Preparation And Photovoltaic Performance Of TiO₂-based Dye-sensitized And Perovskite Solar Cells

So far,solar energy is the most ideal renewable clean energy,which will not produce any pollution.Photovoltaic devices are one of the most effective means to transform solar power to useful electrical power.As new thin-film solar cells,both dye-sensitized solar cell(DSSC)and perovskite solar cell(PSC)posess some advantages such as simple preparation procedure,low cost and high photoelectric conversion efficiency,with absolutely great development potentials,which have been concerned and studied more and more widely.In the DSSCs,photoanode still has some problems such as insufficient incident-light use ratio and lower adsorbing capacity of photoanode semiconductor film dye as the most important component currently,due to the wide band gap of TiO2.All these problems directly affect the photoelectric conversion efficiency of DSSC.Therefore,the optimization and modification of structure and performance of photoanode films are becoming one of these important research directions to improve device's photoelectric conversion efficiency by adjusting the semiconductor's wide band gap,broadening its visible-wavelength response range,improving the adsorbing ability of film dye and reducing the electron recombination within the film.In perovskite solar cells,the stability of perovskite films directly affects the application of the devices while lead in the films will cause the possible pollution problems for the later recovery.Therefore,the development of lead-free perovskite has become the focus of the study of perovskite solar cells,which are associated with the sudy of improving the preparation process and enhancing the stability of perovskite films.In this study,aiming at the above problems with DSSCs and PSCs,the TiO2 composites and photoanode films with different structures would firstly be prepared,which would be applied in the liquid-state and solid-state dye-sensitized solar cells,respectively and then the influence of different composite nanomaterials and photoanode structures on cell's photovoltaic performance as well as possibility mechanisms would be investigated and discussed.Secondly,the stability of perovskite films would be improved via a novel annealing process.Finally,a new perovskite solar cell material would be prepared by using Bi as central kation to replace Pb and then the material performance and the device's photovoltaic performance would be evaluated.The specific research contents are as follows:(1)In this work,a novel multistage structure dye-sensitized solar cell(DSSC),which consists of Ag nanowires(AgNWs),TiO2 nanoparticles and graphene wrapped TiO2 mesoporous microspheres(GTMs),was fabricated by using simple spin coating steps.The aim of this study was to modify the bandgap of GTMs by using graphene so as to promote the light absorption of GTMs in the visible light region and in turn to improve the power conversion efficiency(PCE)of DSSCs.Additionally,graphene and AgNWs can enhance the electron transfer in the DSSC to further improve the PCE of DSSCs.The effect of AgNWs and GTMs light scatting layer on the photovoltaic performance of DSSCs was investigated.The results showed that a PCE of 6.93%was achieved for the DSSC co-modified by GTMs and AgNWs,which was about twice as much as that for the DSSCs only with a TiO2 nanoparticle layer(with a PCE of 3.53%).This present study might open a new avenue for the improvement of the PCE of DSSCs.(2)In this study,g-C3N4 with higher preparation technology yet lower cost was taken to replace graphene and recombine with TiO2,the g-C3N4/TiO2 composite microspheres were prepared respectively and applied into the photoanode of liquid-state dye-sensitized cell.The photoelectric conversion efficiency of the device prepared achieved Jsc= 15.52 mA/cm2,Voc= 0.725 V,FF= 0.648,PCE= 7.29%,which was increased by 55%compared to the control cell.In addition,solid-state dye-sensitized solar cells(ss-DSSCs)were fabricated with g-C3N4 and Ag co-modified TiO2 nanoparticles as photoanode materials.Devices with spiro-OMeTAD as hole transport materials(HTMs)showed a high power conversion efficiency(PCEs)of 6.22%.For the heterostructured g-C3N4/Ag/TiO2 nanocomposites,Ag nanoparticles were deposited as an electron-conduction bridge between the TiO2 surface and the g-C3N4 layer to increase absorption in the visible-light region via surface plasmon resonance,whilst the interface between Ag/TiO2 and g-C3N4 stimulated the direct migration of photo-induced electrons from g-C3N4 to Ag/TiO2,which was conducive to suppressing the recombination of electron-hole pairs.These results show that the performance of ss-DSSCs was significantly enhanced after modification with g-C3N4 and Ag,suggesting that heterostructured g-C3N4/Ag/TiO2 composites can provide high photoelectric conversion through an effective electron transfer process.It had a great significance to the cell cost reduction and performance improvement of solid-state dye-sensitized cell.(3)So far,the stability of perovskite solar cell is still an obvious disadvantage.In order to improve the stability,the annealing at iodine atmosphere for perovskite films was conducted in the present work.The optimum process conditions were determined by investigating the effect of different iodine atmospheres on the morphology and properties of the perovskite films.The experimental results showed that the annealing at iodine atmosphere significantly enhanced the stability of perovskite films.No obvious decomposition was detected for perovskite films after exposing in the air for 10 days.Under a treatment atmosphere with 100mg iodine,the annealed perovskite film exhibited higher crystallinity and coverage as well as better optical absorption property compared with other treatment conditions and its photoelectric conversion efficiency could reach 13.18%.(4)Aiming at the possible environmental pollution problems caused by the toxicity of lead from lead-containing perovskite,we used BiI3 and formamidine iodine(HC(NH2)2I,FAI)as precursors to synthesize lead-free FA3Bi2I9 perovskite and characterized morphologies and properties of the perovskite films obtained under different processing conditions.The results showed that the obtained FA3Bi2I99 perovskite had good film-forming properties and high stability,and the photoelectric conversion efficiency of the devices using FA3Bi2I9 as light-absorbing layer could reach 0.198%.Up to date,there is little research on bi-based perovskite.This work will have some reference value for further developing and improving the performance of lead-free perovskite solar cells.