Solar Cells

Above - Schematic illustration for the application of a tape stripping method. The adhesive tape is a regular transparent Scotch tape (model #: S-9782). 

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Solar Cells

CO2 doping of organic interlayers for perovskite solar cells 


Doped organic semiconductors are often used as charge-extraction interlayers in perovskite solar cells and Spiro-OMeTAD is the most frequently used semiconductor in the hole-conducting layer. Its electrical properties affect the charge collection efficiencies of the solar cell. So, to enhance the electrical conductivity of spiro-OMeTAD, LiTFSI, a metal salt, is typically used in a doping process, initiated by exposing the spiro-OMeTAD:LiTFSI blend films to air and light for several hours. This process, in which oxygen acts as the p-type dopant, is time-intensive and hinders the commercialization of solution-processed perovskite solar cells. To tackle this issue, the TMD lab has developed a fast and reproducible doping method that involves bubbling a spiro-OMeTAD:LiTFSI solution with CO2 under ultraviolet light promoting its p-type doping. CO2-treated interlayer exhibits 3 times higher conductivity than a film doped with conventional techniques while realizing stable, high-efficiency perovskite solar cells without any post-treatments. This method can also be used to dope π-conjugated polymers, such as P3HT. This work is published in Nature

Efficiency limits of underwater solar cells


Most attempts to use solar cells to power underwater systems have had limited success due to the use of silicon, which has a relatively narrow band gap and absorbs ultraviolet (UV), visible, and infrared (IR) light. Because of absorption by water, most of the IR light from the sun is absorbed at relatively shallow depths, and wider band-gap semiconductors, which primarily absorb visible light, should therefore be used. To understand how efficient underwater solar cells can be and what band gaps are optimum in deep waters, we combined oceanographic data with detailed balance calculations to show that solar cells can harvest useful power at water depths down to 50 m with very high efficiencies. Our findings show that underwater solar cells can efficiently generate useful power in very deep waters but should employ much wider band-gap semiconductors than what are currently used today.

FRET Based Organic Solar Cell

There are two crucial tasks for realizing high-efficiency polymer solar cells (PSCs): 

1. Increasing the range of the spectral absorption of light

2. Efficiently harvesting photogenerated excitons

Nature is always our best teacher. Considering how small the photosynthetic reaction sites are in a leaf, some highly efficient ways of transferring, e.g. Förster resonance energy transfer (FRET), the captured photon energy from the pigments to reaction centres must come into play. Although FRET is a well-studied phenomenon in other areas of research, there had been very little effort to employ FRET to improve solar cell performance. To realize this idea, we specifically selected a photoactivematerial with a high light absorption coefficient and a  counterpart to comply the absorption-emission spectrum overlapping rule of FRET.

FRET-based polymer cells address several problems: The limited spectral absorption, control of nanomorphology, and inefficient harvesting of photo-generated excitons.

1. The P3HT mainly absorbs green and orange light, while squaraine dye highly absorbs red and near-infrared light in a complementary manner. Introducing squaraine thus increases the spectral range of light absorption.

2. The squaraine prefers to dwell at the interfaces of P3HT and PCBM, leading to developed ordering of the interpenetrating network.

3. The properties of the P3HT and squaraine optically satisfy conditions for non-radiative energy transfer process, i.e. FRET, which facilitates the smooth migration of excitons towards the interfacial heterojunctions where charge separation occurs.

This architecture transcends traditional multiblend systems, allowing multiple donor materials with separate spectral responses to work synergistically, thereby enabling an improvement in light absorption and conversion. Our approach offers a more viable solution than designing or seeking a single material to capture energy from the full solar spectrum. By strategically combining different materials with the proper spectral range to take advantage of FRET, more photo-excited energy, which may dissipate as heat, can be extracted out of solar cell into electricity. This opens up a new avenue for the development of high-efficiency polymer solar cells

Related Publications:

CO2 doping of organic interlayers for perovskite solar cells Jaemin Kong, Yongwoo Shin, Jason A Röhr, Hang Wang, Juan Meng, Yueshen Wu, Adlai Katzenberg, Geunjin Kim, Dong Young Kim, Edward Chau, Francisco Antonio, Tana Siboonruang, Sooncheol Kwon, Kwanghee Lee, Jin Ryoun Kim, Miguel A Modestino, Hailiang Wang, and André D.Taylor. Nature 2021, 594, 51

Efficiency Limits of Underwater Solar Cells, Jason A. Röhr, Jason Lipton, Jaemin Kong, Stephen A.Maclean, and André D. Taylor. Joule 2020, 4, 840

Underwater Organic Solar Cells via Selective Removal of Electron Acceptors near the Top Electrode, J. Kong, D. Nordlund, J. S. Jin, S. Y. Kim, S.-M. Jin, D. Huang, Y. Zheng, C. Karpovich, G. Sertic, H. Wang, J. Li, G. Weng, F. Antonio, M. Mariano, S. Maclean, T.-H. Goh, J. Y. Kim, and A. D. Taylor. ACS Energy Letters, 2019, 4 1034. 

Co-evaporated Bi-squaraine Inverted Solar Cells: Enhancement Due to Energy Transfer and Open Circuit Voltage Control, Tenghooi Goh , Jing-Shun Huang, Elizabeth A Bielinski , Bennett A. Thompson , Stephanie Tomasulo , Minjoo L. Lee , Matthew Y. Sfeir , Nilay Hazari , and Andre D. Taylor. ACS Photonics, 2015, 2, 86

The Role of HF in Oxygen Removal from Carbon Nanotubes: Implications for High Performance Carbon Electronics, Xiaokai Li, Jing-Shun Huang, Siamak Nejati, Lyndsey McMillon, Su Huang, Chinedum Osuji, Nilay Hazari, André D. Taylor, Nano Letter 2014, 14, 3388

Controlled doping of carbon nanotubes with metallocenes for application in hybrid carbon nanotube/Si solar cells. Xiaokai Li, Louise M Guard, Jie Jiang, Kelsey Sakimoto, Jing-Shun Huang, Jianguo Wu, Jinyang Li, Lianqing Yu, Ravi Pokhrel, Gary W. Brudvig, Sohrab Ismail-Beigi, Nilay Hazari and André Taylor, 2014, Nano Letters, 14 (6), 3388–3394.

Device Area Scale-Up and Improvement of SWNT/Si Solar Cells Using Silver Nanowires. Xiaokai Li, Yeonwoong Jung, Jing-Shun Huang, Tenghooi Goh and André D. Taylor, 2014, Advanced Energy Materials, 4, 1400186.

Polymer bulk heterojunction solar cells employing Forster resonance energy transfer. Jing-Shun Huang, Tenghooi Goh, Xiaokai Li, Matthew Y. Sfeir, Elizabeth A. Bielinski, Stephanie Tomasulo, Minjoo L. Lee, Nilay Hazari and André D. Taylor, 2013, Nature Photonics, 7, 479-485.

Improved Efficiency of Smooth and Aligned Single Walled Carbon Nanotube/Silicon Hybrid Solar Cells. Xiaokai Li, Yeonwoong Jung, Kelsey Sakimoto, Teng-Hooi Goh, Mark Reed and André Taylor, 2013, Energy & Environmental Science, 6 (3), 879 – 887.

Record High Efficiency Single-Walled Carbon Nanotube/Silicon p–n Junction Solar Cells. Yeonwoong Jung*, Xiaokai Li*, Nitin K. Rajan , André D. Taylor, and Mark A. Reed, 2013, Nano Letters, 13, 95-99. (*Jung, Y. and *Li, X equally contributed to this work).