3D Nanoscale Morphology Characterization of Ternary Organic Solar Cells

Abstract

It is highly desired to develop advanced characterization techniques to explore the 3D nanoscale morphology of the complicated blend film of ternary organic solar cells (OSCs). Here, ternary OSCs are constructed by incorporating the nonfullerene acceptor perylenediimide (PDI)‐diketopyrrolopyrrole (DPP)‐PDI and their morphology is characterized in depth to understand the performance variation. In particular, photoinduced force microscopy (PiFM) coupled with infrared laser spectroscopy is conducted to qualitatively study the distribution of donor and acceptors in the blend film by chemical identification and to quantitatively probe the segmentation of domains and the domain size distribution after PDI‐DPP‐PDI acceptor incorporation by PiFM imaging and data processing. In addition, the energy‐filtered transmission electron microscopy with energy loss spectra is utilized to visualize the nanoscale morphology of ultrathin cross‐sections in the configuration of the real ternary device for the first time in the field of photovoltaics. These measurements allow to “view” the surface and cross‐sectional morphology and provide strong evidence that the PDI‐DPP‐PDI acceptor can suppress the aggregation of the fullerene molecules and generate the homogenous morphology with a higher‐level of the molecularly mixed phase, which can prevent the charge recombination and stabilize the morphology of photoactive layer.

Miscibility driven morphology modulation in ternary solar cells

“…To further explore the distribution and compatibility of materials in the active layer, advanced photo-induced force microscopy (PiFM) coupling AFM with infrared (IR) spectroscopy was used, allowing the characterization of the distribution of different components in the blend film with a high spatial resolution. 15 The topography images of the binary and ternary films (10%, 20% and 50% PDI-EH), and corresponding PiFM spectra are shown in Fig. S5 (ESI†).…”

“…When well designed, they can help adjust the miscibility of host D/A materials for regulation of the phase separation at the nanoscale, and moreover, extend the spectral absorption for harvesting more photons and form the cascade-structural energy levels for efficient charge transfer. 13–15…”

“…When well designed, they can help adjust the miscibility of host D/A materials for regulation of the phase separation at the nanoscale, and moreover, extend the spectral absorption for harvesting more photons and form the cascadestructural energy levels for efficient charge transfer. [13][14][15] In this work, we chose a PBDB-T donor and ITIC-4F acceptor (Fig. 1a) to serve as host photoactive layer materials in ternary OSCs due to their extraordinary photo-stability approaching 10 years.…”

Achieving high performance organic solar cells with a closer π–π distance in branched alkyl-chain acceptors

“…To achieve ideal charge transportation, the solubility and the interaction of NFA molecules and the morphology 36,37 of blends with donor materials should be maximized for improved photovoltaic properties. From the perspective of molecular design and its modification, changes in the side chains 35,38–41 of acceptors are among the most convenient and efficient methods to regulate the packing modes and solubility of molecules.…”

“…As a result, one of the most important items in current research is deep exploration of the potential of OSCs with a view to achieving better performance through the optimization of materials. [31][32][33][34][35] To achieve ideal charge transportation, the solubility and the interaction of NFA molecules and the morphology 36,37 of blends with donor materials should be maximized for improved photovoltaic properties. From the perspective of molecular design and its modication, changes in the side chains 35,[38][39][40][41] of acceptors are among the most convenient and efficient methods to regulate the packing modes and solubility of molecules.…”