Device Physics And Engineering Of Perovskites And Polymer Solar Cells

The new generation of photovoltaic technologies,such as hybrid organometal trihalide perovskite solar cells and polymer bulk heterojunction solar cells(PSCs),has emerged as an attractive technology for renewable energy generation,with the potential advantages of low-cost manufacturing on lightweight flexible substrates by solution fabrication methods.In addition to the development of novel active layer materials,interface engineering has played an important role on the rapidly improved performance of photoelectric devices.The research demonstrated in this thesis focuses on the device physics and engineering of two rapidly developed optoelectronic devices:perovskites and polymer solar cells,especially on the aspects that are important for the commercialization of the photovoltaic technologies,such as low cost,high eff-iciency,large area printing process,and semitransparent cell application.In chapter II,organic halide salts were introduced as a processing additive to modulate the morphology and crystallinity of perovskite light-absorbing layer in organic-inorganic hybrid planar heterojunction solar cells.Among different organic halide processing additives tested in this study,tetraphenylphosphonium iodide(TPPI)and chloride(TPPCl)were found to be the most efficient ones in improving the crystallinity and coverage of the CH3NH3PbI3-xClx perovskite films and TPPI was also explored as an interfacial n-dopant which reduced the contact resistance at the cathode interface.As a result,planar-heterojunction perovskite solar cells employed these dual-functional phosphonium halides showed enhanced performance with power conversion efficiency(PCE)of 13%,while unmodified cells only showed PCE of?10%.In chapter ?,an amino-functionalized copolymer with a conjugated backbone composed of fluorene,naphthalene diimide and thiophene spacers(PFN-2TNDI)was introduced as an alternative electron transport layer(ETL)to replace the commonly used[6,6]-phenyl-C61-butyric acid methyl ester(PCBM)in the p-i-n planar-heterojunction organometal trihalide perovskite solar cells.We found that the amines on the polymer side chains not only can passivate the surface traps of perovskite to improve the electron extraction properties,they also reduce the work function of the metal cathode by forming desired interfacial dipoles.With these dual functionalities,the resulted solar cells outperformed those based on PCBM with PCE increased from 12.9%to 16.7%based on PFN-2TNDI.In addition to the performance enhancement,it is also found that a wide range of thicknesses of the new ETL can be applied to produce high PCE devices owing to the good electron transport property of the polymer,which offers a better processing window for potential fabrication of perovskite solar cells using large-area coating method.In chapter IV,we report a new and universal strategy for the interface engineering of non-fullerene polymer solar cells by using an n-type water/alcohol soluble conjugated polymer(PFN-2TNDI)as a cathode interlayer,which results in the state-of-the-art non-fullerene PSCs with a maximal PCE of over 11%.It was found that PFN-2TNDI works as both the charge collection interlayer and the light harvesting layer,which can enhance electron collection and contribute to photocurrent production in the resulting devices.Our results therefore not only provide a universal approach for the interface engineering of non-fullerene PSCs,but may also open up new design directions for ternary device architectures with a third component in the interface.This open a new avenue for the future design of multifunctional interlayers for further enhancement of high performance PSCs.In chapter V,we report non-fullerene semitransparent solar cells that exhibit over 7.5%efficiency with a high visible light transmission of-25%.The photon-to-charge conversion up to almost 85%that of its opaque counterpart.In addition,these semitranspatent solar cells can also serve as heat-insulating films for smart windows due to the use of non-fullerene acceptor with an enhanced absorption in the near-infrared.