Estimation of the energy levels of the donor–acceptor polymers of organic solar cells using cyclic voltammetry

Cyclic voltammetry is a powerful electrochemical tool for obtaining electrical properties as energy levels in polymers. Herein, it has been used to estimate the HOMO and LUMO energy levels of the donor and acceptor polymers, P3HT and PC₆₁BM, by varying of GeS₂ nanoparticles, in addition to estimating other parameters such as the E_g, ΔLUMO, and the theoretical V_oc. The data obtained were contrasted with an experiment of P3HT:PC₆₁BM:GeS₂ inverted organic solar cells to determine the influence of GeS₂ on the energy levels and the reported solar efficiency. Without the addition of nanoparticles to the polymer samples, an E_g of 1.88 eV and 2.25 eV was obtained for P3HT and PC₆₁BM, respectively. In addition, a V_oc of 1.13 V and an E_dis of 0.76 V were found. However, the addition of GeS₂ nanoparticles modified these values, finding a substantial improvement with 0.75 wt% of GeS₂ modifying the E_g to 1.47 eV and 2.52 eV for the P3HT and the PC₆₁BM, respectively, with a V_oc of 1.31 V and an E_dis of 0.15 V. A correlation was found between the estimated theoretical V_oc with the experimental V_oc and the PCE. Precisely, the best experimental result was with 0.75 wt% of nanoparticles, obtaining a maximum efficiency of 2.18 % and an average device efficiency of 1.99 %.