Crystallinity and Orientation Manipulation of Anthracene Diimide Polymers for All‐Polymer Solar Cells

Abstract

Electron-carrying polymers are highly desired for various optoelectronic applications but are still scarce. Herein, two anthracene diimide (ADI) polymers with thiophene and bithiophene as comonomer, respectively, are reported as electron acceptor materials in all-polymer solar cells (all-PSCs) for the first time. Effects of crystallinity and orientation of two polymer films as well as their blends with different donor polymers on photovoltaic properties are elaborately investigated by grazing-incidence X-ray diffraction and photo-induced force microscopy. It is found that molecular crystallinity and orientation determine the blend film morphology, and the similar high crystallinity and the same faceon orientation of donor and acceptor polymers are favorable for obtaining excellent photovoltaic performances. With this principle, a suitable donor polymer is singled out to match with the ADI acceptor polymer, offering an impressive efficiency of ≈7% for all-PSCs. This work demonstrates that ADI polymers are promising as acceptor materials and provides guidelines for screening donor and acceptor polymer combinations for all-PSCs.

All-Polymer Solar Cells Incorporating Readily Accessible Naphthalene Diimide and Isoindigo Acceptor Polymers for Improved Light Harvesting

“…Note that r-PNIT has a lamellar spacing (23.47 Å) similar to that of PNIT , reflecting the identical alkyl substituents, but the corresponding CCL (61.20 Å) is significantly lower and the π–π distance/CCL (4.07/9.16 Å) is increased/reduced, respectively, demonstrating overall lower crystallinity vs PNIT . The π–π d -spacings for PNIT / r-PNIT are similar to those reported for PBNIID (3.8 Å), N2200 (4.11 Å), and PADIOD-2T (3.9 Å), while f-BTI2-FT has a closer π–π d -spacing (3.57 Å) likely reflecting the extended fused ring structure and thiophene fluorine substituents promoting π–π interactions. ,,, Additionally, PNIT exhibits a (200) peak in the OOP profile (0.523 Å –1 ), which is not observed for r-PNIT , and PNIT also has more ordered domains with preferential face-on orientations, while r-PNIT has a nearly complete crystallite rotational disorder. , A π-face-on morphology is desirable for organic photovoltaic (OPV) efficiency, such as in APSCs, where charge extraction should occur in the vertical direction. Note that PBDB-T:PNIT PBDB-T: / r-PNIT blend films have relatively similar lamellar spacings (22.20/22.21 Å), π–π distances (3.78/3.80 Å), and (010) CCLs (10.50/11.04 Å), respectively, reflecting the 2:1 mass ratio of PBDB-T: acceptor polymer.…”

“…GIWAXS diffraction patterns and related line-cut profiles for the out-of-plane (OOP) and in-plane (IP) reflections for the neat and blend films are provided in Figure 5 with quantitative data compiled in Table 3. For all polymer films, lamellar spacings (reflection = 100)/π−π distances 23,24,32,68 Additionally, PNIT exhibits a (200) peak in the OOP profile (0.523 Å −1 ), which is not observed for r-PNIT, and PNIT also has more ordered domains with preferential face-on orientations, while r-PNIT has a nearly complete crystallite rotational disorder. Film preparation is as described for APSC active layers.…”

“…This exemplary result demonstrates the utility of structurally simplistic acceptor polymers and highlights the importance of optimizing the pairing of the donor and acceptor polymers, the active layer morphology, and the device architecture. The success of N2200 has prompted the design and development of other structural analogs, such as PADIOD-T and f-BTI2-FT (Figure A), yielding APSC PCEs of 6.95 and 6.85%, respectively. , Although the PCEs for PADIOD-T and f-BTI2-FT are lower than those of PTzBI-Si:N2200 , these examples have not undergone an extensive optimization as N2200 , and they serve to demonstrate the utility of the diimide functional group for developing new polymer acceptors. Moreover, these polymers incorporate π-extended fused rings, which are an effective strategy for improving light harvesting and facilitating charge transport, but significantly enhance the synthetic complexity.…”

Understanding the molecular mechanisms of the differences in the efficiency and stability of all-polymer solar cells

“…Apart from the clear descriptions of structure-property relationships, 31,32 simultaneously achieving a highly efficient and stable BHJ microstructure is also particularly challenging for all-polymer systems because the reduced entropic contributions significantly suppress donor-acceptor (P D -P A ) pair miscibility. 6,[33][34][35] Although modifying film processing technologies (e.g. binary solvent mixtures and solid additives) to improve the P D -P A pair miscibility is a promising strategy, such approaches are highly empirical and system dependent, often providing limited performance benefits.…”

Structural Engineering of Anthracene Diimide Polymers for Molecular Ordering Manipulation

“…As their analogue, anthracene diimide (ADI) is also of great appeal because of its suitable electron affinity and extended conjugation along the equatorial direction but suffers from challenges in synthesis of its polymers. Very recently, we have successfully prepared two dibromide ADI monomers and their polymers and furthermore demonstrated the potential of ADI polymers as electron acceptors in organic photovoltaics. , However, studies on properties of the ADI polymer are still in their infancy, and especially how to manipulate molecular ordering of the newly developed ADI-based polymers, considerably correlating with the molecular packing property and charge transporting behavior which determine their performances in organic electronic devices, remains unknown.…”