Record power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have been obtained with the organic hole transporter 2,2′,7,7′-tetrakis( N , N -di- p -methoxyphenyl-amine)9,9′-spirobifluorene (spiro-OMeTAD). Conventional doping of spiro-OMeTAD with hygroscopic lithium salts and volatile 4- tert -butylpyridine is a time-consuming process and also leads to poor device stability. We developed a new doping strategy for spiro-OMeTAD that avoids post-oxidation by using stable organic radicals as the dopant and ionic salts as the doping modulator (referred to as ion-modulated radical doping). We achieved PCEs of >25% and much-improved device stability under harsh conditions. The radicals provide hole polarons that instantly increase the conductivity and work function (WF), and ionic salts further modulate the WF by affecting the energetics of the hole polarons. This organic semiconductor doping strategy, which decouples conductivity and WF tunability, could inspire further optimization in other optoelectronic devices.

Conducting polymers, such as the p-doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), have enabled the development of an array of opto- and bio-electronics devices. However, to make these technologies truly pervasive, stable and easily processable, n-doped conducting polymers are also needed. Despite major efforts, no n-type equivalents to the benchmark PEDOT:PSS exist to date. Here, we report on the development of poly(benzimidazobenzophenanthroline):poly(ethyleneimine) (BBL:PEI) as an ethanol-based n-type conductive ink. BBL:PEI thin films yield an n-type electrical conductivity reaching 8 S cm⁻¹, along with excellent thermal, ambient, and solvent stability. This printable n-type mixed ion-electron conductor has several technological implications for realizing high-performance organic electronic devices, as demonstrated for organic thermoelectric generators with record high power output and n-type organic electrochemical transistors with a unique depletion mode of operation. BBL:PEI inks hold promise for the development of next-generation bioelectronics and wearable devices, in particular targeting novel functionality, efficiency, and power performance.

Reducing interface nonradiative recombination is important for realizing highly efficient perovskite solar cells. In this work, we develop a synergistic bimolecular interlayer (SBI) strategy via 4-methoxyphenylphosphonic acid (MPA) and 2-phenylethylammonium iodide (PEAI) to functionalize the perovskite interface. MPA induces an in-situ chemical reaction at the perovskite surface via forming strong P-O-Pb covalent bonds that diminish the surface defect density and upshift the surface Fermi level. PEAI further creates an additional negative surface dipole so that a more n-type perovskite surface is constructed, which enhances electron extraction at the top interface. With this cooperative surface treatment, we greatly minimize interface nonradiative recombination through both enhanced defect passivation and improved energetics. The resulting p-i-n device achieves a stabilized power conversion efficiency of 25.53% and one of the smallest nonradiative recombination induced V_oc loss of only 59 mV reported to date. We also obtain a certified efficiency of 25.05%. This work sheds light on the synergistic interface engineering for further improvement of perovskite solar cells.

Recently, flexible transparent electrodes (FTEs) have attracted extensive attention as an essential element for future organic electronics (OEs), i.e. solution-processable, scalable and flexible organic electronics (FOEs). Although the traditional transparent electrode indium tin oxide (ITO) has been widely used in OEs, its brittleness and high cost significantly limit its application in the next generation of devices, typically flexible electronics. Thus, many alternatives, such as graphene, carbon nanotubes, conductive polymers, metal nanowires, metal grids and electrospun metallic nanofibers, have arisen at the forefront of FTEs. Among them, silver nanowire (AgNW) networks have attracted particular attention due to their excellent electrical conductivity and high transmittance, as well as facile availability and low cost. Since many studies on AgNWs have been published, a comprehensive review highlighting the advantages of AgNWs in FOEs is highly required. In this review, the synthesis and film fabrication of AgNWs have been firstly summarized, focusing especially on the properties of conductivity and light transmittance. Next, post treatments with different approaches to improve the conductivity of AgNWs have been included. And then, characterization of FTEs has been introduced with details on key parameters for FOEs. Furthermore, AgNW-based FOEs have been summarized to demonstrate the recent progress, such as organic light-emitting diodes (OLEDs), organic solar cells (OSCs), light-emitting electrochemical cells (LECs), organic field effect transistors (OFETs), organic memory devices (OMDs), etc. Finally, perspectives for AgNWs in FOEs have been discussed and concluded as well. It is expected that AgNWs could be the focus of future FOEs compared with other alternatives in terms of their advantages of optoelectronic properties, film-formation, solution-processability and flexibility.