Promising Strategy To Improve Charge Separation in Organic Photovoltaics: Installing Permanent Dipoles in PCBM Analogues

Abstract

A multidisciplinary approach involving organic synthesis and theoretical chemistry is applied to investigate a promising strategy to improve charge separation in organic photovoltaics:installing permanent dipoles in fullerene derivatives. Firstly, a PCBM analogue with a permanent dipole in the side-chain (PCBDN) and its reference analogue without a permanent dipole (PCBBz) were successfully synthesised and characterised. Secondly, a multiscale modelling approach was applied to investigate if a PCBDN environment around a central donor-acceptor complex indeed facilitates charge separation. Alignment of the embedding dipoles in response to charges present on the central donor-acceptor complex enhances charge separation. The good correspondence between experimentally and theoretically determined electronic and optical properties of PCBDN, PCBBz and PCBM indicates that the theoretical analysis of the embedding effects of these molecules gives a reliable expectation for their influence on the charge separation process at a microscopic scale in a real device.This work suggests the following strategies to improve charge separation in organic photovoltaics: installing permanent dipoles in PCBM analogues and tuning the concentration of these molecules in an organic donor/acceptor blend.3

The Impact of Sequential Fluorination of π‐Conjugated Polymers on Charge Generation in All‐Polymer Solar Cells

“…In order to examine the fluorination effects of ANTh‐substituted polymer donors on their properties, the P1 – P3 were synthesized via Stille polymerization (Scheme S1, Supporting Information). [10b] The detailed procedures for the synthesis of polymers ( P1 – P3 and P(NDI2HD‐T2) ) are described in the Experimental Section (Supporting Information). Figure a represents the molecular structures of a series of polymer donors with different numbers of fluorine atoms (0, 1F, 2F) and poly[( N , N′ ‐bis(2‐hexyldecyl)napthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl)‐alt‐5,5′‐(2,2′‐bithiophene)] ( P(NDI2HD‐T2) ) polymer acceptor used in this study.…”

“…Also, Havenith and co‐workers showed that enhancing dipole moments in fullerenes can increase charge generation efficiency. [10a] Although there have been a few successful investigations on the correlation between Δ µ ge and photovoltaic parameters ( J SC and FF) in fullerene‐based PSCs, the influence of Δ µ ge of π‐conjugated polymers on charge generation of all‐PSCs has yet to be explored. This model study aims to provide an understanding of the impact of Δ µ ge of π‐conjugated polymers in order to overcome poor charge generation and enhance the PCE value of the all‐PSCs.…”

High dielectric constant conjugated materials for organic photovoltaics

“…The Hummelen group recently also presented a promising strategy to improve charge separation by installing permanent dipoles in fullerene adducts (31 and 32; Figure 6). 55 Although no dielectric constants were measured for the synthesized fullerene derivatives, enhanced dipole moments were calculated when specific functional groups were introduced to increase the electronic polarization. Modeling showed that addition of a certain amount of derivative 31 to the active layer blend facilitated charge separation in the proximity of the central donor-acceptor complex.…”

Donor Conjugated Polymers with Polar Side Chain Groups: The Role of Dielectric Constant and Energetic Disorder on Photovoltaic Performance

“…Using density functional theory calculations, Kraner et al have shown that adding polar groups could be an effective way to increase the dielectric constants of conjugated materials. Several groups have attempted to modify fullerenes to increase the dielectric constant by polar substituents, showing an increase in dielectric constants from 3.9 to ≈5 . While Donaghey et al reported nonfullerene acceptors with remarkably high dielectric constants up to 9.8 by adding oligo(ethylene oxide) chains to the backbones, no device performance was reported .…”