Promotion Of Carrier Transport And Stability In N-i-p Perovskite Solar Cells

Solar energy is a kind of green and renewable energy sources,considered as a potential alternative for fossil energy.The working mechanisms for solar cells are based on photovoltaic effect,including four processes,i.e.,light absorption,carrier separation,carrier transport and charge collection.Among many kinds of solar cells,perovskite solar cells(PSCs)stand out as the most promising new-generation solar cells,benefiting from the high energy conversion efficiency(PCE),low-cost,scalable fabrication,flexibility etc.In the present research,PSCs with n-i-p configuration(regular cells)are studied extensively due to their superior photovoltaic performance compared with p-i-n devices.Power conversion efficiency(PCE)and stability are two main factors for commercial application of PSCs.In order to promote PCE and stability for n-i-p PSCs,we made efforts to control the transition method of bulk perovskite materials and modify the two interfaces beside hole transport layers,promoting carrier transport efficiency in PSCs.Consequently,small-area solar cells and large-area solar modules have been fabricated with both high efficiency and excellent stability.The main research contents and results are as follows:Chapter 1.Starting from the working principles,material properties and developing history of PSCs,we highlighted the significance of improving carrier transport and stability of n-i-p devices,followed by introduction of the main issues and current solutions.Then,based on the research background,we proposed the design philosophy and research content of each chapter.Chapter 2.Based on the characterization of crystal structure and film structure,we figured out the one-dimensional structure of perovskite intermediate.From the aspect of intermediate structure,we find out the reason for different quality of bulk perovskite film deposited from precursors with varied amount of DMSO or NMP additive.As compared with DMSO,NMP has a larger addition window in perovskite film deposition,showing advantages in large-scale perovskite film fabrication.Chapter 3.We developed a new bulk perovskite conversion method,that is,vapor-assisted conversion from two-dimensional perovskite to three-dimensional perovskite.This new conversion route obtains pure α-FAPbI3 at a relatively low annealing temperature,benefiting from the low transition energy.The lowtemperature annealed perovskite film has low trap-state density and high carriertransfer efficiency.As compared with traditional phase conversion method from δFAPbI3 to α-FAPbI3,this new conversion route endows PSCs with higher PCE(15.96%vs.19.32%)and better stability.Chapter 4.We introduced an interfacial modification strategy by inserting perovskite quantum dots(QDs)into the interface between perovskite and dopant-free organic hole transport layer(HTL).The multiple functions of QDs were demonstrated:1)passivating the trap states on perovskite layer;2)building cascade energy levels between perovskite and HTL;3)enhancing the structural regulation and crystallinity of organic HTLs.Consequently,the efficiency for carrier transport within PSCs can be increased largely with QD interfacial modification,promoting PCEs and stabilities of PSCs with various dopant-free organic HTLs.Chapter 5.We intercalated perovskite QDs into the interface between perovskite and inorganic nanoparticle HTL and demonstrated that QD interlayer can enhance the self-assembly behavior of inorganic narioparticles,thus improving the film compactness and nanoparticle regulation of HTL.With QD modification,the hole transport efficiencies in the inorganic-HTL-based devices are greatly improved.Based on the high stability of inorganic materials,the corresponding PSCs with QD interfacial modification show excellent long-term stability(sustaining over 86%of initial PCE)after 1000-hour aging test under extreme condition(85℃,85%relative humidity).Chapter 6.We developed an interfacial modification strategy to promote PSCs with Cu positive electrode.We modified the inner surface of Cu(i.e.,the interface between HTL and electrode)using mercaptopyridine-based molecules with various substitutes.We demonstrated that the increase of work function and oxidation potential can enhance the hole transfer efficiency at the interface and promote the anti-corrosion capability of Cu electrode.The molecular interfacial modification of Cu endows Cu-electrode n-i-p devices with high PCE(22.90%),excellent storage stability under extreme condition and good working stability during continuous output.Chapter 7.Finally,conclusions on design philosophy and results have been given.What is more,we proposed prospects from the aspects of improving PCE,enlarging fabrication,promoting stability,and ensuring eco-friendly production,in order to pose the challenges in commercialization of PSCs.