Minimizing geminate recombination losses in small-molecule-based organic solar cells

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Vol. 7; no. 22; pp. 6641 - 6648
• Main Authors: Sandoval-Torrientes, Rafael, Gavrik, Alexey, Isakova, Anna, Abudulimu, Abasi, Calbo, Joaquín, Aragó, Juan, Santos, José, Ortí, Enrique, Martín, Nazario, Dyakonov, Vladimir, Lüer, Larry
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 2019
• Subjects: Donors (electronic); Mathematical analysis; Organic chemistry; Photovoltaic cells; Quantum chemistry; Solar cells; Spectrum analysis
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/c9tc00862d

Small-molecule-based organic solar cells (OSCs) are a recurrent alternative to polymer-based OSCs. Due to the higher purity and definition of small molecules compared to polymers, the morphological requirements can be more relaxed. Here, we present a series of novel rhodanine-based small-molecule electron donors and blend them with the standard acceptor PC70BM. By performing a target analysis on femtosecond spectroscopy data, we quantify the rates of geminate charge recombination. We are able to reproduce these rates by applying the Marcus-Levich-Jortner equation, using results from quantum chemical calculations. This shows that in a series of differently substituted compounds, one can correctly predict trends in geminate recombination rates by relying only on quantities that are easy to measure (cyclic voltammetry, optical spectra) or that can be calculated by relatively inexpensive methods such as (TD)DFT. Our method should thus accelerate the search for high-performance small-molecule photovoltaic blends. Geminate recombination rates are successfully predicted for series of small-molecule bulk heterojunction solar cells applying the Marcus-Levich-Jortner equation.