Study On The Construction And Properties Of Perovskite Solar Cells Based On NiCo₂O₄ Hole Transport Layers

In the past ten years,perovskite solar cells（PSCs）have attracted much attention due to their outstanding performance.Perovskite solar cells have the advantages of high photoelectric conversion efficiency,low material cost,and solution preparation.The power conversion efficiency of PSCs has increased from 3.8%to 25.5%,and perovskite solar cells have become the most promising solar cells.In general,the structures of PSCs mainly have formal（n-i-p）and inverted（p-i-n）.In an inverted structure,hole transport layers（HTLs）play an important role in transporting holes and blocking electrons,not only affecting the power conversion efficiency of PSCs,but also significantly affecting the working stability of PSCs.Therefore,choosing suitable HTLs are critical to construct PSCs.Nickel cobaltate（NiCo₂O₄）,as a p-type hole semiconductor material,is widely used in various fields because of its low material price,high electrical performance and facile preparation process.This paper studies the performance of perovskite solar cells with NiCo₂O₄ as the hole transport layer.The main research contents are as follows:（1）NiCo₂O₄ was prepared on a conductive glass substrate（FTO）by a simple hydrothermal method.And by adjusting the synthesis time to 90min,120min and 150min,the NiCo₂O₄ with different morphologies were obtained.They are nanosheets（NSs）,nanosheets-wires（NS-NWs）and nanowires（NWs）,respectively.The electrical performance measurements indicate that NiCo₂O₄NWs has higher conductivity and hole mobility,which is conducive to assemble high-performance PSCs.Subsequently,PSCs with the structure of FTO/NiCo₂O₄/CH₃NH₃Pb I₃/PC₆₁BM/Ag were constructed,and the effects of NiCo₂O₄ NSs,NS-NWs,and NWs as HTLs on the performance of PSCs were studied respectively.The results show that the perovskite films based on NiCo₂O₄ with different morphologies exhibit similar morphology and crystallinity,while the devices assembled by NWs have more excellent hole extraction capabilities,lower defect state density and charge transfer resistance,and higher hole recombination resistance.Therefore,the NWs device achieve the champion efficiency of 11.58%.In addition,after the devices based on NSs,NS-NWs and NWs are stored in an environment with a relative humidity at 40±5%for 10 days,the efficiency of all maintained more than 80%of the initial efficiency.（2）In order to improve the performance of NiCo₂O₄ NWs devices,Zn ions were introduced to replace part of Ni ions in NiCo₂O₄ NWs,and a Zn_xNi_1-xCo2O4（x=0.05,0.1,0.15,0.2）hole transport layer was successfully prepared.The experimental results show that the morphology and optical transmittance of NiCo₂O₄ NWs are related to the amount of Zn²⁺.When the doping amount of Zn²⁺is 0.15 and 0.2 respectively,the optical transmittance is low（less than 70%in the visible light region）,which cannot meet the requirements for preparing high-efficiency PSCs.In addition,the conductivity and hole mobility results show that the improvement effect of 0.05 Zn²⁺doping on the conductivity and hole mobility is not as good as 0.1 Zn²⁺doping.Therefore,we choose the NiCo₂O₄ NWs with a Zn²⁺doping amount of 0.1（Zn-0.1）as HTLs to construct PSCs,and study the effect on device performance.The results show that,compared with the undoped NWs,the conductivity and hole mobility of Zn-0.1 are significantly improved,which enables the hole extraction and transport,and decrease the defect density and charge transport resistance of Zn-0.1NWs devices.In addition,the performance of perovskite films deposited on Zn-0.1 has been improved.Therefore,the power conversion efficiency of PSCs based on Zn-0.1 NWs is increased to 13.41%.（3）For further to improve the device performance,we introduced NH₄F as an interface modification material between the interface of Zn-0.1 and perovskite layer.The results indicate that with NH₄F modification,the perovskite layer have a better morphology with improved light absorption capacity.The defects between the interface have been effectively passivated and thereby reduce the charge transport resistance and recombination of electrons and holes.Therefore,the power conversion efficiency of the devices is up to 14.88%with an improved performance.In addition,the stability of the device has been improved thanks to the introduction of the NH₄F.After the devices are stored for 10 days under a relative humidity of 40±5%,its efficiency is close to 90%of the initial efficiency.In this paper,a simple hydrothermal synthesis method was used to prepare NiCo₂O₄ with different morphologies and used in HTLs for PSCs,which provides a direction and reference for exploring new and low-cost HTMs.