Recent advances in solar cell technology have unveiled the potential of non-fullerene acceptors (NFAS) as alternatives to traditional fullerene-based materials, which have faced issues with efficiency and stability. A research team led by scientists from the City University of Hong Kong has developed two novel Y-type NFAS, namely Y-Phen and Y-CE, capable of significantly enhancing the performance of inverted perovskite solar cells (PSCs). This study outlines how these modified materials can lead to notable improvements in carrier transport dynamics and operational longevity.
Metal halide perovskite solar cells have drawn considerable attention for their high conversion efficiencies and the versatility of their materials. Already, PSCs have showcased power conversion efficiencies (PCEs) above 26%. Yet, the electron-transporting layers (ETLs) remaining integral to device performance have not received the same level of focus. The function of the ETL is pivotal, as it must provide efficient electron transport, suitable energy levels for interfacial alignment, and maintain compatibility with the perovskite layer to optimize charge transfer.
For years, fullerenes and their derivatives were favored for their suitable electronic properties. Nevertheless, they face significant drawbacks, including energy disorder and poor long-term stability under thermal stress. To overcome these challenges, the research team looked beyond fullerenes, developing NFAS which not only present higher-performance traits but also promise enhanced structural stability.
Enter Y-Phen and Y-CE, two newly synthesized NFAS where structural modifications have been made to the typical benzothiadiazole core. These changes include the integration of phenanthroline and crown ether, aimed at enhancing molecular dipoles and ensuring ordered molecular assembly. By tapping these strong supramolecular interactions, the research aims to optimize the performance of inverted PSCs. Testing revealed significant improvements, with Y-CE achieving the highest certified PCE of 25.59%—among the best reported data for cases utilizing NFAS.
The importance of energy level alignment at the perovskite-NFA interface was highlighted as the team conducted density functional theory (DFT) calculations confirming the improved molecular orientation and interactions. Unlike fullerenes, the newly developed NFAS adhered to the perovskite surfaces more effectively, facilitating improved energy level alignment and minimizing interfacial energy disorders.
More compelling is the operational longevity of these devices; experiments indicate Y-CE and Y-Phen maintain over 90% of their initial PCE after extensive thermal aging under high temperatures, showcasing less than 10% degradation after 1440 hours, vastly outpacing their fullerene counterparts, which reported declines of up to 20% under similar conditions.
The results clearly indicate the promising direction of utilizing NFAS as ETLs, also supported by their lower carrier accumulation rates and enhanced charge transport properties pivotal for improving operational performance. Details from the experiments show the Y-CE NFA produces considerable quenching of photoluminescence from the perovskite layer, signifying efficient charge transfer dynamics which are imperative for high-performing solar cells.
Conclusive findings from this research highlight the path forward for perovskite solar cell technology. By leveraging the properties of non-fullerene acceptors, particularly those enhanced by molecular modifications, future solar cells can expect not just improved efficiency but stabilization against the environmental conditions affecting performance longevity.
With the potential for rapid industrial adaptation of these new NFAS, this study provides invaluable insights for future research and development within solar technology fields, marking advancements not just for academic inquiry but real-world applications aiming toward sustainable energy solutions.