Solar photovoltaic power generation is one of the most direct ways to convert solar radiation into electricity. It is a clean form of energy with zero-emission, no effluent, no noise and no vibrations. The coming decades and centuries will likely see massive further growth in this renewable energy consumption. To meet this demand, it requires incremental improvements in existing technologies or the creation of completely new and novel methods.
Our research aim is to increase the power conversion efficiency and operational stability of organic solar cells (OSCs) and perovskite solar cells (PVSCs) with strategies from Chemistry, Materials Science, Physics, and Engineering. We are focusing on materials design/synthesis, device innovation, and upscaling technologies to bring the OSCs and PVSCs to commercilization.
Functional Material Synthesis (Conjugated Materials and Organic/Inorganic Nanomaterials）
Conjugated organic materials play an important role in the development of PVSCs and OSCs. For PVSCs, transporting materials can not only facilitate the extraction and transport of charge carriers at the interfaces, but also help reduce charge recombination and enhance the stability of devices by forming a barrier between ambient environment and the perovskite layer. On the other hand, conjugated materials acts as the active layer in OSCs, especially the development of non-fullerene acceptors (NFAs), enabling rapid growth of photovoltaic performance.To facilitate the commercialization of solar cells, our group pays much attention to the design and synthesis of novel functional materials, such as non-fullerene acceptors, polymer donors & acceptors, charge carrier transporting materials and nanomaterials.
It is said that “Interface is device”. Indeed, interface non-radiative recombination caused by either mis-matched energy level alignment, surface defects and charge- carrier back transfer plays a pivotal role in device performance. In our group, the concentrated research works in recent decades have boosted the power conversion efficiencies (PCEs) of perovskite solar cells to ~24% by the development of interface engineering. More importantly, our developed interfacial materials enable the resultant PVSCs with significantly enhanced operational stability and reduced risk of environmental contamination. As for organic solar cells (OSCs), though delicate photoactive materials design is the main power for the unprecedented progresses in efficiency, the study of interfacial materials is equally important whether for further enhancing their efficiencies or operational stabilities. In this regard, we have developed various self-assembled monolayers (SAMs) to modify either ITO or interface between bulk-heterojunction layer (BHJ) and Ag electrode, which are proved to be very effective for tuning the energy alignment and passivate the defects at the interface.
With the emergence of metal halide perovskite materials (ABX3), which is earth-abundant and extremely ideal light absorber for light-to-electricity conversion, great efforts from both academia and industry have been devoted to perovskite-based photovoltaic devices in the last decade. Our group seeks to develop high-performance PVSCs with inverted configuration (i.e., p-i-n structure) that can be facilely fabricated by a low-temperature solution process, which is widely used for perovskite-based tandem solar cells and highly compatible with various flexible substrates. We have combined the efforts of perovskite composition, additive, and interface engineering to continuously increase the efficiencies of PVCSs with enhanced operation stability and reduced risk of environmental contamination. Meanwhile, we are developing high-efficiency and mechanically robust flexible PVSCs (F-PVSCs) and their integration with various smart sensors, aiming to extend the potential applications of F-PVSCs in the coming Internet of Things (IoTs) aera.
OSCs represent a transformative technology with great potential for extremely high-throughput manufacturing at very low cost and are made from non-toxic, earth-abundant materials with low energy inputs. They have the potential to serve lightweight, flexible, conformal, and low-cost solid-state power sources. However, their performance must be improved before they can be viable for commercial applications.
Currently, our group achieved a single-junction OSC with officially certified record efficiency of 17.5% and 17.7%. This achievement is noted as a major technological breakthrough in the renowned NREL chart of “Best Research-Cell Efficiencies”. Nevertheless, there is still an obvious gap between the record performance of OSCs and other thin-film photovoltaic technologies such as perovskites and gallium arsenide (GaAs). Therefore, continuous improvements in material design and device fabrication are urgently needed.
Tandem or multi-junction solar cells utilize two or more sub-cells made of photovoltaic absorbers with different bandgaps so that the sun’s spectrum can be used much more efficiently. The world-record device efficiency of single-junction solar cells based on organic-inorganic hybrid perovskites has reached 25.5%. Further improvement in device power conversion efficiency (PCE) can be achieved by either optimizing perovskite films or designing novel device structures such as perovskite-based tandem solar cells. We are developing both low-bandgap and wide-bandgap perovskites for all-perovskite tandems; low-bandgap organic materials for perovskite/OPV tandems; and wide-bandgap perovskite for perovskite/Si tandems. In addition, to tackle the challenges of the interconnection layer for tandem solar cells, we are developing high-performance interlayers using state-of-the-art thin-film deposition techniques such as atomic layer deposition and sputtering.
Multi-junction Solar Cells
Large-Sized Solar Modules
Currently, both the organic and perovskite PV technologies are still in the laboratory research stage. Although the world-record power conversion efficiency (PCE) of PVSCs has reached 25.7%, its device area is less than 0.1 cm2, limiting its real outdoor applications. In addition, PVSCs possess unique advantages over other PV technologies in terms of scalability, flexibility in applications, and low-cost for precursor materials and manufacturing. However, such unprecedented PV technology also shows some intractable shortcomings that need to be overcome before commercialization, especially the big lab-to-fab gap in device performance.
We are focusing on the fabrication of perovskite mini-modules with the size of 5 cm × 5 cm using blade-coating and slot-die coating methods by transferring our small-size device fabrication experience including materials composition engineering, interface engineering, and defects passivation engineering. We also explore engineerings for upscaling the OSCs