Photoelectric Properties Of Cu₁₂Sb₄S₁₃ Quantum Dots As Hole Transport Layers In Perovskite Solar Cells

Perovskite solar cells?PSCs?have achieved the photovoltaic efficiency over 24%in recent years due to their high light absorption coefficient,wide absorption spectrum,high carrier mobility as well as the long charge diffusion length.However,the organic hole transporting layer?HTL?of spiro-OMeTAD commonly used in PSCs is complicated in preparation process,expensive,lower hole mobility,and the doping component is disadvantageous to the stability of the PSCs.Therefore,exploring new and inexpensive inorganic HTL is of great significance for enhancing the stability and reducing the cost of the PSCs.As a p-type ternary direct bandgap semiconductor,Cu₁₂Sb₄S₁₃ quantum dots?QDs?have excellent properties,such as non-toxicity,simple preparation process,tunable band gap and good stability,and there are two non-occupied states in the valence band,which contribute to a high hole mobility.Cu₁₂Sb₄S₁₃ QDs are considered to be the potential HTL for PSCs.In this thesis,Cu₁₂Sb₄S₁₃ QDs with different sizes are prepared by a thermolysis method.The phase,morphology and band structure of the QDs are characterized and their optical properties are measured.Cu₁₂Sb₄S₁₃ QDs are prepared as HTL to fabricate the PSCs.The charge transport mechanism and stability of Cu₁₂Sb₄S₁₃ QDs in PSCs are studied.The main research results and conclusions are summarized as follows:?1?Cu₁₂Sb₄S₁₃ QDs are prepared by a thermolysis method,and the effects of reaction temperature on the morphology,optical properties and band structure of the QDs are analyzed.It is found that the obtained product is a pure cubic phase Cu₁₂Sb₄S₁₃ QDs with good monodispersity.As the reaction temperature increases,the size of Cu₁₂Sb₄S₁₃ QDs increases from 4.5 nm to 7.9 nm,which is consisitent with the quantum confinement effect.The absorption onset in UV-vis spectra behaviors a red-shift phenomenon from 650 nm to 750 nm and the optical band gap decreases from 1.95 eV to 1.80 eV.The valence band of QDs moves toward the shallow level,and the conduction band moves toward the deep level.?2?The TiO₂ electron transport layer is prepared by hydrolysis method.When the concentration of TiO₂ precursor solution is 150 mM and the hydrothermal time is1 h,the photovoltaic performance is the best one.The perovskite grain size increases effectively by doping 5 wt%Pb?SCN?₂ into the perovskite precursor solution.By controlling the number of layers of QDs and the precursor solution concentration,the QDs film formation process is optimized.?3?Cu₁₂Sb₄S₁₃ QDs of different sizes are employed as HTL to fabricate the PSCs.The 5.7 nm sized Cu₁₂Sb₄S₁₃ QDs achieve the highest photovoltaic efficiency due to the most suitable energy level structure?14.13%?,and the corresponding photovoltaic efficiency of spiro-OMeTAD as HTL is 15.25%.In addition,the stability of PSCs using Cu₁₂Sb₄S₁₃ QDs as the inorganic HTL is effectively improved.The F4TCNQ doped QDs solution effectively increases the open-circuit voltage of the PSCs,and the final photovoltaic efficiency up to 14.37%.In summary,various sized Cu₁₂Sb₄S₁₃ QDs prepared by a multi-step thermolysis method are used as HTL to fabricate PSCs.Among them,the 5.7 nm sized Cu₁₂Sb₄S₁₃ QDs based PSCs achieve the comparable photovoltaic efficiency if compared with that of spiro-OMeTAD based PSCs and the stability is greatly improved.