Researchers have now developed semitransparent organic photovoltaic cells with high flexibility and durability for seamless integration into various surfaces. 

Organic photovoltaics (OPVs) as lightweight, transparent, and thin solar cells are promising for the generation of electricity from sunlight. Such cells can transform surfaces like windows and roofs into self-sustaining power sources. Recently, researchers have made significant strides in enhancing OPVs, making them strain-durable and ultra-flexible. This breakthrough can open the doors to a wide range of applications, including the integration of solar power generation into windows, Internet of Things devices, clothing, and more.

Organic photovoltaics (OPVs) are lightweight, transparent, and flexible, making them suitable for seamless and aesthetic integration into various surfaces for electricity generation, including windows and wearable devices. 

Image courtesy: Lee, Hanbee, et al. "Ultra-flexible semitransparent organic photovoltaics." npj Flexible Electronics 7.1 (2023): 27.

Solar energy is undoubtedly an abundant source of energy, but its potential is far from being fully harnessed. Currently, most solar cells are installed in large, flat areas like rooftops or solar farms due to their low flexibility and transparency.  An emerging class of transparent, lightweight, ultrathin, and flexible solar cells known as organic photovoltaics (OPVs) is revolutionizing the way in which electricity is generated for powering our daily needs, overcoming the limits of surface area and flexion. These advanced solar cells can be integrated into windows, Internet of Things devices, and even clothing, turning these surfaces into self-sustaining sources of power, with the ability to generate electricity from sunlight.

However, they are far from being ideal. There is an intrinsic trade-off between power conversion efficiency (PCE) and average visible transmittance (AVT), which limits the performance of these OPVs. Furthermore, the inherent brittleness of traditional transparent electrodes such as indium tin oxide challenges their durability and makes it difficult to achieve ultra-flexibility, amidst extreme repetitive mechanical stress and optical transparency, simultaneously. Therefore, significant research efforts are underway to overcome these challenges and make the OPVs more durable, efficient, and transparent for advancing their use. 

Advancing research in this direction, a new study published in npj Flexible Electronics on 3 June 2023 by an international team of researchers led by Assistant Professor Sungjun Park and Associate Professor Jong H. Kim from Ajou University, Republic of Korea, has now proposed OPVs with thinner, ultra-flexible, and semitransparent electrode materials, named “semitransparent organic photovoltaics” (or ST-OPVs). 

The ST-OPVs proposed in this study have a thickness below two micrometers, are fabricated on a parylene/SU-8 substrate, and utilize an ultrathin silver (Ag) bottom electrode and a dielectric/metal/dielectric (DMD) top electrode. The DMD structure, consisting of molybdenum trioxide (MoO₃)/Ag/MoO₃ layers, offers excellent optical transparency. Thanks to their nanometer-scale thickness, the ultrathin electrodes impart the proposed OPVs remarkable durability, transparency, and ultra-flexibility. 

On testing their optical and electrical performance, the OPV devices retained 73% of their initial efficiency after undergoing 1000 compression–release cycles at a compressive strain of 66%. Moreover, the average visible light transmittances remained above 30%. 

Elaborating further on this, Dr. Kim says, “Notably, the ST-OPVs developed by us achieved a peak PCE of 6.93% and an AVT exceeding 30%, pointing to their high performance. Moreover, to the best of our knowledge, the unprecedented flexibility displayed by these OPVs represents the highest performance reported thus far.” 

These characteristics make the proposed ST-OPVs suitable for integration into a wide variety of surfaces, without compromising the overall functionality or aesthetics. For instance, they could be utilized for designing windows that are a blend of utility and design and can generate electricity. Moreover, they could be incorporated into wearable devices to serve as a reliable and convenient source of power generation for these devices. “In the long-term, the practical implementation of our devices could significantly enhance energy generation in diverse settings, right from buildings to human bodies. This, in turn, can contribute to the fulfillment of the daily-life energy needs of people while maintaining environmental and personal well-being,” concludes Prof. Park. 

Reference

*Corresponding authors’ emails: jonghkim@ajou.ac.kr (Jong H. Kim); leesh23@kongju.ac.kr (Seung-Hoon Lee); sj0223park@ajou.ac.kr  (Sungjun Park)

About Ajou University

Founded in 1973, Ajou University has quickly grown to become one of the top universities in the Republic of Korea. With over 15,000 students and 50 research centers in diverse fields, Ajou University partakes in the largest national research and graduate education project funded by the Korean Ministry of Education. In line with its recently reformed vision, Ajou University’s goal is to change society by connecting minds and carrying out high-impact research to improve the welfare of people in and outside Korea. 

Website: https://www.ajou.ac.kr/en/index.do 

About Dr. Sungjun Park and Prof. Jong H. Kim 

Sungjun Park is an Assistant Professor in the Department of Electrical and Computer Engineering and Jong H. Kim is an Associate Professor in the Department of Molecular Science and Technology at Ajou University, Republic of Korea. Their research focuses on the development of novel solution-processed organic and hybrid optoelectronics materials and soft electronic devices and their integration into wearable sensors and biomedical applications. Dr. Park can be reached by email at sj0223park@ajou.ac.kr, and Dr. Kim can be reached by email at jonghkim@ajou.ac.kr.