The C₇₀ Fullerene Adducts with Low Anisotropy of Polarizability are More Efficient Electron Acceptors for Organic Solar Cells. The Minimum Anisotropy Hypothesis for Efficient Isomer-Free Fullerene-Adduct Photovoltaics

Abstract

Currently, higher fullerene adducts (bis-, tris-, and multiadducts) come into use as electron acceptor components for organic solar cells (OSCs) with enhanced output parameters. These compounds have numerous positional isomers, and isomerism crucially influences the performances of photovoltaic devices. Indeed, application of the isolated and purified fullerene adducts (isomer-free fullerene-adduct OSCs) allows increasing power conversion efficiency (PCE) compared to the use of the isomeric mixtures. Previously, we have found that OSCs reveal higher PCE if they utilize the C 60 bisadducts with the lowest anisotropy of polarizability. To demonstrate a general nature of the found correlation in the present work, we have theoretically studied anisotropy of polarizability of the selected isomeric C 70 mono-, bis-, and higher adducts synthesized and separately tested as OSC electron acceptors in recent experimental works. We have found that, as in the case of C 60 , less-anisotropic C 70 derivatives reveal higher PCE of the corresponding photovoltaic devices. Thus, the correlation between anisotropy of polarizability of fullerene acceptors and power conversion efficiency of OSC based on them has a general nature (regardless of the fullerene type and nature of addends), and we can formulate the minimum anisotropy hypothesis: f ullerene adducts with low anisotropy of polarizability are more ef f icient as electron acceptor materials for organic solar cells than their highly anisotropic regioisomers. This conjecture is supported with congruence of relevant experimental and computational data with scarce exceptions and may be recommended as an auxiliary tool for the molecular design and screening of novel fullerene derivatives promising for organic solar cells. The reasons for the importance of polarizability (and its anisotropy) underlying this principle are discussed.

Polarizability in Astrochemical Studies of Complex Carbon-Based Compounds

“…Previously, we systematically studied the polarizability of fullerene derivatives and stressed its crucial role for chemistry and materials science . For example, it reflects the features of interacting fullerene adducts with irradiation in organic solar cells , and molecular switches or screening atoms and small molecules trapped inside the fullerene cages. , Expectedly, the polarizability of fullerenes was invoked to analyze the chemical properties of these species. This field has been intensively explored, and there are approaches based on the analysis of polarizability ellipsoids of fullerenes, , site-specific polarizabilities associated with the molecular moieties, , and the use of the polarizability of the molecule in total. , Below, we focus on the applications of the minimum-polarizability principle to the fullerene-based systems with astrochemical relevance.…”

In‐depth probe of researching interfacial charge transfer process for organic solar cells: A promising bisadduct fullerene derivatives acceptor

“…The influence of regioisomers was also explored more rigorously when building the model in the Section S.4. of the Supporting Information . According to the minimum anisotropy of polarizability principle, the bisadduct isomers with extremum values (the MOST and the LEAST) of were selected by calculating the anisotropy of polarizability to further consider the effect of isomerism on CT mechanism.…”

“…of the Supporting Information. [47] According to the minimum anisotropy of polarizability principle, the bisadduct isomers with extremum values (the MOST and the LEAST) of were selected by calculating the anisotropy of polarizability to further consider the effect of isomerism on CT mechanism. Notably, among B60 and its isomers, B60 has the largest anisotropy value, so B60 is B60-MOST.…”

cis-1 Isomers of tethered bismethano[70]fullerene as electron acceptors in organic photovoltaics

“…However, the number of reports that demonstrate this is limited [36][37][38][39] compared to the case of regioisomer-free [60]fullerene bis-adducts. [23][24][25][26][27][28][29][30][31][32][33][34][35] This is due to the synthetic difficulty originating from the formation of a complicated mixture containing multiple regioisomers of [70] fullerene bis-adducts.…”

“…Regioisomer-controlled [70]fullerene bis-adducts are expected to be high-performance acceptors for BHJ OPVs, as is evident from the above argument. However, the number of reports that demonstrate this is limited 36–39 compared to the case of regioisomer-free [60]fullerene bis-adducts. 23–35 This is due to the synthetic difficulty originating from the formation of a complicated mixture containing multiple regioisomers of [70]fullerene bis-adducts.…”