Low-Crystallinity Polymer Donor Enables High-Efficiency Semitransparent Organic Solar Cells under Substantial Donor Dilution

Abstract

Semitransparent organic solar cells (ST-OSCs) represent a promising technology for building-integrated photovoltaics and wearable electronics, yet achieving a balance between high power conversion efficiency (PCE) and average visible transmittance (AVT) remains challenging. Donor dilution is a common strategy to enhance AVT but often leads to severe PCE loss due to reduced donor-acceptor interfacial areas and impaired charge transport. Here, we demonstrate that employing a low-crystallinity polymer donor (PL2) significantly mitigates performance degradation under high donor dilution conditions. Compared to highly crystalline donors (D18 and PM6), the amorphous PL2 enables homogeneous dispersion in the L8-BO acceptor matrix, preserving efficient charge generation and collection even at a D:A ratio of 1:4. The PL2:L8-BO-based device maintains a PCE of 15.16% outperforming D18-(15.04%) and PM6-based (15.00%) systems. By leveraging this approach, we fabricate ST-OSCs with a light utilization efficiency (LUE) of 4.34%. This work highlights the critical role of donor crystallinity control in developing high-performance ST-OSCs and provides a practical material design strategy for transparent photovoltaics.