A pinboard by
Konrad Domanski

I am PhD student at EPFL, Switzerland working on a new generation of solar cells.


I am making perovskite solar cells stable to make them commercially attractive.

Perovskite solar cells (PSCs) have attracted a substantial interest owing to a very fast achievement of efficiencies >20 % within only several years of development. However, for any solar cell to become technologically viable, two additional milestones have to be achieved alongside high efficiency: means of industrial production and good operational stability. The former being mostly the focus of private sector, understanding degradation and improving the stability of PSCs has become the main research topic in the field of emerging photovoltaics. During my PhD, I first designed and built a dedicated setup to investigate stability of PSCs. Subsequently, I described the intrinsic instability of state-of-the-art PSCs and I showed how through incorporation of Cs into perovskite breakthrough room-temperature stability coupled with record efficiency can be achieved. Later, I discovered however, that these solar cells suffer from irreversible degradation if left at elevated temperatures. This is due to a vulnerability to Au diffusion from the electrode. I discovered, that by using a Cr diffusion barrier, one can circumvent this problem (albeit at considerable efficiency loss). Subsequently, I described an alternative solution to the same problem by using a polymeric hole transporting layer. This approach effectively stops Au diffusion without compromising device efficiency. Finally, I found a third approach: replacing the expensive Au electrode with one based on carbon nanotubes. In parallel, I also explained how mobile ions in the perovskite lead to a partial reversibility of losses in aged devices. This has far-reaching consequences for the way stability measurements of PSCs are conducted and how their lifetime is reported. Most recently, I described how different factors such as temperature, illumination, atmosphere and load on the device affect the stability of PSCs. Based on this, I recommend PSC stability measurement protocols as the first attempt to bring the community to a consensus on how to age PSCs. This is needed to streamline the efforts to create stable PSCs and to commercialize the technology.


Migration of cations induces reversible performance losses over day/night cycling in perovskite solar cells

Abstract: Perovskites have been demonstrated in solar cells with a power conversion efficiency of well above 20%, which makes them one of the strongest contenders for next generation photovoltaics. While there are no concerns about their efficiency, very little is known about their stability under illumination and load. Ionic defects and their migration in the perovskite crystal lattice are some of the most alarming sources of degradation, which can potentially prevent the commercialization of perovskite solar cells (PSCs). In this work, we provide direct evidence of electric field-induced ionic defect migration and we isolate their effect on the long-term performance of state-of-the-art devices. Supported by modelling, we demonstrate that ionic defects, migrating on timescales significantly longer (above 103 s) than what has so far been explored (from 10−1 to 102 s), abate the initial efficiency by 10–15% after several hours of operation at the maximum power point. Though these losses are not negligible, we prove that the initial efficiency is fully recovered when leaving the device in the dark for a comparable amount of time. We verified this behaviour over several cycles resembling day/night phases, thus probing the stability of PSCs under native working conditions. This unusual behaviour reveals that research and industrial standards currently in use to assess the performance and the stability of solar cells need to be adjusted for PSCs. Our work paves the way for much needed new testing protocols and figures of merit specifically designed for PSCs.

Pub.: 10 Jan '17, Pinned: 25 Aug '17