NYCU initiates research on organic photovoltaic to improve efficiency


Taiwan’s Legislative Yuan passed a draft amendment to the Renewable Energy Development Act in 2023, requiring new buildings, expanded, or altered construction that meet certain conditions to install rooftop solar panels with a specific capacity to boost renewables.

While the draft amendment could drive Taiwan's solar energy generation, it presents a problem for rooftop gardening, as the current crystalline solar panels obstruct the sunlight necessary for plants and affect their growth, putting homeowners in a dilemma between installing solar panels and rooftop gardening.

How can solar energy and plants thrive together while increasing rooftop utilization? The answer lies in the organic photovoltaic (OPV) installations.

According to Professor Meng Hsin-fei (孟心飛) at the Institute of Physics of the National Yang Ming Chiao Tung University (NYCU), traditional crystalline solar panels are like thick slices of toast, with strong shading properties and an inability to transmit light. Organic solar panels, on the other hand, have a transmittance of around 10-30%.  While OPV’s generation efficiency is not comparable to that of crystalline ones, it offers value-added utilization of composite land use.

Different from the traditional crystalline solar panels that are produced by vaporizing atoms in a vacuum chamber at high temperatures and then grown into crystalline ingot before cutting, organic solar panels involve coating organic materials onto glass substrates, allowing them to dry and form a thin film, which constitutes an organic semiconductor. Compared with crystalline silicon, the organic semiconductor not only generates positive and negative charges and current under light but also offers better transmittance when paired with semi-transparent thin-film metal electrodes.

A research team led by Meng and Chao Yu-chiang (趙宇強) at the National Taiwan Normal University (NTNU) has conducted a demonstrative application at the Wufeng Agricultural Experimental Station, where they confirmed that under the coverage of over 20 organic solar panels, vegetables can still receive sufficient sunlight for growth. 

Additionally, Meng collaborated with the Environmental Engineering Institute's Professor Kao Cheng-chung (高正忠) on the "Green Roof Demonstration" project,  installing over 20 organic solar panels on the roof of the institute’s building and developed the "DIYGreen Zero-Wasted Circular Roof Farm" below to generate benefits of power generation and agricultural purposes.

Enhancing efficiency and lifespan through unique technology

In addition to the demonstration project, Meng and Chao have engaged in researching organic photovoltaic components, modules, and processing techniques in recent years in the hope to enhance the power generation efficiency and lifespan of large-area organic photovoltaic modules. 

"With our innovative coating process and module design, we've boosted the efficiency for A4-sized glass substrates from 5% to 11%. The estimated outdoor lifespan is three to four years, surpassing international research standards," Meng claimed.

In terms of efficiency, the organic solution applied to the surface of a glass substrate must be thin and uniform to achieve high efficiency. However, the conventional slot-die coating method used on large-area substrates involves squeezing the organic solution out through narrow gaps under pressure, which comes with drawbacks such as difficulty in precisely controlling the rate and complexity due to multiple pipelines. 

In contrast, the technique employed by Meng’s team, known as the scraping-coating process, involves dropping the solution with a fine needle at the base of a cylinder. By utilizing the principle of capillary action, the solution beneath the cylinder diffuses onto the substrate, enabling uniform coating in a simple, cost-effective, and non-precision-controlled manner.

As for lifespan, Meng’s team has improved the crystallization of organic materials through material combinations and designs to address the issue of organic material crystallization and film damage caused by ultraviolet rays in sunlight. This accomplishment has significantly elevated the stability of organic photovoltaic modules for outdoor operation, extending the outdoor lifespan to three to four years, surpassing all the currently published international literature.

Given Taiwan’s limited land area, restricting land to a single use may lead to various industries competing for land resources. Therefore, promoting multifunctional land use to enhance land efficiency is a more suitable solution for Taiwan. Organic photovoltaics not only can satisfy the needs of power generation and agriculture but also align with the current trend of agrivoltaics. This approach helps avoid controversies over "land use in the name of farming," improves crop quality problems caused by uneven sunlight, and ultimately, accelerates the solar deployment in Taiwan.

This article was originally published on Sci-Tech Vista. Read the original article.

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