Investigation Of Working Principles, Charge-selecting Materials And Stability For Perovskite Solar Cells

Organic-inorganic hybrid perovskite, with the organic component filling the coordinated space between the inorganic octahedrals, is a class of self-assembled crystal material. Taking advantages of organic and inorganic parts, it has excellent performance in optical, electrical, and magnetic field. Recently, the research and application of typical organic-inorganic hybrid perovskite (CH3NH3PbI3) in photovoltaic have attracted much attention, due to high absorption coefficient and ambipolar charge transport properties as well as flat, highly uniform thin films of CH3NH3PbI3.ro date, the solar cell power conversion efficiencies have achieved?21%. This value is very greater than those of conventional dye-sensitized or organic solar cells.In this work, we firstly explored high performance mesoscopic perovskite solar cells with different hole transport material and counter electrode, involving FTO/c-Ti02/m-Ti02(CH3NH3PbI3)/CH3NH3PbI3/spiro-MeOTAD/Auand FTO/c-TiO2/m-TiO2(CH3NH3PbI3)/m-Al2O3(CH3NH3PbI3)/m-NiO(CH3NH3PbI3)/Carbon configurations. Then, temperature dependent photovoltaic parameters of both devices have been carefully investigated to illustrate the determination of Voc and charge recombination by using temperature and light-intensity dependent photocurrent-voltage characterization. Our results show that the temperature dependence of Voc for perovskite solar cells deviate from that having a linear linear behaviour observed as a rule for organic and inorganic solar cells. This results from the great role of CH3NH3PbI3 in the construction of built-in electric field, accompanying with the charge transportion and accumulation in perovskite. Accurately, it should be correlated to the permittivity of CH3NH3PbI3 for their similar temperature and light-intensity dependent behaviour. Temperature-dependent impedance spectroscopy helps to reveal these physical processes, and emphasizes the advantage of inorganic hole transport material in mesoscopic perovskite solar cells. Furthermore, the hysteresis effect is ascribed to ion motion in perovskite.Based on the understanding of working principles for perovskite solar cells, we report an investigation on the alternative hole/electron transport layers to replace typical spiro-OMeTAD, TiO2 and PCBM. A promising hole transporting material using a spirothiophene derivative with 4,4'-spirobi[cyclopenta[2,1-b;3,4-b']dithiophene] as the spiro core for perovskite solar cells, exhibiting an overall power conversion efficiency of 10.4%. A conjugated backbone composed of fluorene, naphthalene diimide and thiophene spacers (PFN-2TNDI) was introduced as an alternative electron transport layer to replace the commonly used PCBM in the inverted p-i-n planar-heteroj unction perovskite solar cells and achieved a power conversion efficiency of 16.7%. A small molecule semiconductor amino-substituted perylene diimide derivative (N-PDI) has been explored as an alternative electron transport layer to replace the common TiO2 in the regular planar heteroj unction perovskite solar cells and obtained a power conversion efficiency of 16.2%. The characterizations of photoluminescence (PL), time-resolved PL decay and impedance spectroscopy reveal the new electron transport layers with amino group as the terminal substituent not only possess high electron molibility, but also effectively passivate the surface traps of perovskite to improve the performance of pervoskite devices.In order to improve the stability, we propose interfacial modification between perovskite and charge transport layer to not only block perovskite degradation from polar solvent and additives, but also effectively improve the charge lifetime. This results in the enhancement of both the stability and the performance of pervoskite devices.