We studied three n-type polymers of the naphthalenediimide-bithiophene family as electron extraction layers (EELs) in hybrid perovskite solar cells. The recombination mechanism in these devices is found to be heavily influenced by the EEL transport properties. The maximum efficiency of the devices using the n-type polymers EELs did not exceed substantially that of the devices using PC 60 BM (about 11%), while a substantial improvement in their ambient stability (87% of the initial value after 270 minutes) compared to that using PC 60 BM (3.5% of the initial value after 270 minutes) was detected.Hybrid perovskites (HPs) are compounds with an ABX 3 perovskite structure, where A is an organic cation (CH(NH 2 ) 2+ or CH 3 NH 3 + ), B is a metal cation (Pb 2+ or Sn 2+ ) and X is a halide anion (Cl À , Br À and I À ). 1-3 These perovskite materials have ideal properties for photovoltaics, including high absorption coefficients (>10 4 cm À1 at 550 nm), 4,5 tuneable bandgaps (from 1.1 to 2.3 eV by altering their composition), 6,7 balanced charge transport and long carrier diffusion lengths (around 100 nm in CH 3 NH 3 PbI 3 and 1 mm in the CH 3 NH 3 PbI 3Àx Cl x lm). 8-10 In addition, these materials can be processed from solution, which makes them compatible with low cost and large-scale roll-to-roll fabrication techniques. Such advantageous features have intrigued the scientic community and triggered intensive research on HPs as light absorbers in photovoltaics (PV). During the past ve years, HP based solar cells (HPSCs) have witnessed a soaring increase in power conversion efficiency (PCE) from 3.8% to 20.1% through improvements in the device structure, 11-15 lm growth strategy, 16-27 lm composition, 2,3 and nature of the interfacial layers. [28][29][30][31][32][33] Despite such fundamental progress, challenges remain to be addressed in the development of hybrid perovskite solar cell technology. Primary among these is ensuring the stability and reproducibility of the solar cell performance and the possibility of increasing the PCE above 25%. Since the pioneering work by Miyasaka et al., the device structure of hybrid perovskite solar cells has been revolutionized, evolving from a liquid electrolyte based architecture, 11 to a solid state sensitized mesoscopic structure, 12 to meso-superstructured devices, and nally to planar structures. 13,14 Concurrently, the role of perovskites has evolved from a similedye to a semiconductor able to absorb light and to transport electrons and holes efficiently. At present, the most efficient HPSCs are based on a meso-superstructure and a planar device structure, which demonstrate comparable device performance (20.1 and 19.3%, respectively) due to the long diffusion length of electrons/holes and balanced charge transport. 25,33 However, these two structures are not equivalent, both from the perspective of processing and of exploitation of hybrid perovskite solar cells. The metal oxide scaffold (TiO 2 or Al 2 O 3 ) used in the meso-superstructured device geometry requires high si...

We have fabricated single crystal, thermally evaporated, and spin-coated thin-film transistors (TFTs) from the same organic semiconductor N,N′-1H,1H-perfluorobutyl dicyanoperylene carboxydiimide (PDIF-CN2) using various combinations of deposition methods and gate dielectrics to investigate how the charge transport properties vary with the degree of crystalline order. Never before has a semiconductor been studied in such a wide variety of processing methods, allowing cross-comparison of the microscopic factors influencing the charge transport, and in particular the trap density of states (DOS). Excellent transistor performance was achieved for PDIF-CN2 single crystals in combination with Cytop as a dielectric layer resulting in a mobility of up to 6 cm2/Vs, an on/off-ratio exceeding 108, and a subthreshold swing of 0.45 V/dec. Furthermore, gate-bias-stress effects are not present in these transistors and we observed low stress effects in the evaporated TFTs with Cytop as the gate dielectric. These findings are reflected in the trap DOS. The single crystal field-effect transistor with Cytop has a low trap DOS, whereas in evaporated TFTs, the trap DOS is higher by 2–3 orders of magnitude. Surprisingly, the trap DOS of the spin-coated TFT is similar to that in evaporated TFTs, except for additional discrete trap states centered around 0.24 eV below the conduction band.

High-performance n-type organic field-effect transistors were developed with ionic-liquid gates and N,N′′-bis(n-alkyl)-(1,7 and 1,6)-dicyanoperylene-3,4:9,10-bis(dicarboximide)s single-crystals. Transport measurements show that these devices reproducibly operate in ambient atmosphere with negligible gate threshold voltage and mobility values as high as 5.0 cm2/V s. These mobility values are essentially identical to those measured in the same devices without the ionic liquid, using vacuum or air as the gate dielectric. Our results indicate that the ionic-liquid and n-type organic semiconductor interfaces are suitable to realize high-quality n-type organic transistors operating at small gate voltage, without sacrificing electron mobility