High Efficiency Transparent and Semi-Transparent Photovoltaics Based on a Layer-By-Layer Deposition

Transparent and semitransparent photovoltaics offer an exciting opportunity to integrate existing infrastructure with renewable energy. Organic photovoltaics (OPVs) are key enablers for wavelength-selective transparent photovoltaics (TPVs) because of their selective absorption in the near-infrared (NIR) that enables simultaneously high power conversion efficiency (PCE) and average visible transmittance (AVT). The recent rise of OPVs and TPVs has been accelerated in large part by the development of nonfullerene acceptors (NFAs) as highly adaptable deep NIR harvesting materials. Herein, sequential layer-by-layer (LBL) deposition of a selectively NIR absorbing nontraditional acceptor polymer is paired with a NIR absorbing donor IEICO-4F that is typically considered an NFA via solvent orthogonality. With detailed optimization of the active layers and top electrode, semi-transparent photovoltaics with a PCE of 8.8%, AVT of 40.9%, and a light utilization efficiency of 3.6% are demonstrated. The LBL approach enables explicit optical modeling of the device structure to extract exciton diffusion lengths >100 nm for both the polymer and IEICO-4F with a transition in charge collection length regimes dependent on the acceptor thickness. Furthermore, the LBL deposition technique enables an investigation of the full range of polymer thickness and its impact on power generation and optical performance.