Investigation On Key Materials And Device Structures For Highly Efficient And Stable Perovskite Solar Cells

Organic-inorganic halide perovskites,denoted as ABX₃ [A = Cs+,CH₃NH₃⁺（MA⁺）,or NH=CHNH₃⁺（FA+）;B = Pb or Sn;X = Br,I or Cl],have recently attracted researchers’ great interest owning to their outstanding advantages as light absorbers for photovoltaic applications,such as direct and appropriate band gap,large absorption coefficient,high carrier mobility as well as ambipolar charge transport.Organic-inorganic halide perovskite solar cell（PSC）encourages even more efforts of the research community from both academia and industry to expedite the commercialization process because of its high efficiency,low-cost,low temperature process,transparency and mutiple color.Although the certified power conversion efficiency（PCE）for PSC have yeiled to 22.1%,the major challenge for bringing this technology for commercialization lies in its long-term environmental stability.In this thesis,we firstly explored p type perovskite sensitized solar cell.To improve efficiency and stability of PSC,four main approaches has been used:（1）In this work,we demonstrated effective photocathodes based on novel organometal halide perovskites sensitized mesoporous NiO in liquid electrolyte based p-type solar cells.A decent Voc and Jsc up to 205 mV and 9.47 mA cm^-2 have been achieved based on the MAPb I₃/NiO solar cell at 100 mW cm^-2 light intensity,which is significantly higher than any of previously reported liquid electrolyte based p-type solar cells based on sensitizers of organic dyes or inorganic quantum dots.The dense blocking layer made by spray pyrolysis of nickel acetylacetonate holds the key on determining the current flow direction of the solar cells.The good research basis allows us to firstly design a novel pn tandem solar cell by combination of organic dye（N719）sensitized n-type TiO₂ photoanode and organometal halide（MAPb I₃-xClx）sensitized p-type NiO photocathode,by sharing the same iodine liquid electrolyte.The Voc of our tandem cell reached 1050 mV with efficiency up to 4.31% which is also superior to most of previously reported pn dye sensitized tandem solar cells with efficiency of 1.91%.（2）However a rapid degradation of performance was witnessed due to dissolution of the perovskite in the I₃-/I-electrolyte.Considering the structure of solid-state dye sensitized and organic solar cells,many researchers developed a new solid-state solar cells（FTO glass/c-NiO/perovskite/PCBM/Bis-C60/Ag）employing FA1-xMAxPb（I1-yBry）3 perovskite as a light absorber.FA1-xMAxPb（I1-yBry）3 compositional perovskite recently was frequently reported in high efficiency PSCs,benefiting from their high quality crystal,tunable bandgaps,wide absorption spectrum and stability.In this work,a two-step method by inter-diffusion of spin-coated stacking layers of PbI2 and FAI_0.85MABr_0.15 has been implemented to fabricate high quality FA0.85MA0.15Pb（I0.85Br0.15）3 films.By optimizing the concentrations of FAI_0.85MABr_0.15 to 40 mg mL-1,high quality FA0.85MA0.15Pb（I0.85Br0.15）3 films are formed with pure perovskite phase,larege scale crystal and long lifetime.Applied this compositional perovskite into inverted FTO glass/c-NiO/ PCBM/perovskite/Bis-C60/Ag,Voc,Jsc and FF have reached 1101 mV,21.45 mA cm-2 and 0.76 with high efficiency with 17.95%.We also found unreacted Pb I2 and δ-FAPb I₃ had effect on the stability of PSC.（3）For the regular n-i-p configuration PSC,the hole-transporting layer（HTL）used so far is mainly based on p-type organic semiconductors such as Spiro-OMeTAD,which is relative high cost,low conductivity and tend to interact with water.CuGaO₂ shows low-temperature solution process,higher mobility and stability,which is very promising hole transport layer candidate for improving photovoltaic performance,device stability,and fabrication cost of PSC.By applying CuGaO₂ into FTO glass/c-TiO₂/perovskite/CuGaO₂/Au structure,high efficiency with 18.51% has reached.Moreover,the CuGaO₂ layer with high hole mobility and environmental stability helps isolate the perovskite and Au layers to significantly enhance device’s photovoltaic performance and long-term stability（with > 80% of its initial PCE remained after 30-days storage in air at room temperature）.（4）Full printable processed mesoscopic perovskite solar cell with carbon as cathode has draw wide concern for its’ long-term stability.In this work,a new compositional perovskite MAPbI₃（SrCl₂）_x thereafter has been introduced into this architecture.We chemically modify the MAPbI₃ perovskite by substituting PbI₂ with SrCl₂ in the precursor solution.Structural,elemental,and morphological analyses show that the incorporation of SrCl₂ affords the formation of MAPbI₃（SrCl₂）_x perovskites endowed with lower defect concentration and better pore filling in the derived mesoscopic PSCs.By employing MAPb I₃（SrCl₂）_0.1 into FTO glass/c-TiO₂/m-TiO₂/m-Al₂O₃/m-Carbon structure showed PCE of 15.90%.Besides enhanced PCE,the MAPbI₃（SrCl₂）_0.1 based PSC also affords an improved stability.Exposing unencapsulated MAPb I₃（SrCl₂）_0.1 based PSC to 10 mW cm^-2 light intensity using white LED for 1000 h,the PCE remained 90% of the initial value.