Preparation Of Sb₂S₃-based Inorganic Heterojunctions For Solar Cells

Crystalline Sb₂S₃ has been regarded as a promising absorber candidate for solar cells due to its low band gap?1.50-1.70 eV?,high absorption coefficient(?105 cm^-1)and high charge carrier mobilities(?_e = 10 cm²V^-1s^-1 and ?_h=2.75 cm²V^-1s^-1).-This dissertation mainly focuses on exploring the solution-processing methods for the controllable preparation of the heterojunctions based on Sb₂S₃ and metal oxides?ZnO and TiO₂?,studying the correlations between the structure and photon-to-current coversion property of heterojunctions and revealing the photovoltaic principles and the characteristics of charge transport in the related solar cells.The main contents and results are summarized as follows:1.TiO₂/Sb₂S₃ planar heterojunction films are prepared by using chemical-bath-deposition?CBD?method to deposit amorphous Sb₂S₃ nanoparticles onto condensed TiO₂ film and a followed thermall annealing in different atmosphere uner ordinary pressure,and FTO/TiO₂/Sb₂S₃/PCPDTBT/MoO₃/Au planar heterojunction solar cells with a conjugated polymer PCPDTBT film as hole transporting layer and a MoO₃ interfacial layer to adjust the work-function of Au electrode are fabricated.The effects of annealing atmospheres on the composition,structure and photovoltaic properties of the resulting Sb₂S₃ films are investigated.The results demonstrate that Sb₂O₃ secondary phase is produced during the chemical reactions in CBD process and its content gets increased during the annealing under N₂ atmosphere,leading to the Sb₂S₃ of a low purity;however,the thermal annealing in N₂-S atmosphere results in the pure,smooth and highly condensed Sb₂S₃ film,due to the conversion of Sb₂O₃ into Sb₂S₃ by the reaction between Sb₂O₃ and S.It is found that the photogenerated holes evidently contribute to photocurrent generation in the resulting planar solar cells and the elimination of Sb₂O₃ phase leads to the greatly decreased defects for charge recombination and thereby facilitating the carriers transfer of both electron and holes in the bulk Sb₂S₃ layer and the significanltly enhanced charge collection efficiency and photocurrent for improved device performance,eventually resulting in the increased efficiency by 1.34 fold up to 2.04%.2.Using a molecular precursor solution method in combination with a short-time thermal annealing process,we prepare the condensely grown Sb₂S₃ blocks inside TiO₂ nanorod array?TiO₂-NA?of a length of 600 nm,where each block encapsulates several TiO₂ nanorods,resulting in TiO₂-NA/Sb₂S₃ binary bulk heterojunction films.With a conjugated polymer MEH-PPV film as hole transporting layer,FTO/TiO₂-NA/Sb₂S₃/MEH-PPV/MoO₃/Au bulk heterojunction solar cells are fabricated and the effects of the deposited Sb₂S₃ content on device performance are investigated.It is found that the thickness of Sb₂S₃ imposes a significant effect on the performance and the kinetics of charge transportation in those bulk solar cells.As the thickness of St₂S₃ blocks is smaller than the TiO₂-NA length,the carrier transport in the device is mainly controlled by the excitons photogenerated in MEH-PPV,As the thickness of Sb₂S₃ blocks is comparable to the TiO₂-NA length,the devices display the best performance with an efficiency of 0.69%,in which the carrier transport is mainly controlled by the free charge carriers photogenerated in Sb₂S₃ blocks and the photogenerated hole contribution to photocurrent generation is not ignorable.However,the presence of Sb₂S₃ blocks thicker than TiO₂-NA deteriorate the device performance by increasing the resistance and charge recombination inside the devices.3.Using CBD method to deposit amorphous Sb₂S₃ nanopartilces into ZnO-CdS core/shell-structured binary nanorod array?ZC-NA?,in combination with a certain thermal annealing in N2 atmosphere under ordinary pressure,we prepare the ZC-NA/Sb₂S₃ ternary bulk heterojunction film featuring a condensed Sb₂S₃ nanoparticle layer interdigitated with ZC-NA.With a PCPDTBT film as buffer layer and PEDOT:PSS film as hole transporting layer.we fabricate ITO/ZC-NA/Sb₂S₃/PCPDTBT/PEDOT:PSS/Au with an efficiency up to 3.25%,and investigate the effects of polymer buffer layer and the crystallization temperature of Sb₂S₃ on device performance.Results demonstrate that the thermal annealing at 3000C produces the condense filling of crystalline Sb₂S₃ nanoparticles into ZC-NA for a better device performance,but the annealing at higher temperature?e.g.,350 ??leads to a poor filling of the Sb₂S₃ nanoparticles inside ZC-NA;moreover,the thickness of the polymer buffer layer imposes a remarkable influence on the device performance,and 40 nm is an optimal thickness for the buffer layer.It is found that the transport and collection of the charge carriers in the devices mainly depends on the intrinsic carrier mobilities in the polymer buffer layer;the photo-doping under illumination can increase the carrier mobilities in conjugated polymer films,which favors the carrier transport and collection and increases the contribution of photogenerated holes to photocurrent generation.