the dye in the cell. The devices with DDC as sensitizer displayed the highest conversion efficiency of 2.53%, whereas DDB exhibited the maximum of 7.69% when employed as a cosensitizer along with Ru (II) based HD-2 dye. Finally, EIS circuit fitting was carried out in order to obtain different interface resistance values to study the fundamental processes of energy conversion. ■ INTRODUCTION Globally, the escalating demand for renewable energy sources has led to the necessity of capturing and utilizing solar energy as an alternative energy source. 1−4 Among the various processes of solar energy utilization, the dye sensitized solar cells (DSSCs) process is a promising photovoltaic technology because of its low cost, simple manufacturing process, and tunable optical properties. 5,6 Gratzel and co-workers in 1991 reported DSSCs sensitized with a Ru(II)-complex based dye for the first time. Since then, academics and industry have given considerable attention to DSSCs in efforts to develop highly efficient devices. Among the four major components, the sensitizer (dye) that adsorbs chemically to the semi- conductor is a key component in a DSSC. It facilitates the absorption of light and transfer of electrons to the semi- conductor, TiO 2 . 7,8 An ideal dye requires certain features such as appropriate HOMO and LUMO levels for the regeneration of dye from the electrolyte and charge injection to the conduction band (CB) of TiO 2 , a good anchoring group for binding with TiO 2 , and a broad absorption power in addition to good photostability. During the DSSC operating cycle, the efficient injection of electrons to the CB (0.5 V vs NHE) of TiO 2 by the excited dye (S*) and effective dye regeneration or rereduction bring about the improvement in photovoltaic parameters such as the photocurrent density (J SC ), the open circuit photo voltage (V OC ), and fill factor (FF), which results in further increase in the power conversion efficiency, PCE(η) of the devices. 1,2,9 However, the unwanted processes, namely, recombination of the injected electrons in CB of TiO 2 by the oxidized sensitizer (recombination) or with I 3 − in the solution (dark current) also exist during the cell operation, which leads to lower J SC and V OC values. Evidently, for an efficient device with greater J SC and V OC , the electron injection and regeneration processes should be faster than recombination and dark current, for which an appropriate dye selection is most essential. 1,2 Even though devices with ruthenium-based chromophores such as HD-2, N3, N719, and black dye are giving high PCE values, the high cost of ruthenium, scarcity of the metal, and tedious Received: July 10, 2019 Revised: September 11, 2019 Published: September 16, 2019 Article pubs.acs.org/JPCC Cite This: J. Phys. Chem. C 2019, 123, 24383-24395 © 2019 American Chemical Society 24383 DOI: 10.1021/acs.jpcc.9b06525 J. Phys. Chem. C 2019, 123, 24383−24395 Downloaded via NORTH CAROLINA STATE UNIV on October 11, 2019 at 21:33:15 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.