Optimization Of Inverted Perovskite Solar Cells Based On Nickel Oxide Transport Layer

Perovskite solar cells have garnered significant attention from researchers due to their low production cost and simple manufacturing process,as well as their theoretical maximum energy conversion efficiency of 33%.After over a decade of research and development,inverted perovskite solar cells have achieved certified efficiencies exceeding 26%,approaching the highest certified efficiency of silicon solar cells at26.8%.Among various inorganic hole transport layer materials,nickel oxide is currently the most widely used foundation for perovskite solar cells,demonstrating laboratory efficiencies above 25%.The advantages nickel oxide as a hole transport layer include its low production cost,compatibility with diverse manufacturing processes,and excellent stability on both rigid and flexible substrates.Furthermore,nickel oxide-based hole transport layers exhibit promising potential for application in silicon/perovskite tandem solar cell devices and perovskite/perovskite tandem devices.This paper focuses on investigating inverted perovskite solar cells based on nickel oxide as the research subject.The specific research content includes:(1)In this study,we investigated the phenomenon of light soaking in laboratory-prepared nickel oxide-based inverted perovskite solar cells.The results from built-in potential measurements revealed that ion migration within the perovskite layer induced changes in the built-in potential and energy level distribution under certain bias voltages(including open-circuit illumination conditions).This subsequently altered the carrier recombination dynamics at the interface,leading to an increase in open-circuit voltage.Experimental results demonstrated that applying a specific intensity of forward bias pre-treatment significantly reduced the open-circuit voltage loss of the devices.During the light soaking process,the deepening of the reaction at the interface between nickel oxide and perovskite provides additional material sources for ion migration and light soaking.Based on these findings,we further examined the coexistence of low open-circuit voltage and high fill factor in current-voltage characteristics curves of the devices.Through investigations into carrier recombination dynamics and defect density at the nickel oxide/perovskite interface,numerous defect states were discovered to be present.The overall lower built-in electric field also played a significant role in causing a sharp decrease in photocurrent density at high bias voltages.Simulation experiments indicated that this phenomenon of low open-circuit voltage-high fill factor resulted from synergistic effects between high interfacial defect density and low built-in potential.The successful fabrication of high-efficiency battery devices requires simultaneous tuning of interface recombination,energy level alignment,and ion migration.(2)In order to address the issue of interface defects in nickel oxide-based inverted perovskite devices,we employed two approaches-buried interface modification and anti-solvent doping-to mitigate the defect density and enhance the photovoltaic performance of the devices.The facile solution preparation method is a prominent highlight and advantage of perovskite solar cells.However,spin-coating prepared perovskite/transport layer interfaces suffer from numerous defects that act as recombination centers for charge carriers,resulting in energy losses and reduced open-circuit voltage of the perovskite devices.Moreover,chemical reactions occurring at the nickel oxide/perovskite interface further exacerbate the defect density at the buried interface of perovskites.By introducing an organic barrier layer at this interface,we effectively reduced the defect density in perovskite films,suppressed non-radiative recombination between electrons and holes at interfaces,thereby improving open-circuit voltage of devices.Simultaneously,morphology of perovskite films was enhanced leading to increased short-circuit current density of devices.Furthermore,we investigated a small molecule doping strategy using anti-solvents as carriers to optimize device performance.The incorporation of dopants improved binding between lead iodide precursors with dimethyl sulfoxide,significantly altering morphology of polycrystalline perovskite films.Small molecule dopants exhibited homogeneous distribution throughout thin films and could penetrate into nickel oxide/perovskite interfaces during spin-coating process.Introduction of dopants not only improved open-circuit voltage and fill factor but also greatly enhanced stability of devices.(3)We investigated the impact of ambient humidity during nickel oxide preparation on the interface reaction between nickel oxide and perovskite,as well as its influence on functional modification at the monolayer level.The interaction between nickel oxide and perovskite is a significant source of interface defects and energy losses.By modifying the environmental humidity during the preparation process,it is possible to decrease the concentration of high-valence nickel ions in nickel oxide.This in turn results in a reduction of the reactivity of nickel oxide,thereby effectively suppressing interface reactions and minimizing both defect density and open circuit voltage losses.However,changes in nickel oxide composition led to a decrease in built-in potential within devices,limiting further enhancement of device efficiency.To address this issue,we employed self-assembled monolayers to adjust the Fermi level of nickel oxide and mitigate adverse effects caused by increased humidity-induced built-in potential drop.Our study revealed that an optimal level of humidity facilitated effective dipole formation at the surface of nickel oxide through enhanced hydroxyl groups under specific humidity conditions.By appropriately elevating the humidity during fabrication,the built-in potential of SAM-modified Ni O_x-based devices exhibited a remarkable increase.Attributable to the passivation effect and heightened dipole formation induced by the self-assembled monolayers,the energy conversion efficiency of the devices enhanced significantly,ascending from 17.44% to 20.23%.