Study Of The Effect Of Fabrication And Modulation Of NiO_x-Based Hole Transport Layers On Performance Of Perovskite Solar Cells

As a new type of energy technology,perovskite solar cells(PSCs)have huge research prospects and are currently the research focus in the field of renewable energy.One of the keys to improving the power conversion efficiency(PCE)of PSCs is to increase the utilization rate of photons convert into effective electrons,that is,to improve the charge extract and transport ability from the perovskite layer to the charge transport layer under the premise of ensuring high-quality perovskite films.Due to the high electrical conductivity,optical transmittance,good energy level matching with the perovskite layer,and excellent chemical stability,nickel oxide(Ni O_x)has become the very promising hole transport layers(HTLs)material with good research prospects.In order to enhance the efficiency of Ni O_x HTLs-based inverted planar PSCs,how to improve the hole transport ability of the Ni O_x HTLs has become the key and it is also the current research hotspot of Ni O_x HTLs.Since the crystalline quality,energy level matching and electrical conductivity of the HTLs are the main factors that determine the hole transport ability,the starting point of this thesis is improve the hole transport ability of Ni O_x HTLs.Firstly,a simple and effective low-temperature solution method is used to prepare Ni O_x HTLs and realize a high-efficiency perovskite solar cell device.Then the high-crystallinity Ni O_x films are prepared by pulsed laser deposition(PLD)technology and its growth mechanisms are clarified,and V_Ni defect regulation and Cu⁺ion dopants as an effective way to regulate energy levels and improve conductivity,which gradually boosts the PCE of PSCs.The main contents of this thesis are summarized as follows:(1)Synthesis of Ni O_x nanoparticle powder and preparation of Ni O_x HTLs by low-temperature solution method.Firstly,Ni O_x nanoparticle powder with uniform size is prepared by sol-gel method,and dissolved in deionized water to form a uniform dispersion,which is spin-coated and annealed at low temperature to obtain Ni O_x thin film.By changing the concentration of the Ni O_x nanoparticle dispersion,Ni O_x HTLs of different thicknesses were prepared,and the optimal perovskite solar cell efficiency reached 18.8%.(2)Fabricating the high-quality Ni O_x HTLs and clarifying the main factors affecting the growth of the film.PLD is one of the effective methods to prepare high-quality Ni O_xfilms.Laser energy,substrate temperature and oxygen partial pressure both have a great influence on the crystalline quality and V_Ni defects of the Ni O_x film.High laser energy guarantees good crystalline quality of Ni O_x film.As the substrate temperature raises,the crystallinity of Ni O_x film also increase due to the decrease of V_Ni defect contents.The oxygen partial pressure is higher,the more V_Ni defects exist in Ni O_x film.Moreover,the Cu⁺ions dopants occupy V_Ni defect sites of the Ni O_x lattice structure achieves the effect of improving the crystal quality and enhancing the mobility.(3)V_Ni defect regulation enhances the conductivity and optical transmittance of the Ni O_x HTLs,and promotes the hole extraction and transport.By simply adjusting the preparation parameters,including oxygen partial pressure,postannealing temperature,and duration time,the well-regulated V_Ni defects contribute to the modified conductivity and optical transmittance of the Ni O_x films.The conductivity and optical transmittance of Ni O_x films are all dramatically enhanced with the increasing oxygen partial pressure.Specifically,the valence band level of Ni O_x is adjusted by the V_Ni defect densities to better match or align with that of the perovskite layer for faster hole extraction with lower energy losses.Density functional theory calculation displays that the Fermi energy level is shifted to a lower energy level due to the enhanced hole carrier concentration generated from the increased V_Ni.Benefiting from the excellent optical transmittance,electronic conductivity,and well-matched energy alignment,the inverted PSCs with Ni O_x HTLs exhibit the highest PCE of 16.85%with high open-circuit voltage(1.14 V),short-circuit current density(20.49 m A/cm2),fill factor(0.72),and negligible current-voltage hysteresis effect.(4)Cu⁺ion dopants improve the conductivity of the Ni O_x HTLs and optimize the performance of perovskite solar cells.The Cu-doped Ni O_x with different doping concentrations was achieved by a hightemperature solid-state reaction,and Cu:Ni O_xfilms were prepared by PLD.Cu⁺ion dopants not only occupy the Ni vacancy sites to improve the crystallization quality and increase the hole mobility,but also substitute lattice Ni²⁺sites and act as acceptors to enhance the hole concentration.As compared to the undoped Ni O_x films,the Cu:Ni O_x films exhibit a higher electrical conductivity with a faster charge transportation and extraction for PSCs.By employing the prepared Cu:Ni O_x films as HTLs for the PSCs,a high photocurrent density of 23.17 m A/cm2 and a high power conversion efficiency of 20.41%are obtained,which are superior to those with physical vapor deposited Ni O_x HTLs.Meanwhile,the PSC devices show a very little hysteresis behavior and a long-term air-stability,even without any encapsulation.