Fabrication of High V_OC Organic Solar Cells with a Non-Halogenated Solvent and the Effect of Substituted Groups for “Same-A-Strategy” Material Combinations

Abstract

We report a class of high-voltage organic solar cells (OSCs) processed by the environmentally friendly solvent tetrahydrofuran (THF), where four benzotriazole (BTA)-based p-type polymers (PE31, PE32, PE33, and J52-Cl) and a BTA-based small molecule BTA5 are applied as p-type and n-type materials, respectively, according to “Same-A-Strategy” (SAS). The single-junction OSCs based on all four material blends exhibit a high open-circuit voltage (V OC) above 1.10 V. We systematically study the impact of the three different substituents (−OCH3, −F, −Cl) on the BTA unit of the polymer donors. Interestingly, PE31 containing the unsubstituted BTA unit shows the efficient hole transfer and more balanced charge mobilities, thus leading to the highest power conversion efficiency (PCE) of 10.08% with a V OC of 1.11 V and a J SC of 13.68 mA cm–2. Due to the upshifted highest electron-occupied molecular orbital (HOMO) level and the weak crystallinity of the methoxy-substituted polymer PE32, the resulting device shows the lowest PCE of 7.40% with a slightly decreased V OC of 1.10 V. In addition, after the chlorination and fluorination, the HOMO levels of the donor materials PE33 and J52-Cl are gradually downshifted, contributing to increased V OC values of 1.16 and 1.21 V, respectively. Our results prove that an unsubstituted p-type polymer can also afford high voltage and promising performance via non-halogenated solvent processing, which is of great significance for simplifying the synthesis steps and realizing the commercialization of OSCs.

Elucidating Charge Generation in Green-Solvent Processed Organic Solar Cells

“…In these samples, strong PL quenching of the blend compared to the neat was observed; indicating domain size compatible with exciton diffusion length [48]. Similar observation was reported for the study of benzotriazole (BTA)-based p-type polymers (PE31, PE32, PE33, and J52-Cl) when blended with a BTAbased small molecule BTA5 using THF [47]. It was shown that PE31:BTA5 exhibited the highest PCE of 10.08%, which correlated with the highest PL quenching, whilst the other blends had reduced PL quenching; insinuating less optimum morphology of domain size.…”

“…Such a result is ascribed to a better packing of the compounds leading to a good level of intermolecular organization. In contrast, due to the weak crystallinity of the methoxy-substituted polymer PE32, the resulting device shows the lowest PCE of 7.40% [47]. All polymer solar cells were prepared by Sunsun et al using a perylenediimide (PDI)-bithiophene-based polymer acceptor PPDIODT, and PBDT-TS1 as polymer donor.…”

M‐Series Nonfullerene Acceptors with Varied Fluorinated End Groups: Crystal Structure, Intermolecular Interaction, Charge Transport, and Photovoltaic Performance

“…[28][29][30][31][32] Among different types of halogenations, fluorination is one of the most important molecular design strategies to further improve the performance of PSCs. [33][34][35][36][37][38][39][40][41] First, due to the strong electron-withdrawing effect with a very small size, the introduction of fluorine atom is beneficial to simultaneously downshift the frontier molecular orbitals and to reduce the optical bandgap without using a large π-conjugated system. Second, the formation of noncovalent interactions, such as F•••H and F•••S, can effectively reduce the intermolecular π-π stacking distance, leading to improved charge transport properties of the resulting NFAs.…”

Electron Distribution in 1,2,3-Benzotriazole and 1,2,3-Triazole Anion Radical Isomers: An EPR and DFT Study

“…More recently, there has been increased interest in these heterocycles for their use in organic materials consisting of π-conjugated electron-donor and electron-acceptor polymers (i.e., n-type and p-type materials, respectively). − These conjugated polymers show promise for use in organic photovoltaics, organic light-emitting diodes, and high-voltage solar cells. ,,,, Recently, a great deal of attention has focused on the N2-benzotriazole moiety as an important molecular linker in such polymers because of its significant electron-withdrawing properties, which make it a valuable substituent in p-type materials. , Scheme (upper) contains an example of a monomeric unit containing the N2-benzotriazole moiety, which is considered to be an electron acceptor in this polymer . Notably, recent studies have demonstrated that the N2-benzotriazole moiety is versatile and can be incorporated into both electron-accepting and electron-donating polymeric materials when appropriate functional groups are attached …”

“…10−18 These conjugated polymers show promise for use in organic photovoltaics, organic light-emitting diodes, and high-voltage solar cells. 12,14,15,17,18 Recently, a great deal of attention has focused on the N2-benzotriazole moiety as an important molecular linker in such polymers because of its significant electron-withdrawing properties, which make it a valuable substituent in p-type materials. 11,12 Scheme 1 (upper) contains an example of a monomeric unit containing the N2benzotriazole moiety, which is considered to be an electron acceptor in this polymer.…”