通过时间分辨微波电导率重组动力学薄膜光伏材料
Summary
A Time Resolved Microwave Conductivity technique for investigating direct and trap-mediated recombination dynamics and determining carrier mobilities of thin film semiconductors is presented here.
Abstract
提出了一种用于研究在薄膜半导体光生电荷载体，特别是在光生伏打材料，如有机铅卤化物钙钛矿的重组动力学方法。钙钛矿薄膜的厚度和吸收系数最初特征在于轮廓和UV-VIS吸收光谱。两个激光功率和腔灵敏度的校准进行详细说明。一种用于执行闪光光解时间分辨微波电导率（TRMC）实验协议，确定材料的导电性的非接触方法，提出。一种用于通过执行TRMC微波频率的函数识别所述复合电导率的实部和虚部处理中给出。载流子动力学在不同的激励机制（包括功率和波长）决定。直接和陷阱介导的衰变过程区分技术进行介绍和讨论。结果被建模并且参考解释为在一个半导体光生电荷载体的一般动力学模型。所描述的技术适用于广泛的光电子材料，包括有机和无机光伏材料，纳米粒子，和导电/半导电薄膜。
Introduction
闪光光解时间分辨微波电导率（FP-TRMC）监视在NS-微秒时间尺度光激发载流子的动态，使之成为研究载流子复合过程的理想工具。理解的光诱导电荷载体的衰变机制薄膜半导体是具有关键的重要性的范围内的应用，包括光电装置的优化。诱导载流子寿命往往诱发载流子密度，激发波长，流动性陷阱密度和叠印率的功能。本文演示了时间分辨微波电导率（TRMC）技术的通用性调查范围广泛的载体动态依赖（强度，波长，微波频率）及其解释。
光生电荷可以修改以使用实际和材料的介电常数的虚数部分，这取决于它们的流动性和degre坐月子/本地化1电子。材料的导电性
正比于其复数介电常数
哪里
是微波电场的频率， 
和
是介电常数的实部和虚部。因此，导电性的实部相关介电常数的虚部，并且可以被映射到微波吸收，而导电性（以后称为极化）的虚部是与在谐振频率的偏移的微波场1。
利用微波功率，作为载流子动力学的探针的一个显著优点在于，以及监测的电荷载体，衰减机制衰减寿命/途径也可以被分析。
TRMC可以用来确定总的移动性3和生活荷载体的时间4。这些参数随后可用于直接和陷阱介导的重组机制3,5之间进行区分。这两个单独的衰减途径的依赖性可以定量分析作为载流子密度3,5和能量/波长5的功能。致载流子的本地化/约束可以通过比较电导率VS极化5（虚VS介电常数的实部）的衰变进行调查。
此外，也许是最重要的是，TRMC可用于表征其充当电荷载体衰减途径陷阱态。表面陷阱，例如，可从大容量陷阱由VS未钝化的样品6比较钝化区分开。亚带隙状态可以使用子带隙激发能5被直接影响。陷阱密度可以通过拟合TRMC数据7推断。
由于这种技术的通用性，TRMC已应用于研究广泛的材料，包括：传统的薄膜半导体如硅6,8和TiO 2 9，10，纳米粒子11，纳米管1中 ，有机半导体12，材料的共混物13，第 14，和混合光伏材料3，4，5。
为了获得使用TRMC定量信息，这是至关重要的，以便能够准确地确定数的吸收对于给定的光激发的光子。由于用于量化薄膜，纳米颗粒，溶液和不透明样品的吸收方法不同，这里介绍的样品制备和校准技术被用于薄膜样品而设计的。然而，提出了TRMC测量协议是很一般。
Protocol
Representative Results
Discussion
虽然TRMC技术可以提供丰富的光诱导左右电荷载体的动态信息，这是电导率的间接测量，因此护理需要解释结果时才能作出。所述TRMC技术测量总的移动性，并且不能用于电子和空穴的迁移率之间进行区分。其潜在的假定电导率正比于反射功率改变仅持有时变化小（<5％）16。此外，如果衰变过程中的共振频率的移位很大，则总（复）电导率将不得不被解构成其实部和虚部可被分?…
Disclosures
The authors have nothing to disclose.
Acknowledgements
Acknowledgment is made to the Australian Research Council (LE130100146, DP160103008). JAG is supported via an Australian Postgraduate Award, and DRM by an ARC Future Fellowship (FT130100214). We thank Nikos Kopidakis for helpful discussions.
Materials
| Hellmanex III detergent | Sigma Aldrich www.sigmaaldrich.com/catalog/product/sial/z805939?lang=en®ion=AU |
Z805939 | Corrosive and toxic. See SDS. |
| Lead (II) iodide (99%) | Sigma Aldrich www.sigmaaldrich.com/catalog/product/aldrich/211168?lang=en®ion=AU |
211168 | Toxic. See SDS |
| Anhydrous dimethylformamide (99.8%) | Sigma Aldrich www.sigmaaldrich.com/catalog/product/sial/227056?lang=en®ion=AU |
227056 | Toxic. See SDS |
| Anhydrous dimethylsulfoxide (99.9%) | Sigma Aldrich www.sigmaaldrich.com/catalog/product/sial/276855?lang=en®ion=AU |
276855 | Toxic. See SDS |
| Anhydrous 2-Propanol (99.5%) | Sigma Aldrich www.sigmaaldrich.com/catalog/product/sial/278475?lang=en®ion=AU&gclid= COnlgPaw780CFQZvvAod17EA4Q |
278475 | |
| Methylammonium iodide | Dyesol www.dyesol.com/products/dsc-materials/perovskite-precursors/methylammonium-iodide.html |
MS101000 | Also sold by Sigma Aldrich |
| Poly(methyl methacrylate) | Sigma Aldrich | 445746 | |
| Anhydrous chlorobenzene (99.8%) | Sigma Aldrich www.sigmaaldrich.com/catalog/product/aldrich/445746?lang=en®ion=AU |
284513 | Toxic. See SDS |
| Equipment | Company | Model | Comments/Description |
| UV-VIS-NIR spectrophotometer | Perkin-Elmer | Lambda 900 | |
| Profilometer | Veeco | Dektak 150 | |
| Vector Network Analyzer | Keysight www.keysight.com/en/pdx-x201927-pn-N9918A/fieldfox-handheld-microwave-analyzer-265-ghz?cc=US&lc=eng |
Fieldfox N9918A | |
| Tunable wavelength laser | Opotek www.opotek.com/product/opolette-355 |
Opolette 355 | |
| Neutral density filters | Thorlabs www.thorlabs.hk/newgrouppage9.cfm?objectgroup_id=3193 |
NUK01 | |
| Power meter | Thorlabs www.thorlabs.com/thorproduct.cfm?partnumber=PM100D |
PM100D | |
| Power sensor | Thorlabs www.thorlabs.com/thorproduct.cfm?partnumber=S401C |
S401C | |
| Cavity | Custom built | The cavity used in for this experiment was designed and built in-house. |
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