Understanding the Role of Order in Y‐Series Non‐Fullerene Solar Cells to Realize High Open‐Circuit Voltages

Abstract

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/aenm.202103422.

Identifying the Signatures of Intermolecular Interactions in Blends of PM6 with Y6 and N4 Using Absorption Spectroscopy

“…The observed dependence of the device performance on the processing conditions and blend composition suggested a strong role of the molecular arrangements and order in the blend film. [24][25][26][27] This insight was further supported by the observation that side-chain modifications have a great impact on device performance. Side-chain modifications are well-known to alter the aggregation behavior and long-range order.…”

“…Side-chain modifications are well-known to alter the aggregation behavior and long-range order. [23,[25][26][28][29][30][31][32][33][34][35][36][37][38][39][40] It is well-known that the performance of OSCs does not only depend on the material itself, but rather on the arrangement and orientation of individual molecules with respect to neighboring molecules. It is the local morphology and the resulting intermolecular interactions that control the energy levels as well as optical and electronic properties of the material, including the efficiency of exciton dissociation and charge extraction in a device.…”

“…[26,45] We are ultimately interested in blend films of PM6:Y6 and PM6:N4, which have previously been used by some of us to study the role of structural and energetic disorder on free charge recombination and open circuit voltage (V OC ). [25] For this, we will first identify the signatures of intermolecular interactions that show in solutions upon cooling, which is a well-established approach. [46][47][48][49][50][51][52] Cooling down the solution decreases the quality of the solvent.…”

Effects of energetic disorder in bulk heterojunction organic solar cells

“…The interrelation between structural order, energetic disorder and device performance was highlighted in a recent study by Neher and co-workers. 97 Here, the authors performed temperature-dependent charge transport, charge recombination and V OC studies on blends of PM6 with either Y6 or N4. Compared to Y6, N4 exhibits slightly longer side chains, with the result of better solubility, less strong aggregation, and stronger intermixing with the PM6 donor phase.…”

Spectroelectrochemically determined energy levels of PM6:Y6 blends and their relevance to solar cell performance

“…36 This is because an electron–hole pair in the charge separated state has many more options to distribute in the blend volume than when it is bound in an exciton or in a charge transfer state. 75 However, our own recent studies showed a pronounced decrease of the free carrier density with temperature, 76 which questions a strong contribution by entropy-driven processes. An alternative approach is to consider the presence of sub-bandgap states not accessible by our spectroscopy.…”