Efficient semi-transparent organic solar cells toward building-integrated photovoltaics applications

Abstract

Renewable and cost-effective energy generation technology have been explored for decades owing to the foreseeable energy crisis and the occurred environmental pollution. As an application of photovoltaics (PV) technology, the building-integrated photovoltaics (BIPV) strategy paves a sustainable way to replace traditional building materials with solar cell modules, make the building itself as energy generator. The lightweight, flexibility and semi-transparency of organic solar cells (OSCs) make it applicative for semitransparent power-generating windows, remove the restriction of PV modules installation. OSCs have achieved remarkable progress in recent years, the power conversion efficiency (PCE) of the state-of-the-art OSC has been promoted to exceed over 18%, which is comparable to commercial silicon-based solar cells. Meanwhile, the PCE of semitransparent organic solar cells (STOSCs) have achieved over 12% with average visible transmittance (AVT) around 25%. Efficient STOSCs possess high light utilization efficiency(LUE) of near-infrared (NIR) and ultraviolet (UV) photons, and suitable balance between transparency and absorption in visible range. To realize the ultimate application of STOSCs, it is essential to develop both high-performance organic active materials with NIR absorption and stable transparent electrode with promise conductivity and high transmittance. Target power-generating windows in BIPV applications, we have conducted the following research projects to enhance both the electric and optical performance of STOSCs. 1. Demonstrate a self‐assembled and knitted Ag NPs/MWCNTs transparent top electrode with solution process We present a simple solution route to achieve Ag NPs/MWCNTs composite (AgCNTs) transparent and conductive film. The resultant AgCNTs film exhibits an extremely low sheet resistance of 14.5 Ω sq-1, an AVT of ~ 67% and a high color rendering index (CRI) of 97. The optimized device with solution-processed top transparent electrode achieves an AVT of 36% and a high CRI of 90. 2. Guided-growth ultrathin metal electrode to enhance light utilization efficiency of STOSCs We demonstrate a facile approach of introducing pre-located Ag nanoparticles (Ag NPs) with optimized amount of ligands to form high-quality and ultra-thin evaporated Ag film for high performance transparent electrode beyond those merely evaporated Ag electrodes. Fundamentally, our results show that, with the ligand-optimized Ag NPs, we can guide the growth of evaporated Ag clusters to form high quality transparent electrode. Equally important, the approach also reduce the defects of electron transport layer (ETL) and thus favor the carrier transportation/extraction to the electrode. As prepared film exhibit sheet resistance <15Ω sq-1 with AVT of 59.3%, and PM6:L8-BO based STOSC achieves light utilization efficiency (LUE) of 4.422% and power conversion efficiency of 12.80%. 3. Apply ternary active layer with improved charge transport and optical engineering in devices to achieve efficient STOSCs To optimize the optical and electric properties of active layer in STOSCs, a non-fused ring acceptor (BDC-4F-C8) by alkyl chain engineering is used as third component for ternary blend active layer. With optimizing the proportion of third component, STOSCs with ternary active layer perform improved open circuit voltage, short-circuit current and fill factor, which lead to best PCE of 13.19% with AVT of 24.56%, while the PCE of opaque one is17.02%. (499 words)