In a study recently published in Sustainable Energy Fuels, researchers from the Palomares group at the BIST centre ICIQ and the NanoElectronic and Photonic Systems research group (NEPHOS) at the URV use organic semiconductor materials such as plastic polymer and small molecules to convert solar irradiation into electricity in organic solar cells.
Over the last few years, organic solar cell technology has reached a significant milestone towards commercialisation by exceeding 10% efficiency (the parameter that calculates the portion of solar irradiation that can be converted into electricity by the photovoltaic effect) and is now getting closer to 20% efficiency. The emergence of organic solar cells has attracted tremendous attention in scientific and industrial communities due to their potential properties including semi-transparency, flexibility, environmental-friendliness, solution-processability, light-weight, low-cost, and scalability for roll-to-roll manufacturing. However, high efficiency and low-cost are not the only requirements for scaling up the organic solar cell into the market.
The main objective pursued by the scientists of the present work was to make organic solar cells more durable, and increase their lifespan so that they can be produced at a commercial scale. The research team performed a stability study of organic solar cells in accordance with the internationally agreed-upon ISOS stability protocol to understand the degradation mechanism. Their objective was to find strategies to make the shelf-lifetime of this technology longer – especially while the device is stored.
Since the degradation mechanism in organic solar cells is thoroughly complex, the simple and commonly used electrical characterisation of current density-voltage measurement was not enough to provide solid information to understand the dominating mechanism of performance degradation.
This study represents a novelty in its field since the authors have combined for the first time two powerful techniques of impedance spectroscopy and transient photovoltage/photocurrent measurement to study shelf-lifetime degradation. Additionally, the ISOS-D1 protocol was applied to organic solar cells under different environments to quantify the lifetime and stability, and identify the predominant degradation mechanisms within it. They also performed an inverted strategy and compared three different electron transport layers to understand which one is the best strategy for improving the shelf-lifetime of organic solar cells. The findings of the work suggest that the main cause for the degradation of the organic solar cells is the formation of darkness traps in the interface of the device, and air exposure.
Learn more on the ICIQ website.