表面粗糙度对薄膜太阳能电池光电特性测量的影响
Impact of Surface Roughness in Measuring Optoelectronic Characteristics of Thin-Film Solar Cells
AI总结：
研究薄膜太阳能电池表面粗糙度对光电特性测量的影响，提出掠射角聚焦离子束抛光技术降低CdTe表面粗糙度，实现高分辨率光电特性测量。
摘要：
薄膜吸收层的微观结构特性在开发高性能太阳能电池中起着至关重要的作用。扫描探针显微镜常用于测量薄膜太阳能电池的空间不均匀特性。虽然功能强大，但纳米级探针对样品的粗糙度敏感，会将混合信号和意外伪影引入测量中。在此，我们应用掠射角聚焦离子束（FIB）技术来降低CdTe的表面粗糙度，同时保留太阳能电池的次表面光电特性。我们比较了FIB抛光前后的纳米级光电特性。同时收集的开尔文探针力显微镜（KPFM）和原子力显微镜（AFM）图像显示，CdTe原始状态（峰谷粗糙度约600纳米）的接触电势差（CPD）遵循地形分布。而抛光后的CdTe（粗糙度约20纳米）的CPD图独立于表面粗糙度。我们证明平滑的CdTe表面也使分辨率远小于单个晶粒（<1微米）的高分辨率光致发光（PL）成像成为可能。我们的时域有限差分（FDTD）仿真说明了局部光激发如何与CdTe表面相互作用。我们的工作支持低角度FIB抛光可以在研究薄膜太阳能电池的埋藏次微观结构特性方面有益，但需注意表面附近可能的离子束损伤。
英文摘要：
Microstructural properties of thin-film absorber layers play a vital role in developing high-performance solar cells. Scanning probe microscopy is frequently used for measuring spatially inhomogeneous properties of thin-film solar cells. While powerful, the nanoscale probe can be sensitive to the roughness of samples, introducing convoluted signals and unintended artifacts into the measurement. Here, we apply a glancing-angle focused ion beam (FIB) technique to reduce the surface roughness of CdTe while preserving the subsurface optoelectronic properties of the solar cells. We compare the nanoscale optoelectronic properties before and after the FIB polishing. Simultaneously collected Kelvin-probe force microscopy (KPFM) and atomic force microscopy (AFM) images show that the contact potential difference (CPD) of CdTe pristine (peak-to-valley roughness of approximately 600 nm) follows the topography. In contrast, the CPD map of polished CdTe (roughness of approximately 20 nm) is independent of the surface roughness. We demonstrate the smooth CdTe surface also enables high-resolution photoluminescence (PL) imaging at a resolution much smaller than individual grains (< 1 micrometer). Our finite-difference time-domain (FDTD) simulations illustrate how the local light excitation interacts with CdTe surfaces. Our work supports low-angle FIB polishing can be beneficial in studying buried sub-microstructural properties of thin-film solar cells with care for possible ion-beam damage near the surface.
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