克服传输层瓶颈以从钙钛矿太阳能电池瞬态离子电流测量中量化离子参数
Overcoming Transport Layer Bottlenecks to Quantify Ionic Parameters from Transient Ion Current Measurements of Perovskite Solar Cells
AI总结：
本研究揭示传输层电容是钙钛矿太阳能电池瞬态离子电流测量量化离子密度的根本瓶颈，提出基于平均离子位移的校正及外推方法，以准确提取离子参数。
AI中文摘要：
在钙钛矿太阳能电池（PSCs）中，电压阶跃诱导的瞬态离子电流（TIC）测量，通常称为偏压辅助电荷提取（BACE），常被用于量化离子密度。漂移-扩散模拟预测，一旦可移动离子屏蔽钙钛矿中的电场，由TIC计算得到的离子密度将趋于饱和。然而，实验研究常报道的离子密度比该极限高出数个数量级，其物理起源在传输层（TL）性质方面仍未得到完全解释。本工作中，TLs的电容被确定为根本瓶颈：可量化的最大离子密度受限于可在钙钛矿/TL界面累积的电荷，因此TIC通常更强烈地依赖于TL性质而非钙钛矿的离子性质。通过系统改变C$_{\ m 60}$电子传输层厚度（p-i-n结构）和Spiro-OMeTAD空穴传输层掺杂（n-i-p结构）的实验证实了这种依赖关系在不同架构中的存在。为克服此限制，讨论了基于平均离子位移进行校正的重要性，并展示了如何将TL厚度趋势外推至无TL情形，从而根据所假设的离子模型，获得吸收层的实际离子电导率以及密度和迁移率。还考察了模拟情形，其中离子渗透入TLs或在正向偏压下的初始累积会提高电容极限并将TIC灵敏度扩展至更高离子密度。同时讨论了被捕获载流子的缓慢释放作为可能膨胀TIC信号的电流来源。总体而言，所呈现的分析为解释TIC及量化PSCs中离子性质提供了重要的实际考量。
英文摘要：
In perovskite solar cells (PSCs), voltage step-induced transient ion current (TIC) measurements, commonly referred to as bias-assisted charge extraction (BACE), are frequently used to quantify ion density. Drift-diffusion simulations predict that the ion density computed from TIC saturates once mobile ions screen the electric field in the perovskite. However, experimental studies often report ion densities orders of magnitude above this limit, whose physical origin remains incompletely explained in terms of transport layer (TL) properties. In this work, the capacitance of the TLs is identified to be the fundamental bottleneck: the maximum quantifiable ion density is limited to the charge that can accumulate at the perovskite/TL interfaces, so that TIC most often depends more strongly on TL properties than on the ionic properties of the perovskite. Experiments with systematically varied C$_{\rm 60}$ electron-TL thickness (p-i-n) and Spiro-OMeTAD hole-TL doping (n-i-p) confirm this dependence across architectures. To overcome this limitation, the importance of a correction based on the average ionic displacement is discussed, and it is shown how extrapolating the TL-thickness trend towards the TL-free situation yields the actual ionic conductivity of the absorber, alongside density and mobility, depending on the assumed ionic model. Simulations are also examined in which ion penetration into the TLs or initial accumulation under forward bias raise the capacitive limit and extend TIC sensitivity to higher ion densities. The slow release of trapped carriers is also discussed as a potential source of current which can inflate the TIC signal. Overall, the presented analysis provides important practical considerations for interpreting TIC and quantifying ionic properties in PSCs.
