Interdigitated Interfaces: Paving the Path to Ultra-Efficient Perovskite/Organic Solar Cells

Integrated perovskite/organic solar cells (IPOSCs) represent an advanced approach in the field of photovoltaic technology. They combine the advantage of high efficiency of perovskite solar cells with the flexibility and tunable properties of organic photovoltaics which will result in enhanced overall device performance, stability, and potentially reducing fabrication costs. Indeed, perovskite materials have gained significant attention due to their excellent light absorption properties, high charge carrier mobilities, and tunable bandgaps, which have led to rapid advancements in their efficiency, achieving power conversion efficiencies (PCEs) comparable to or even surpassing those of traditional silicon-based solar cells. However, their long-term stability, toxicity of lead content, and sensitivity to environmental factors remain challenges. On the other hand, organic solar cells offer advantages in terms of mechanical flexibility, lightweight, and the potential for low-cost roll-to-roll manufacturing processes. Their tunable electronic and optical properties through molecular design also present a unique advantage. Despite these benefits, organic solar cells generally exhibit lower efficiencies and stability compared to their inorganic counterparts

A key challenge in perovskite solar cells is their limited absorption range, primarily confined to the visible spectrum, thus not fully exploiting the near-infrared (NIR) region of solar radiation. To addresses this limitation, a new study published in ACS Applied Materials & Interfaces by PhD candidate Yanliang Liu, Professor Sung Heum Park, and Professor Junghwan Kim from the Institute of Energy Transport and Fusion Research at Pukyong National University in South Korea, the authors focused on the development and optimization of IPOSCs to enhance their PCE. The core objective was to extend the absorption spectrum of these solar cells into the NIR range, thereby utilizing a broader range of the solar spectrum for energy conversion. This was accomplished by integrating perovskite materials with bulk heterojunction (BHJ) organic films, each known for their favorable photovoltaic properties.

The researchers designed a novel architectural feature for IPOSCs by forming interdigitated interfaces between the perovskite and BHJ layers. This design significantly increases the contact area between these layers, facilitating enhanced charge transfer. The interdigitated interface is achieved by allowing large microscale perovskite grains to form, into which the BHJ materials can infiltrate along the grain boundaries. This not only improves the interface area but also ensures more efficient charge separation and collection. The team optimized the crystallinity of the perovskite layer and the nanomorphology of the BHJ layer. The perovskite layer’s crystallinity was enhanced to produce large grains that favor the formation of the interdigitated structure. Meanwhile, the morphology of the BHJ layer was optimized to ensure efficient charge transport and collection, contributing to the overall efficiency of the solar cells. One of the landmark achievements of the research team is the realization of a PCE of 18.43% in the P−I−N-type IPOSCs. This high efficiency is attributed to the synergistic effects of the interdigitated interface and the optimized BHJ nanomorphology. The interdigitated design facilitates efficient charge transfer, while the optimized BHJ layer ensures effective charge transport and collection.

According to the authors, by integrating perovskite with NIR-absorbing BHJ organic films, the absorption spectrum of the solar cells was extended into the NIR range. This is crucial for harnessing a larger portion of the solar spectrum, particularly the NIR light, which conventional solar cells often do not utilize effectively. Additionally, the authors introduced the merged annealing method which is instrumental in achieving the desired perovskite crystallinity and the interdigitated interface. The newly proposed fabrication method results in enlarging the perovskite grains and the gaps between them, facilitating the infiltration of BHJ materials and the formation of the interdigitated structure.

The study’s findings have significant implications for the field of photovoltaics, offering a new pathway to design and fabricate high-efficiency solar cells that can harness a broader spectrum of solar radiation. The interdigitated interface design, in particular, presents a novel approach to enhancing charge transfer efficiency in solar cells, which could be applicable to other types of photovoltaic devices as well. In conclusion, the work of Liu, Park, and Kim represents a significant advancement in the development of high-efficiency IPOSCs. The new innovative approach to designing IPOSCs,  successfully sets a new benchmark for the efficiency of hybrid perovskite-organic solar cells. The new study not only contributes to the fundamental understanding of charge transfer mechanisms in IPOSCs but also opens up new avenues for the development of high-efficiency solar cells capable of harnessing a broader spectrum of solar radiation.