Semitransparent Organic Solar Cells Enabled by a Sequentially Deposited Bilayer Structure

Semitransparent organic solar cells (ST-OSCs) have been regarded as a promising candidate for building integrated photovoltaics. In general, most of the ST-OSCs are based on a bulk heterojunction (BHJ) structure in which the morphology of the BHJ film must be delicately optimized. In this work, we introduce a sequentially deposited bilayer structure into ST-OSCs by using a PTB7-Th/IEICO-4F combination. The adoption of the bilayer structure not only simplifies the device optimization, but it is also found that, as the donor and the acceptor are separately deposited, the power conversion efficiency (PCE) of bilayer ST-OSCs can be improved by simply increasing the thickness of IEICO-4F, which has strong near infrared absorption but weak visible light absorption, without significantly affecting the average visible light transmittance (AVT) of the device. However, in the BHJ structure, the increase in BHJ film thickness unavoidably enhances the donor absorption in the visible light region, leading to a tradeoff between the PCE and AVT in BHJ-structured ST-OSCs. Eventually, the bilayer-structured device exhibits a better overall performance than the BHJ-structured device, e.g., a PCE of 8.5% for the bilayer structure versus a PCE of 8.1% for the BHJ structure with an AVT around 21%. Our findings indicate that the sequentially deposited bilayer structure, aside from its easy processing characteristics, also has great potential for preparing high-performance ST-OSCs.