석상일 화학硏 박사팀, 세계 최고 효율 페로브스카이트 태양전지 개발 New ion continues perovskite solar’s flat-out progress
네이처지에 실려
5~10년 안에 상용화
석상일 한국화학연구원 박사팀은 가로세로 10cm 크기의 페로브스카이트 태양전지 모듈을 제작한 뒤 선풍기와
연결해 정상적으로 작동하는 것을 확인했다. - 한국화학연구원 제공
케이콘텐츠 kcontents
|
국내 연구진이 차세대 태양전지로 불리는 ‘페로브스카이트 태양전지’의 효율을 세계 최고 수준으로 끌어올리는 데 성공해 연구 결과를 과학 학술지 네이처 8일자에 발표했다.
왼쪽부터 석상일, 전남중, 노준홍 한국화학연구원 박사.
석상일 한국화학연구원 책임연구원은 7일 “지난해 논문 제출 당시 페로브스카이트 태양전지의 효율이 18.4%를 기록했다”며 “논문 게재 이후에도 효율을 계속 높여 현재 20.1%까지 올렸다”고 밝혔다.
이 기록은 미국 재생에너지연구소(NREL)에서 공인받은 것으로 페로브스카이트 태양전지 기술에서는 한국 연구진이 세계적으로 가장 앞서 있다. 태양전지 효율 이 20.1%라는 것은 태양에너지를 100으로 볼 때 이 가운데 20.1을 전기로 바꿀 수 있다는 것이다.
페로브스카이트는 전기 전도성이 뛰어난 결정 구조를 일컫는 말로 할로겐화 납, 메틸암모늄, 포름아미디늄 등 무기물과 유기물을 섞어 만든다. 얇은 필름 형태로 잘 휘어져 활용도가 뛰어난 것으로 평가받는다. 현재 가장 널리 쓰이는 실리콘 태양전지와 비교해 제작비는 3분의 1 수준이다.
또 실리콘에 페로브스카이트를 첨가하면 실리콘 태양전지의 효율을 5% 가까이 올릴 수 있고, 빛을 가했을 때 전기를 발생시키는 태양전지의 원리를 역으로 이용하면 페로브스카이트로 고효율 발광소자도 만들 수 있다.
특히 차세대 태양전지의 라이벌격인 염료감응형 태양전지에 비해 효율이 2배 가까이 높다. 염료감응형 태양전지는 햇빛을 받으면 전기를 발생시키는 염료를 이용한 것으로 현재 최고 효율이 11.9% 수준이다.
석 연구원은 “미국과 중국이 선점하고 있는 실리콘 태양전지의 최고 효율은 25.6% 수준이지만 이 효율을 달성하기까지 60년가량 걸렸다”면서 “페로브스카이트 태양전지는 5년 만에 효율 20%의 장벽을 넘은 만큼 5~10년 안에 상용화될 것”이라고 말했다.
영국 옥스퍼드대가 공동 출자 형태로 설립한 태양전지 기업인 ‘옥스퍼드 포토볼테익스’는 2017년까지 페로브스카이트 태양전지를 제품으로 만들어 출시할 계획을 발표한 바 있다. |
A perovskite solar cell using methylammonium lead bromide and formamidinium lead iodide (far right) sets a new
efficiency record © NPG
South Korean researchers have revealed the chemical secrets that have helped them power the ongoing surge in perovskite solar cell efficiency. Sang Il Seok from the Korea Research Institute of Chemical Technology (KRICT) and his team combined the most widely-used methylammonium lead halide perovskite materials with formamidinium lead iodide. This material helped to make a solar cell that absorbs more solar energy, delivering the record 17.9% efficiency level officially recognised by the US National Renewable Energy Laboratory (NREL) last May.
This is already competitive with commercial silicon solar cells, but in November 2014 NREL confirmed that Seok’s team had gone further still, reaching 20.1% efficiency. Though the chemists are yet to publish full details, Seok tells Chemistry World that the cell uses the same material combination, but with a new fabrication process.
Originally the name of a calcium titanate mineral, perovskite now more commonly refers to the material class that shares its AMX3 crystal structure. Photovoltaic perovskites are hybrid organic–inorganic materials, with methylammonium ions usually in the A position, lead or tin as metal ion M and halogen ions as the X component. Work on perovskites has progressed rapidly since cells with an efficiency of 3.8% were first reported in 2009. That’s because their electronic structure is well suited to light absorption, they conduct the subsequently mobilised electrical charges well and are simple to work with, easily crystallising from solution.
The perovskite usually serves as just one level in a multilayer sandwich stack, with other materials helping the photovoltaic current into the electrical circuit the cell’s connected to. Seok’s team had previously developed an especially efficient sandwich, with an extra layer mixing transparent, electron-transporting mesoporous titania electrodes into their methylammonium perovskite material.
Formidable formamidinium
Other researchers had previously swapped methylammonium for formamidinium ions, which gave perovskites with electronic structures that absorb a greater proportion of the light hitting them. However, when exposed to ambient temperature and moisture the formamidinium perovskites reorganised into an unwanted non-perovskite structure. To avoid this problem, the KRICT team incorporated increasing amounts of methylammonium lead bromide into formamidinium lead iodide cells, exploiting their efficient design. At 15% methylammonium lead bromide, efficiency peaked at around 18% while the perovskite phase also stayed stable.
Martin Green from the University of New South Wales in Sydney, Australia calls this efficiency record ‘a notable step’, but stresses that the design is not ready for widespread use. ‘The cells are tiny, less than 0.1cm2, over 2000 times smaller than a normal commercial silicon cell and, perhaps significantly, there is no discussion of moisture or UV tolerance.’
That concern is potentially significant because perovskites are generally water soluble, and degradation caused by moisture in the air could prevent their widespread use in electricity generation. Seok acknowledges this concern, and says that their stabilised formamidinium-based perovskite is hardier under ambient conditions than exclusively methylammonium-based varieties. The KRICT cell design also reduces the extent of hysteresis, another problem common in perovskites that could cause their efficiency to fall on initial exposure to sunlight. Consequently, while Seok says his team is still seeking further physical insights into perovskites, they are also now working on basic technology for commercialisation.
Annamaria Petrozza from the Italian Institute of Technology in Milan underlines that these latest improvements result from the large-scale perovskite crystal structure. ‘The presence of various types of chemical interactions and structural disorder play an important role,’ she says. ‘This is the beauty and the challenge perovskites have presented so far. Sang II Seok and his team show the importance of controlling the structural–compositional properties and that the panorama of possible strategies to further improve device performance, stability and processability is still very wide.
http://www.rsc.org/chemistryworld/2015/01/new-ion-continues-perovskite-solar-cell-record-flat-out-progress
"from past to future"
데일리건설뉴스 construction news
콘페이퍼 conpaper
.
