# The BCL Method for DSSC: Basis and Applications +
###### Abstract  
In this work, a comprehensive view of the route that led to the construction of a theoretical approach to the functioning of DSSC is presented. The model was developed based on the theoretical interpretation of experimental results obtained along the years for solar cells including different dyes. This allowed the authors to generate the Barrera, Crivelli, Loeb (BCL) model. The method is based on a system of equations that uses time-dependent density functional theory (TDDFT) calculations to obtain a theoretical index, the Global Efficiency Index (GEI), for the efficiency of a sensitized solar cell. The GEI is obtained through the product of three factors: the available energy for injection, the amount of charge injected, and the efficiency of regeneration. The results so far obtained show a promising correlation with the experimental index of photo conversion efficiency (PCE). Moreover, the method provides theoretical tools that allow us to obtain an understanding of the operation of the cell, and provide us with the keys to optimize it. Its application to other type of devices, as, e.g., the highly more efficient perovskite solar cells, emerges as a challenging future goal. DSSC; solar cells; perovskite; BCL +
Footnote †: We dedicate this work to the memory of Professor [PERSON]. Footnote †: We dedicate this work to the memory of Professor [PERSON]. Footnote †: We dedicate this work to the memory of Professor [PERSON]. Footnote †: We dedicate this work to the memory of Professor [PERSON]. Footnote †: We dedicate this work to the memory of Professor [PERSON]. Footnote †: We dedicate this work to the memory of Professor [PERSON]. Footnote †: We dedicate this work to the memory of Professor [PERSON]. Footnote †: We dedicate this work to the memory of Professor [PERSON]. For more than a decade, our group [5] has focused part of its research on the synthesis, characterization and theoretical description of new ruthenium complexes, with the aim to visualize the main factors responsible for an efficient electronic injection in a dye-sensitized solar cell (DSSC). The research has been centered around two topics: the nature of the anchor group and the enhancement of the optical properties by increasing the extinction molar coefficient, or by red shifting the absorption spectra. Different anchoring ligands were designed, and the corresponding ruthenium complexes synthesized. The electronic behavior of the complex, and its performance as dye for DSSC, was evaluated by different experimental techniques, as well as by DFT calculations. The experimental information was collected, analyzed together with data from the literature, and interpreted to build a theoretical model that could explain the results and provide reasonable guidelines for designing new ligands and complexes in the future. This review shows the route that led to the construction of the BCL model, a theoretical approach that quantifies the efficiency of a given dye through a theoretical index, GEI, the Global Efficiency Index (\(\xi\)). This parameter is parceled in three main contributions: light harvesting, electron injection and regeneration. As a first step, theoretical calculations were planned to study the excited state of several acceptor polipyridinic ligands. The ligands were analyzed by fragments, in order to understand how the different parts of the molecule contribute to the acceptor capacity observed for them. Having applied the fragment decomposition of ligands, this concept was employed to model the electronic transitions in the absorption spectra of the corresponding complexes. The electronic transitions were considered as a sum of single electronic excitations occurring between the different fragments of the molecule. In this sense, it became feasible to identify  
Figure 1: (**a**) Schematic representation of a DSSC device; (**b**) N3 dye; (**c**) BD dye. excitations as intraligand (IL), ligand to ligand (LL), metal to ligand (ML), and ligand to metal (LM).