Programm

With the increase of power conversion efficiency (PCE), the stability of organic solar cells becomes the biggest obstacle for their commercialization. Nanomorphology of the bulk-heterojunction layer (BHJ) plays an important role in determining the performance and stability of the cells. In addition to pure donor and acceptor phases, amorphous intermixing phases of the donor and acceptor molecules are also formed within the BHJ film. However, quantitatively determining the content and structure of the intermixing phase is quite challenging. In this presentation, we demonstrate a method to characterize the aggregation and composition of non-fullerene acceptors (NFA) in the intermixed phases. By measuring the absorption spectrum of the blend films with different NFA concentration, we found a red-shift of the maximum absorption wavelength with the increase of the NFA concentration, which is ascribed to the change of intermolecular interactions. With these results, we can identify the nanostructure of the BHJ films under different processing conditions, and the results are correlated to the device efficiencies. Also, we found that the structure of the intermixing amorphous phases is rather stable under light and thermal stress, demonstrating an excellent intrinsic stability of the organic solar cells.

Talk will provide an update on the NREL perspective on metal halide perovskite (MHP) based photovoltaics (PVs).  This will include an argument of why MHP-PV technologies are critical and how the need to develop these technologies drives research needs in stability and reliability.  Results from across multiple studies undertaken at NREL will be summarized to identify both technical success and failures or missed opportunities to advance the stability of MHP and MHP enabled PV technologies.  Connections to device efficiency and manufacturing which are intimately linked to stability and reliability will also be highlighted.

Organic solar cells have recently reached power conversion efficiencies of over 19%, highlighting the stability as their last remaining weak point. Their organic nature makes them strongly influenced by stresses such as oxygen, light, heat and humidity, which can be commonly found in their working environment. 

Incorporation of stabilizing additives (antioxidants, radical scavengers, hydroperoxide decomposers, UV absorbers) in active layers of organic solar cells is an attractive approach for inhibiting degradation as it is both inexpensive and easily upscalable, and it does not introduce further complexity into the device architecture.

Here we present our recent results on long-term stability improvement using naturally occurring antioxidants, such as vitamin C and beta-carotene, that act as singlet oxygen quenchers and radical scavenging compounds, as well as explore the synergistic effects of such compounds on the mechanical properties. The reported results and methods indicate a desirable route for mitigating degradation in organic solar cells.

References

1. Atajanov R, Turkovic V et al.  The mechanisms of degradation and stabilization of high-performing non-fullerene acceptor based organic solar cells. (in preparation)

2. Balasubramanian S, Turkovic V et al. Vitamin C for Photo-Stable Non-fullerene-acceptor-Based Organic Solar Cells. ACS Appl Mater Interfaces 2021; dx.doi.org/10.1021/acsami.3c06321

3. Prete M, Turkovic V et al. Synergistic effect of carotenoid and silicone-based additives for photooxidatively stable organic solar cells with enhanced elasticity. J Mater Chem C 2021; dx.doi.org/10.1039/D1TC01544C 

4. Turkovic V et al. Biomimetic Approach to Inhibition of Photooxidation in Organic Solar Cells Using Beta-Carotene as an Additive. ACS Appl Mater Interfaces 2019; dx.doi.org/10.1021/acsami.9b13085

5. Bregnhøj M, Turkovic V et al. Oxygen-dependent photophysics and photochemistry of prototypical compounds for organic photovoltaics: inhibiting degradation initiated by singlet oxygen at a molecular level. Methods Appl Fluoresc 2019; dx.doi.org/10.1088/2050-6120/ab4edc