Passivation of Perovskite with Fluorinated Polymer
In this work, we applied dithienobenzodithiophene-based π-conjugated polymer consisting of fluorinated benzotriazole and benzothiadiazole through anti-solvent method to passivate the defects of perovskite crystals. The fluorinated polymer interacts with under coordinated Pb2+ ions in the perovskite crystals to form Pb-F bond which effectively passivates the defects. As a result, a power conversion efficiency (PCE) of 18.03% is achieved in the champion cell. Moreover, the defect passivation blocks the pathway for moisture to diffuse into perovskite film, preventing the decomposition of the perovksite crystal. Therefore, the device retains 90% of the original PCE even after storing in an ambient environment with 60% relative humidity for 1000 h. The related work was published in Solar RRL, DOI: 10.1002/solr.201900029 and highlighted at MaterialsViewsChina (https://www.materialsviewschina.com/2019/03/35455/)
Saddle-shaped Small Molecule as Bi-functional Hole Transporting Layer (HTL)
In the collaboration work with Prof Li Gongqiang from Nanjin Tech University, we design and synthesize a saddle-shaped organic small molecule named α, β-COTh-Ph-OMeTAD. This bi-functional small molecule serves as a dopant-free HTL as well an interfacial layer to passivate the perovskite. With the dopant-free α, β-COTh-Ph-OMeTAD as a HTM and an interfacial layer, the perovskite solar cells (PSCs) exhibits a power conversion efficiency PCE of 17.22%, which is higher than that of device based-on conventional, doped spiro-OMeTAD (16.83%). Our work opens a new avenue for efficient and stable PSCs by exploring new dopant-free materials as alternatives to spiro-OMeTAD. The related work was published in Solar RRL, DOI:10.1002/solr.201900011
E-skin Project by Undergraduate Students
Perovskite Solar Cell is the fastest growing photovoltaic technology. It made its debut in 2009 with the efficiency of only 3.8% but today the efficiency reaches more than 23%. Despite this rapid progress, long term stability of the device, which originates from the pervoskite crystals as well as dopant in the hole transporting layer, hinders the commercialization of this technology. Dopant-free hole transporting materials (HTM) play a vital role in improving the device stability by eliminating the dopant salt and providing barrier from penetration of moisture into perovskite. Moreover, HTM also serves as interfacial layer to passivate the defects in perovskite. Aiming to improve the stability of the devices, concurrently efficiency, our research focuses on the development of dopant-free hole transporting materials and passivation techniques of pervoskite crystals.
Organic Solar Cell (OSC) is another attractive photovoltaic technology thanks to its low-cost, light-weight and flexible features. The efficiency of the OSC hits a bottleneck at ~ 10%; one of the reasons is fullerene-based acceptor materials which lodge in the active layer of the cell but do not contribute to absorption of visible light. Non-fullerene based acceptors could overcome is bottleneck by providing tunable absorption spectrum to complement with absorption of donors. We are working on the processing techniques for non-fullerene acceptor-based OSC to control the morphology of bulk-heterojunction, to up-scale the device through various printing methods and to eliminate the toxic solvents used in the device fabrication for the green processing.
Flexible/Stretchable Devices for Wearable Electronics: With the development of IoT, the demand for wearable electronics is increasing. They have huge potential in portable health monitoring device, prosthetic hand, fitness monitoring equipment and smart textile. Our research focuses on the fabrication of flexible/stretchable sensors based on organic thin film transistor and other flexible/stretchable materials for e-skin and wearable electronic devices.