Tetraphenylphosphonium Bromide as a Cathode Buffer Layer Material for Highly Efficient Polymer Solar Cells

Abstract

Here, we introduced the role of small organic molecule tetraphenylphosphonium bromide (QPhPBr) as an electron-transporting layer (ETL) material for fabricating high-efficiency bulk heterojunction polymer solar cells (PSCs). Their significantly higher power conversion efficiency (PCE) in well-known active layer devices (PTB7-Th:PCBM, PBDTTT-CT:PCBM, and P3HT:PCBM) was observed compared to that of the bare Al cathode. The use of N719 as an ETL was also demonstrated. Observed data reveal that QPhPBr-based devices exhibit high PCEs up to 9.18, 8.42, and 4.81% from PTB7-Th, PBDTTT-CT, and P3HT, respectively. For comparisons, the bare Al devices show PCEs of 5.37, 4.75, and 3.01%, respectively. Moreover, further enhancement of PSC efficiency (9.83, 8.69, and 5.35%) is achieved from mixed binary solution of N719:QPhPBr because of modulated adjustment of the work function of the Al electrode. Our results indicate the excellent function of tetraphenylphosphonium bromide and its binary blend as effective small-molecule organic materials to regulate the metal surface properties and the potential used as excellent cathode buffer layer materials for realizing high-efficiency PSCs.

An Ultraviolet‐Deposited MoO3 Film as Anode Interlayer for High‐Performance Polymer Solar Cells

“…Compared with the bare ITO‐based device, the control device with PEDOT:PSS anode interlayer displays significantly better photovoltaic performance with V oc , J sc , FF and PCE of 0.913 V, 14.56 mA cm −2 , 68.83%, and 9.15%, respectively, resulting from the improved work function and interface properties of the PEDOT:PSS‐modified ITO. In addition, the control device with PEDOT:PSS anode interlayer in this work also shows slightly better photovoltaic performance when compared with the similar PBDB‐T:ITIC‐based devices (PCE = 8.84%) reported by Zhan and coworkers39 Furthermore, the device based on the MoO 3 anode interlayer exhibits a similar V oc of 0.911 V, a larger J sc of 15.12 mA cm −2 , and a slightly lower FF of 67.33%, and eventually obtains a higher PCE of 9.27%, in comparison with the ITO/PEDOT:PSS‐based device. ITO/MoO 3 (ITO modified by the MoO 3 anode interlayer) with appropriate work function as well as smooth and relatively hydrophobic surface can provide excellent energy level alignment and interface contact with active layer and thus enable efficient holes extraction from active layer to ITO anode, which contribute to the best photovoltaic performance of the ITO/MoO 3 ‐based device than those of the bare ITO‐based device and ITO/PEDOT:PSS‐based device.…”

Role of Central Metal Ions in 8‐Hydroxyquinoline‐Doped ZnO Interfacial Layers for Improving the Performance of Polymer Solar Cells

“…Major benefits of OSCs include potentially low cost, compatibility with large‐area production methods, a lightweight structure, and a relatively short energy payback time . Previous studies have conducted the intensive research to extend the OSCs absorption range by modifying their photoactive layer, which has comprised highly functional novel donor, and the acceptor materials . New interfacial device architectures with appropriate doping materials have been explored for future commercial applications …”

“…Organic materials with suitable electrical and optical properties contribute to the scalability of OSC features . The cathode interfacial materials play a critical role in circumventing the shortcomings of the cathode transport layer (CTL), such as instability, low charge transportation, and weak physical contact . To improve the OSC performance, interfacial materials are placed between the photoactive layer and the electrodes.…”

“…The proper modulating energy‐level alignments between the lowest unoccupied molecular orbital (LUMO) of the acceptor in the photoactive layer and the conduction band of the CTL (or Fermi level of the metal cathode) are important. In addition, modulating energy‐level alignments between LUMO, CTL, and the presence of a deep highest occupied molecular orbital (HOMO) energy level for blocking the mobile holes are important . Additionally, either a large number of excitons must be produced in the photoactive layer or a large number of charge carriers must be collected from the electrodes (or both) before recombination the device under sunlight illumination .…”

“…However, poor interfacial contact with the hydrophilic organic layer and surface defects may limit the device's power conversion efficiency (PCE) . Few novel examples of the developed CTL materials, namely perylene bisimide (PBI)‐H‐ZnO, fluorinated copper‐phthalocyanine, tetraphenylphosphonium bromide, W 18 O 49 nanowires, 8‐hydroquino‐latolithium, perylene diimides, pyridinium salts, graphene quantum dots, metallophthalo‐cyanine, DNA, and TiO 2 :polyethylenimine (PEI), have been used as the interfacial layers to facilitate the fabrication of high‐efficient OSCs. Alternative passivation methodology to fabricate high‐performance OSCs has a sandwich structure between the CTL and the photoactive layer such as ultrathin dielectric (Al 2 O 3 and ZrO 2 ) layers using atomic layer deposition route and carbon dots .…”