A 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 low-crystallinity PL2 enables more 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%, retaining 90.23% of its optimal performance. In contrast, D18:L8-BO and PM6:L8-BO devices retain only 78.70% and 78.45% of their optimal PCEs, respectively. 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.