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Narrow band-gap conjugated polyelectrolytes (NBGCPs) combine the advantages of narrow band-gap conjugated polymers and polyelectrolytes. However, they are limited reported and seldom used in polymer solar cells (PSCs). Herein, we design and synthesized two PTB7-based NBGCPs, cationic PTB7-NBr and zwitterionic PTB7-NSO 3 , as cathode interlayers (CILs) in conventional PSCs. Compared to poly[4,8-bis(2-ethylhexyloxyl)benzo[1,2- b :4,5- b′ ]dithiophene-2,6-diyl- alt -ethylhexyl-3-fuorothithieno[3,4- b ]thiophene-2-carboxylate-4,6-diyl] (PTB7), both PTB7-NBr and PTB7-NSO 3 have similar absorption while PTB7-NBr has a higher HOMO level than PTB7 and PTB7-NSO 3 . With PTB7-NBr and PTB7-NSO 3 as CIL and Al as cathode, the devices both exhibited high efficiencies. The optimal power conversion efficiencies (PCEs) of PTB7-NBr device and PTB7-NSO 3 device are about 9%. However, PTB7-NBr devices are less sensitive to the CIL film thicknesses and the PCEs of PTB7-NSO 3 device decrease sharply when the thickness of PTB7-NSO 3 over 3 nm. What's more, when the devices with an Ag cathode PTB7-NBr exhibits a much better interfacial modification than PTB7-NSO 3 . Ultraviolet photoelectron spectroscopy (UPS) indicate that the work functions of PTB7-NBr and PTB7-NSO 3 film on Al are identical while on Ag they are different. We suggest the insensitivity to CIL thickness and good performance for Ag device of PTB7-NBr devices are attributed to the bromide anions in PTB7-NBr. The report on PTB7-based NBGCPs broads the types of organic cathode interfacial materials and is beneficial to the deep insight of ionic effect in electrolyte materials. [ABSTRACT FROM AUTHOR]

Two star-shaped oligofluorenes with hexakis(fluoren-2-yl)benzene as core are designed and synthesized, namely Tn0 and Tn1. Diethylamino groups are attached to the side chain of fluorene units of Tn0 and Tn1 and enable them alcohol solubility, additional hydrophobic nhexyl chains are grafted on the π-extended fluorene arms of Tn1. Power conversion efficiency (PCE) as high as 8.62% and 8.80% are achieved when utilizing Tn0 and Tn1 as cathode interlayers in inverted polymer solar cells, respectively. The work function of ITO effectively decreased by introducing interlayer, resulting in high Voc of the device, besides, the wetting properties of the interlayers can be tuned by modifying the oligofluorenes with π-extended structure, and the more hydrophobic interlayer will benefit the device performance with enhanced Jsc and FF. [ABSTRACT FROM AUTHOR]

Planar heterojunction perovskite solar cells were fabricated through a low temperature approach. We find that the device performance significantly depends on the external bias before and during measurements. By appropriate optimization of the bias conditions, we could achieve an 8-fold increase in the power conversion efficiency. The significant improvement in device performance might be caused by the ion motion in the perovskite under the external electric field. [ABSTRACT FROM AUTHOR]

A new carboxylate functionalized small molecule non-conjugated zwitterion, HDAC was proposed for its feasible one-step synthetic procedure. It can be used as an efficient interlayer to improve the fullerene/cathode interface of inverted planar heterojunction perovskite solar cells. A HDAC modified device could increase the power conversion efficiency from 15% to 17%. The main increase of the performance parameter lies on the increase of fill factor from around 72% to 80%, which could be attributed to the formation of interface dipole and elimination of potential barrier at the interface of electron transporting layer and cathode. This work brings up a simple design principle for efficient interfacial materials in perovskite solar cells. [ABSTRACT FROM AUTHOR]

Hybrid organic/inorganic perovskite planar heterojunction (PHJ) solar cells are becoming one of the most competitive emerging technologies. Here, the devices (ITO/PEDOT:PSS/CH 3 NH 3 PbI 3− x Cl x /PC 60 BM/C 60 /Al) are fabricated based on solution process. A power conversion efficiency (PCE) up to 13.1% was obtained after isopropanol (IPA) solvent treatment, which was 9% improvement than that of the original devices. Photocurrent hysteresis could be reduced to a certain extent by introducing IPA treatment. Solvent treatment can remove as-grown impurities like CH 3 NH 3 I and defects formed during the device fabrication. We also demonstrated the electrical and optical properties of perovskite films were improved. The addition of IPA-treated facilitates the formation of a relatively smooth PC 60 BM films. This work provides a very simple but effective strategy to enhance the power conversion efficiency of perovskite solar cells. [ABSTRACT FROM AUTHOR]

The solution-processable electron transport layer (ETL) is essential for the electron transport and extraction of inverted perovskite solar cells (PSCs). A new naphthalene diimide based copolymer with phosphite ester pendants (PFNDI) is developed as an ETL in inverted PSCs. The naphthalene diimide backbone and the phosphite ester pendants endow PFNDI a good electron transport property and a strong binding force on perovskite. By introducing PFNDI on the perovskite interface, we succeed in improving surface morphologies of perovskite film, reducing the trap density and facilitating electron transport properties. The PFNDI-based devices exhibit an optimal power conversion efficiency of 18.25% (with the V OC = 1.068 V, J SC = 22.53 mA cm−2 and FF = 75.85%) and fine long-term stabilities. The un-encapsulated PFNDI-based devices maintain 80% of their initial performance after storage for more than 500 h at 20 °C in air with a relative humidity of 25% and 75% of their initial efficiency after continuously heating for about 300 h. Our work demonstrated that NDI-based polymers with proper pendant groups can be the ideal n-type organic materials for high-performance PSCs. Image 1 • A new naphthalene diimide based copolymer was synthesized and introduced into PSCs. • The copolymer improves the charge transport properties to deliver a PCE of 18.25%. • Our findings may pave a new way to design promising non-fullerene-based ETL. [ABSTRACT FROM AUTHOR]