Low Temperature Sequential Deposition Strategy for High Performance Pseudoplanar Heterojunction Semitransparent Organic Photovoltaics

Abstract Semitransparent organic photovoltaics (ST‐OPVs) have great application potential in photovoltaic buildings and wearable devices. Studies have proved that power conversion efficiency (PCE) and average visible transmittance (AVT) reveal more balanced in pseudoplanar heterojunction (PPHJ) structure than in bulk heterojunction (BHJ) structure. An interesting approach named low temperature sequential deposition (LTSD)—spin‐coating the small molecule acceptor (A) Y6 on polymer donor (D) PM6—is proposed to form an efficient PPHJ structure. In the LTSD process, small molecule Y6 will diffuse through amorphous PM6 layer which means that Y6 finally aggregates at the bottom of active layer and results in vertical gradient concentration distribution. In this structure, adjustment of D:A ratio can achieve higher AVT with maintaining less PCE loss compared with BHJ structure. The fabricated LTSD devices provide PCE of 12.36% (AVT of 23.19%) at 45:40 nm (D:A layer thickness) and PCE of 11.26% (AVT of 25.10%) at 40:40 nm (D:A), while BHJ devices provide PCE of 11.43% (AVT of 21.32%) at 85 nm (D:A = 1:1.2 w). Besides, the LTSD devices are more stable than BHJ devices due to smoother surface. LTSD strategy provides a new approach for achieving PPHJ structure and high‐performance ST‐OPVs.