A research team of China's Nankai University has raised the conversion rate of organic PV cell to 17.3% recently, asserting possibility of breaking 20%, compared with previous record of 15% just achieved in April.
In recent years, scientists have been conducting research on new high-efficient, low-cost, and nontoxic PV power technology, as conversion rate of existing silicon PV cells, with 20-25 years of life, has stagnated at 15-22% and breakthrough appears to be unlikely.
One candidate is organic PV cell, made of organic materials partially or entirely, which can be solved in ink before being used in spraying or printing in manufacturing. With soft and pliable materials, organic PV cells may cost lower than silicon PV cells and may even be attached to clothes, windows, or autos.
Organic PV cells, however, are confronted with the problems of low conversion rate and instability. A breakthrough was achieved in April, when a research team of the University of Michigan unveiled an organic PV cell, with conversion rate reaching 15%, compared with existing 11-12%, and product life 20 year.
It is estimated that at 15% conversion rate and 20-year product life, PV power will cost only US$0.07 per kilowatt/hour, compared with existing average power rate of US$0.105 in the U.S., underscoring its huge cost advantage potential.
The Nankang University team blames low conversion rate of existing PV cells on "loose structure of the molecules of materials," believing that low electronics mobility would restrict the thickness of active layers, blocking effective utilization of sunshine. The team solves the problem by concatenating two layers with different organic materials, an arrangement which can also utilize sunshine more effectively and generate more power output, as the two layers with different materials can absorb light in different wave bands, according to Chen Yongsheng, director of nano-science and technology research center of the university.
Usage of combination materials for supplementary absorption of light has become a trend, such as absorption of light in 300-720 nm wavelength by one material and of light in 720-1,000 nm wavelength by another. Some team combines silicon with perovskite, with the former responsible for converting red light and near-red light into power and the latter for converting green light and blue light into power.
The Nankai team notes that it is possible to raise the conversion rate of its organic PV cell to over 20%, while pointing to its stability, as its efficiency dropped by only 4% after 166 days of testing.
The team is upbeat about the potential of organic PV power, saying the commercialization of its technology is around the corner. Chen Yong-sheng compares organic PV power to OLED, saying that both employ roughly similar materials and similar principle of physics, only with different direction, as one converts solar energy into power and the other converts power into light.
With OLED having been extensively applied in mobile phones and high-tier TV, Cheng Yongsheng believes that organic PV power may be commercialized in five years. The research result has been published in "Science."
(Written by Daisy Chuang, first photo courtesy of ESA_events via Flickr CC BY-SA 2.0)
