Sup3 - Polymer solar cells - UCSD NANO 134 - Darren Lipomi

The speaker starts by greeting the audience and noting the attendance, then introduces the topic of polymers in solar cells. They explain that the focus is on polymers with semiconductor properties, such as fluorescence and charge transport, which are comparable to amorphous silicon. The potential of these materials to be printed like newspapers to create electronic devices is highlighted. The speaker also discusses the importance of solar energy, emphasizing the vast amount of energy from sunlight available compared to human consumption, and the need for clean energy production. The talk concludes with a comparison of land area requirements for different renewable energy sources, pointing out that solar energy is more efficient in terms of land use than others like wind or hydroelectric power.

This paragraph delves into the statistics of energy consumption in the United States, highlighting the dominance of petroleum, coal, and natural gas. The speaker points out the minimal contribution of solar energy at the time but notes a significant increase in solar's share by 2013. They also mention the wastage of energy due to inefficiencies in transportation and electricity generation. The discussion then shifts to the potential of solar energy, comparing the land area required for solar panels to existing land uses like highways, and setting a goal for solar energy cost-efficiency by comparing it to the cost of paint.

The speaker discusses the characteristics of organic solar cells, contrasting them with inorganic solar cells. They explain the concepts of p-type and n-type materials and how they create an electric field at the junction, which is crucial for the photovoltaic effect. The paragraph also covers the structure of organic solar cells, including the active layer made of polymers and fullerenes, and the importance of the phase separation between these materials for efficient charge separation and transport. The speaker emphasizes the flexibility and potential of organic solar cells, mentioning their low cost and the possibility of roll-to-roll manufacturing.

In this paragraph, the speaker focuses on the efficiency and cost aspects of solar energy, particularly organic solar cells. They mention the efficiency of solar cells made from certain materials and the potential for even higher efficiency with better materials. The speaker also discusses the cost of these materials in bulk and how they compare to the cost of paint, highlighting the economic feasibility of organic solar cells. Additionally, they touch upon the mechanical compliance and thinness of these cells, which allow for flexible and wearable applications.

The speaker introduces more advanced materials for organic solar cells, such as polythiophene and fullerene derivatives, which can be combined to create a photovoltaic effect. They explain the process of creating a bulk heterojunction by casting a film from these materials, which self-assembles into domains that facilitate charge separation. The importance of phase separation and molecular packing for device efficiency is emphasized, along with the challenges of exciton diffusion length relative to the material's light absorption length.

This paragraph explores the phase behavior of materials in organic solar cells and its impact on efficiency. The speaker discusses the need for a balance between phase separation and connectivity for efficient charge transport. They use the Goldilocks zone analogy to describe the ideal state for material mixing, where crystallites and amorphous domains interact to maximize charge separation without impeding exciton reach to the interface. The paragraph also touches on the diffusion of fullerenes into amorphous domains of polymers and its implications for device efficiency.

The speaker discusses the methods used to study the microstructure of organic solar cell materials, such as grazing incidence x-ray diffraction and atomic force microscopy. They explain how these techniques reveal the organization of polymer chains and the formation of crystalline domains, which are critical for understanding charge separation and transport. The importance of molecular architecture in achieving the desired microstructure for efficient solar cells is also highlighted, with examples of block copolymers and their potential to improve performance.

In this paragraph, the speaker provides an update on the state of organic solar cell technology, including the development of roll-to-roll fabrication and the deployment of solar parks. They describe the energy payback time for organic solar cells, which is significantly shorter than that of silicon photovoltaics, indicating the technology's sustainability. The speaker also mentions the practical aspects of deploying these solar cells in real-world environments and the challenges they may face, such as damage from environmental factors.

The speaker concludes by discussing the safety and practicality of organic solar cells, noting their potential to deliver high currents under certain conditions. They humorously caution about the unexpected dangers of touching the ends of a large solar cell array on a sunny day. The speaker also comments on the ease of repairing these solar cells, which can be cut and replaced as needed. Finally, they express anticipation for the next lecture in the series.