Publication date: 11th March 2026
Organic solar cells (OSCs) have achieved a remarkable increase in power conversion efficiency (PCE) in recent years, primarily driven by the development of new non-fullerene acceptor materials. Despite this progress, device stability remains a major challenge to commercialization. A significant performance degradation occurs during the initial hours of operation, known as burn-in loss. This effect is commonly attributed to morphological instabilities in the active layer. In contrast, our work demonstrates that the hole transport material plays a key role in enhancing the photo-stability and can effectively prevent our PM6:Y6 BHJ OSCs from the initial burn-in.
We investigated several hole transport materials, including PEDOT:PSS 4083, PEDOT:PSS pH-neutral, 2PACz, and corresponding bilayer modifications. Although pH-neutral PEDOT:PSS was explored as a non-acidic alternative to conventional PEDOT:PSS 4083, it failed to deliver comparable efficiency and stability. Therefore, we focused on the self-assembling molecule (2-(9H-carbazol-9-yl)ethyl)phosphonic acid (2PACz). Devices employing either PEDOT:PSS or 2-PACz as single HTLs exhibited pronounced photo-instability, retaining only 80% of their initial PCE (t80) after two and one day of illumination, respectively. In contrast, solar cells with PEDOT:PSS/2PACz bilayer HTLs deliver PCEs comparable to those of the individual HTLs, while effectively suppressing the initial burn-in. We achieved highly photo-stable PM6:Y6 OSCs, with virtually no PCE loss over 27 days (650 h) of continuous illumination.
To further elucidate the degradation mechanisms in the investigated OSC architectures, we employed transient photovoltage measurements. These results revealed that the improved stability of the devices with bilayer HTL structure stems from less pronounced interfacial disorder induced during photo-aging. Overall, our results demonstrate that, rather than replacing PEDOT:PSS entirely, interfacial passivation with 2PACz provides an effective strategy to improve the photostability of high-performance OSCs.
Hönigsberger, J.; Rajan, L.; Pavlica, E.; Troi, L.; Binter, K.; Trimmel, G.; Rath, T. Enhanced Photostability and Burn-In Suppression in Organic Solar Cells via a 2PACz-Modified PEDOT:PSS Hole Transport Layer; manuscript submitted, 2026.
Financial support of this study by the Austrian Science Fund (FWF) and the alpha+ Stiftung under grant number 10.55776/P36671 is gratefully acknowledged.
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