Effect of Solvent Additives on the Morphology and Device Performance of Printed Nonfullerene Acceptor Based Organic Solar Cells

Abstract

Printing of active layers of high-efficiency organic solar cells and morphology control by processing with varying solvent additive concentrations are important to realize realworld use of bulk-heterojunction photovoltaics as it enables both up-scaling and optimization of the device performance. In this work, active layers of the conjugated polymer with benzodithiophene units PBDB-T-SF and the nonfullerene small molecule acceptor IT-4F are printed using meniscus guided slot-die coating. 1,8-Diiodooctane (DIO) is added to optimize the power conversion efficiency (PCE). The effect on the inner nanostructure and surface morphology of the material is studied for different solvent additive concentrations with grazing incidence small-angle X-ray scattering (GISAXS), grazing incidence wide-angle X-ray scattering (GIWAXS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Optical properties are studied with photoluminescence (PL), UV/vis absorption spectroscopy, and external quantum efficiency (EQE) measurements and correlated to the corresponding PCEs. The addition of 0.25 vol % DIO enhances the average PCE from 3.5 to 7.9%, whereas at higher concentrations the positive effect is less pronounced. A solar cell performance of 8.95% is obtained for the best printed device processed with an optimum solvent additive concentration. Thus, with the largescale preparation method printing similarly well working solar cells can be realized as with the spin-coating method.

Following in Operando the Structure Evolution‐Induced Degradation in Printed Organic Solar Cells with Nonfullerene Small Molecule Acceptor

“…In active layers prepared with solvent additive, so far, a domain shrinkage was reported as a morphology degradation mechanism instead of a domain coarsening . Therefore, for the PBDB‐T‐SF:IT‐4F solar cells of this study being manufactured with 0.25 vol% 1,8‐diiodooctane (DIO) as solvent additive, the observed domain coarsening is unexpected.…”

“…A loss in solvent additive was found responsible for the domain shrinkage in previous works, which is not observed in this study (Figure S5, Supporting Information). This is favorable, as DIO was found to enhance the device performance of printed PBDB‐T‐SF:IT‐4F‐based organic solar cells by provoking the formation of small polymer domains in the BHJ layer …”

Hot Hydrocarbon‐Solvent Slot‐Die Coating Enables High‐Efficiency Organic Solar Cells with Temperature‐Dependent Aggregation Behavior

“…Besides, due to the limited number of fundamental studies, today the strategy of morphology optimization during slot‐die coating with halogenated solvents is not sufficiently developed, which hinders the improvement of the device performance. [ 30,31 ] Moreover, when halogenated solvents are replaced with hydrocarbon solvents, the film morphology becomes more difficult to be controlled. Therefore, new insights are required to improve the morphology and performance of slot‐die coated OSCs processed from hydrocarbon solvents.…”

Recent Progress and Challenges toward Highly Stable Nonfullerene Acceptor‐Based Organic Solar Cells

“…[ 156 ] Based on the studies to date, it seems that the device optimization process through the printing process needs to be finely adjusted according to the molecular structure and the properties of the photoactive blends. [ 157–161 ]…”