An electron collection layer (ECL) between a photoactive overlay and an electrode plays a crucial role in optimizing the light field and charge extraction in bulk-heterojunction (BHJ) polymer solar cells (PSCs). However, the typical thickness of the photoactive layer is thinner than its optical path lengths, limiting further improvement of light absorption and device performance. Herein, we modulated the conjugated length of acetylacetonate-based ligands to synthesize a series of metal chelates [Hf(Acac)₄, Hf(ACB1)₄, and Hf(ACB)₄] and used them as light-scattering functionalized ECLs for PSCs. Benefitting from the strong and different self-assembly effects of these chelates, size-controllable nanoparticles were formed and well distributed on the entire surface of the photoactive layer, which acted as scattering centers to modulate the light field of the active layers effectively. Among these chelates, due to the most suitable aggregation size of Hf(ACB1)₄ nanoparticles, a preferable light-harvesting framework was achieved in PSCs using Hf(ACB1)₄ as ECL that eventually yielded a high PCE of >17%. Thus, our work demonstrates a flexible design strategy for obtaining a series of size-controllable metal chelates as efficient ECL for facilitating light trapping in PSCs.

光活性覆盖层和电极之间的电子收集层（ECL）在优化体异质结（BHJ）聚合物太阳能电池（PSC）中的光场和电荷提取方面起着至关重要的作用。然而，光敏层的典型厚度比其光程长度薄，从而限制了光吸收和器件性能的进一步改善。本文中，我们调节了基于乙酰丙酮化物的配体的共轭长度，以合成一系列金属螯合物[Hf（Acac）₄，Hf（ACB1）₄和Hf（ACB）₄]，并将它们用作PSC的光散射功能化ECL。得益于这些螯合物的强而不同的自组装效应，形成了尺寸可控的纳米颗粒，并在光敏层的整个表面上很好地分布，它们充当散射中心，可以有效地调制活性层的光场。在这些螯合物中，由于最合适的Hf（ACB1）₄纳米粒子聚集尺寸，在使用Hf（ACB1）₄作为ECL的PSC中实现了较好的光收集框架，最终产生了大于17％的高PCE。因此，我们的工作展示了一种灵活的设计策略，该策略可用于获得一系列尺寸可控的金属螯合物，作为有效的ECL，以促进PSC中的光捕获。