In photovoltaic cells, increasing the light absorption coefficient enhances the photocurrent and quantum efficiency of the cell. Here, we report an efficient approach that enhances light absorption by changing the crystal phase of an evaporated ZnPc film on indium tin oxide (ITO) substrates. Under thermal treatment (>200 °C), the crystal phase of ZnPc changed from metastable α-ZnPc to stable β-ZnPc. We tested and compared the effects of this phase transition on the donor film of organic photovoltaic (OPV) cells. After treating the β-ZnPc film at 220 °C, the short-circuit current of the OPV was improved from 2.58 to 3.40 mA/cm², and the quantum efficiency was improved from 650 to 750 nm. Moreover, on a copper iodide (CuI)–ITO substrate, the ZnPc molecules were precisely controlled in the lying-down orientation. With their lying-down orientations, the light absorbance capacities of the metastable α-ZnPc phase and stable β-ZnPc phase (annealed at 300 °C) were 1.3- and 1.5-fold higher, respectively, than that of metastable α-ZnPc standing upright on the ITO substrate. This work provides a fundamental understanding of the crystal phases and orientation changes of the ZnPc molecules, enabling maximization of the light absorption coefficient and the design of efficient small-molecule OPV cells.

中文翻译：

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高效结晶有机光伏的晶相和蒸发锌酞菁薄膜的取向

在光伏电池中，增加光吸收系数可增强电池的光电流和量子效率。在这里，我们报告了一种有效的方法，该方法可通过改变铟锡氧化物（ITO）衬底上蒸发的ZnPc膜的晶相来增强光吸收。在热处理（> 200°C）下，ZnPc的晶相从亚稳态的α-ZnPc变为稳定的β-ZnPc。我们测试并比较了此相变对有机光伏（OPV）电池供体膜的影响。在220°C下处理β-ZnPc膜后，OPV的短路电流从2.58提高到3.40 mA / cm ²，并且量子效率从650nm提高到750nm。此外，在碘化铜（CuI）-ITO衬底上，ZnPc分子在躺下方向上受到精确控制。在其躺下的取向下，亚稳态α-ZnPc相和稳定的β-ZnPc相（在300°C退火）的光吸收能力分别比亚稳态α-ZnPc固定的高1.3倍和1.5倍。垂直放置在ITO基板上。这项工作提供了对ZnPc分子的晶相和取向变化的基本了解，从而使光吸收系数最大化并设计了有效的小分子OPV电池。