Vacuum Method Preparation And Characterization Of Antimoy Sulfide（Sb₂S₃） Planar Thin Film Solar Cells

The urgent need for high-efficiency and low-cost photovoltaics drives the sustained research on new absorber materials for thin-film photovoltaics.Copper indium gallium selenide,Cadmium Telluride and the organic-inorganic hybrid perovskite,the three leading players have respectively reached 22.6%,21%and 21.6%power conversion efficiencies.However,for the CIGS and CdTe system,it contains the scarcity materials of indium and gallium and toxic cadmium.And for hybrid perovskite system,it contains toxic lead in a highly soluble state and exhibits insufficient device stability,which might precludes their potential commercialization.Thus,a new stable and lead-free alternative would benefit sustainable use of solar energy and it is of great research importance.Antimony sulfide（Sb₂S₃）is appealing as a promising absorber due to its suitable bandgap（¹.7 eV）,strong light extinction coefficient(10⁵ cm^-1),binary compound,easy fabrication,earth-abundant and environment-friendly characters.In this work,we are aming to fabricate high efficiency and stable antimony sulfide thin film solar cell by rapid thermal evaporation（RTE）.The main contents of this thesis include:（1）Compact thin film of Sb₂S₃ as a promising absorber layer was obtained by RTE.The systematical characterizations of Sb₂S₃ film demonstrated the pure phase,void free and high crystallization.The large grain and preferential growth of Sb₂S₃ thin film were implemented by crystallization and cooling techniques,respectively.The corresponding devices were gradually optimized with a power conversion efficiency of³.5%,almost three times of planar devices fabricated by vacuum method.Both the non-oxide buffer layer（CdS layer）and free of hole transport layer enabled the high stability of the non-encapsulated planar devices.（2）Sb₂S₃ planar solar cells from evaporation method without hole-transport layer（HTM）assistance suffer from sulfur deficit vacancy and high back contact barrier.Herein,we developed a post-surface selenization treatment to Sb₂S₃ thin film in order to improve the device performance.The XRD,Raman and UV-vis spectra indicated the treated film kept the typical characters of Sb₂S₃.TEM/EELS mapping of treated Sb₂S₃ film revealed that only surface adjacent section was partly selenized and formed Sb₂(S_xSe_1-x)₃ alloy.In addition,XPS results further unfolded that there was trace selenium doping in the bulk of Sb₂S₃ film.The treated HTM-free Sb₂S₃ based solar cells were fabricated and an improved efficiency of 4.17%was obtained.After stored in ambient air for up to 100 days,the device could maintain 90%efficiency.Systematic materials and device characterizations were implemented to investigate the improvement mechanism for post-surface selenization.The back alloying could suppress the rear contact barrier to improve the fill factor and carrier extraction capability.The bulk Se-doping helped to passivate the interface and bulk defect so as to improve the CdS/Sb₂S₃ heterojunction quality and enhance the long-wavelength photon quantum yield.The robust treatment method with multifunctional effect holds great potential for new chalcogenide thin film solar cell optimization.（3）To increase the J_SC for Sb₂S₃ device,we demonstrate a combined Sb₂(S_xSe_1-x)₃/Sb₂S₃ structure for the device.By applying the low bandgap Sb₂(S_xSe_1-x)₃ alloy layer between the buffer layer and Sb₂S₃ absorber,the light absorption can extend into the near-infrared range.The large bandgap Sb₂S₃ layer can suppress the recombination at back electrode.Furthermore,an optimised composition of Sb₂(S_0.34Se_0.66)₃ is utilized to the CdS/Sb₂(S_0.34Se_0.66)₃/Sb₂S₃ solar cell.Our results show that the optimised device broaden the light absorption to 950 nm.The most efficient cell exhibits a short-circuit current density of 20.08 mA/cm²,an open circuit voltage of 0.51 V,and a fill factor of 57.34%,yielding a power conversion efficiency of 5.86%.All the solar cell parameters are the top value in the Sb-S-Se solar cells.This strategy could be easily extended to other chalcogenide thin film solar cells for the device performance improvement.（4）The large grain could minimize the grain boundary（GB）defect in the soalr cell.In this part,we fabricated amorphous Sb₂S₃ thin film,then utilized different post-treament to increase the film crystallinity.After selenization in the semi-closed condition,the grain size could reach 1 um,and the device performance was 4.27%.