Materials Department, University of California Santa Barbara , Santa Barbara, California 93106, United States.
National Renewable Energy Laboratory (NREL) , Golden, Colorado 80401, United States.
ACS Appl Mater Interfaces. 2017 Jun 7;9(22):19021-19029. doi: 10.1021/acsami.7b03529. Epub 2017 May 22.
Many high efficiency organic photovoltaics use fullerene-based acceptors despite their high production cost, weak optical absorption in the visible range, and limited synthetic variability of electronic and optical properties. To circumvent this deficiency, non-fullerene small-molecule acceptors have been developed that have good synthetic flexibility, allowing for precise tuning of optoelectronic properties, leading to enhanced absorption of the solar spectrum and increased open-circuit voltages (V). We examined the detailed morphology of bulk heterojunctions of poly(3-hexylthiophene) and the small-molecule acceptor HPI-BT to reveal structural changes that lead to improvements in the fill factor of solar cells upon thermal annealing. The kinetics of the phase transformation process of HPI-BT during thermal annealing were investigated through in situ grazing incidence wide-angle X-ray scattering studies, atomic force microscopy, and transmission electron microscopy. The HPI-BT acceptor crystallizes during film formation to form micron-sized domains embedded within the film center and a donor rich capping layer at the cathode interface reducing efficient charge extraction. Thermal annealing changes the surface composition and improves charge extraction. This study reveals the need for complementary methods to investigate the morphology of BHJs.
许多高效率的有机光伏器件使用富勒烯基受体，尽管它们的生产成本高、可见光范围内的光吸收弱以及电子和光学性质的合成可变性有限。为了规避这一缺陷，已经开发出了非富勒烯小分子受体，它们具有良好的合成灵活性，允许对光电性质进行精确调整，从而增强对太阳光谱的吸收并提高开路电压（V）。我们研究了聚（3-己基噻吩）和小分子受体 HPI-BT 的体异质结的详细形态，揭示了导致太阳能电池填充因子在热退火时提高的结构变化。通过原位掠入射广角 X 射线散射研究、原子力显微镜和透射电子显微镜研究了 HPI-BT 在热退火过程中相转变过程的动力学。HPI-BT 受体在薄膜形成过程中结晶，形成嵌入薄膜中心的微米级域和在阴极界面处富施主的覆盖层，从而降低有效的电荷提取效率。热退火会改变表面成分并改善电荷提取。这项研究揭示了需要互补的方法来研究 BHJ 的形态。
