First author: Youcai Liang, Difei Zhang
Computer author: Li Ning, Huang Fei
Communication unit: South China University of Technology
[Research Highlights]
The power conversion efficiency of organic solar cell (OSC) has reached more than 19%. However, jointly achieving high efficiency and long-term stability remains a huge challenge. Here, Y6-analyte and 2,2'-bithiophene monomers were used to construct a series of oligomer receptors to study the effects of molecular size and accumulation characteristics on the performance of photovoltaic . can change the thermal performance, crystallization behavior and molecular accumulation by changing the length of the molecular chain, and achieve the best microstructure and more stable morphology in blended films. Binary OSC based on oligomer receptors achieves an efficiency of more than 15% and an extrapolated T80 lifetime over 25000 h.
[Main content]
bulk heterojunction (BHJ) Organic solar cell (OSC) has attracted widespread research interest due to its huge advantages in dispersed photovoltaic applications, showing great potential to supplement traditional solar technology. In recent years, has undergone a revolution in power conversion efficiency (PCEs) of OSCs in recent years due to the rapid development of small molecule non-fullerene acceptors (SM-NFAs), which show infinite possibilities in molecular design, complementary absorption in the near-infrared region and appropriate energy levels of polymer donors. In particular, Y6 and its derivatives, as one of the most significant breakthroughs in SM-NFA, has increased the PCE of single-junction OSC to 19%. However, in order to achieve commercial products and applications, the broad prospects of PCE of OSCs should be accompanied by excellent stability. Although the efficiency of OSC based on Y6 and its analogs is very high, the inherent low glass transition temperature (Tg) and high diffusion properties of these Y series SM-NFAs are easy to form kinetic unstable morphology in the active layer of OSC, which is an obstacle to long-term stability.
To address the morphological instability of the BHJ active layer, a simple and elegant strategy is to construct polymer acceptors by polymerizing SM-NFA, which can inherit the advantages of the precursor SM-NFA, such as the high extinction coefficient in the near-infrared region, and a rather high electron mobility, increasing the PCE of all polymer solar cell (APSC) to about 17%. Although APSCs show better stability under thermal stress or light than SM-NFA-based OSCs, the properties of polymer acceptors depend in part on batch and molecular weight, which increases uncertainty in APSC device processing compared to system-based systems, limiting the development and commercialization of APSCs .
To avoid the inherent problems of SM-NFA and polymer receptors at the same time, it is very necessary to develop new materials with high Tg and a certain chemical structure . In polymer physics, it is generally believed that the extension of the molecular chain will limit the movement of the molecular chain, especially the low molecular weight oligomer . Therefore, the precisely defined oligomer is also expected to increase the Tg of SM-NFA and form a stable morphology in the active layer, determining the service life of the OSC. Although researchers reported over 10,000 h of OSCs for T80, it is still challenging to build OSCs that combine high efficiency and long life and meet practical application needs. Inevitably, there is some controversy over whether high efficiency and long-term stability can be achieved simultaneously.
Here, to evaluate the feasibility of designing stable and efficient OSCs with oligomer receptors and to understand the structural-functional relationship at the molecular level, an oligomer was synthesized by a one-pot reaction with Y6 analog (OY1) as monomer and 2,2'-bithiophene as π-bridge unit. When PBDB-T is used as the electron donor, the resulting oligomer acceptors OY2, OY3 and OY4 have an uncertain difference with their parent SM-NFA OY1 and the corresponding polymer acceptors (POYs) in terms of optical properties and photovoltaic properties. However, different thermal properties, crystallization behavior and molecular sorting were detected in NFAs with different molecular chain lengths. Thanks to precise adjustment of molecular size, OY3 combines sufficient crystallinity inherited from OY1 and thermal stability comparable to POY, thereby achieving an optimized microstructure and stable morphology in the corresponding blended films.Through the light stability test, OSC retains more than 90% of the initial PCE after running for more than 1000 h, and extrapolated T80 for more than 25000 h.
Figure 1. Material characterization of receptor
Table 1. Average OSC performance parameters of conventional devices based on different receptors mixed with PBDB-T
Figure 2. Device performance of OY1-OY4 and POY
Figure 3. Molecular stacking behavior and photophysical properties of OY1, OY3 and POY
Figure 4. Ni–Mo–Nb Stability evaluation of MGs
Figure 5. Advantages of OY3html
Literature information
Youcai Liang, Difei Zhang. et al. Organic solar cells using oligomer acceptors for improved stability and efficiency. Nature Energy (2022).
https://doi.org/10.1038/s41560-022-01155-x
