Robert S. Gurney

Sodium bromide additive improved film morphology and performance in perovskite light-emitting diodes

Organometal halide perovskite is a promising material to fabricate light-emitting diodes (LEDs) via solution processing due to its exceptional optoelectronic properties. However, incomplete precursor conversion and various defect states in the perovskite light-emitting layer lead to low luminance and external quantum efficiency of perovskite LEDs. We show here the addition of an optimum amount of sodium bromide in the methylammonium lead bromide (MAPbBr3) precursor during a one-step perovskite solution casting process can effectively improve the film coverage, enhance the crystallinity, and passivate ionic defects on the surface of MAPbBr3 crystal grains, resulting in LEDs with a reduced turn-on voltage from 2.8 to 2.3u2009V and an enhanced maximum luminance from 1059 to 6942u2009Cd/m2 when comparing with the pristine perovskite-based device.

Restrained light-soaking and reduced hysteresis in perovskite solar cells employing a helical perylene diimide interfacial layer

An n-type helical molecule perylene diimide (PDI2) has been explored as an efficient interfacial layer between TiO2 and perovskite for the preparation of perovskite solar cells. The extended π-conjugation of PDI2 ensures a high electron conductivity for efficient charge transport, and the oxygen atoms of the carbonyl groups can chelate with uncoordinated Pb2+ to passivate the surface defects of perovskite crystals. It thereby suppresses interfacial recombination, enhances efficiency, and reduces hysteresis and the light-soaking instability. The power conversion efficiency (PCE) of our perovskite solar cells showed negligible dependence on the thickness of the PDI2 interlayer, and the champion device achieved a high PCE of 19.84% and the hysteresis value (ΔPCE) was reduced to 2.34% compared to 6.46% in the perovskite device without the presence of the PDI2 interlayer.

Environmentally durable superhydrophobic surfaces with robust photocatalytic self-cleaning and self-healing properties prepared via versatile film deposition methods

Superhydrophobic (SH) surfaces with self-cleaning photocatalytic properties have become an important research focus in recent years. In this work, we fabricated multifunctional and environmentally durable SH surfaces via a facile one-step reaction of octadecyl isocyanate (ODI) with TiO2 particles. The resulting films possess SH properties, facilitated by a combination of hydrophobic long alkyl chains and the hierarchical crystalline structure. Films can be prepared via spray or blade coating on a variety of hard and soft substrates, and function well when exposed to either air or oil. The coating retains its SH properties for at least 6u202fmonths in ambient conditions, and after organic pollution it can recover its SH properties using UV or sun light illumination. After water impalement, the SH properties can self-heal via the self-assembly of long alkyl chains to their original state within several hours at ambient conditions, or within minutes on a heating stage. The covalent bonds between alkyl chains and TiO2, together with hydrogen bonds between adjacent alkyl chains, greatly increased the surface durability of the SH films. This multifunctional SH coating is a very promising material for commercial and industrial coating applications.

The impacts of PbI2 purity on the morphology and device performance of one-step spray-coated planar heterojunction perovskite solar cells

We have fabricated planar heterojunction perovskite solar cells by one-step ultrasonic spray-coating of the perovskite precursor solution in air. Uniform perovskite films with high surface coverage can be prepared after optimization of the precursor solution and spray-coating parameters. We found that the purity of PbI2, although varying only from 98 to 99.9%, can significantly affect the crystallinity, grain size and boundaries of MAPbI3 films that were fabricated via one-step spray-coating, and ultimately determined the power conversion efficiency (PCE) of perovskite devices. PbI2 with a purity of 98% resulted in a low conversion of precursors to perovskites, whilst a high purity of 99.9% led to perovskites with a high crystallinity, large grain size and narrow grain boundaries. Our p–i–n type, planar heterojunction solar cell ITO/PEDOT:PSS/MAPbI3/PCBM/Ag made from MAI and 99.9% purity PbI2 achieved a maximum PCE of 12.6% without hysteresis, whereas the 98% purity PbI2-based device showed a low PCE of only 4.9% with the presence of hysteresis. However, the impacts of PbI2 purity on the device efficiency can be minimized by changing the deposition method from one-step spray-coating to a two-step spin casting approach.

Improved Efficiency in Fullerene and Non-fullerene Polymer Solar Cells having an Interdigitated Interface with the Electron Transport Layer

We report improved efficiency in fullerene and non-fullerene polymer solar cells utilizing an interdigitated interface between the photoactive layer and the PFN-OX electron transport layer (ETL). This interdigitated interface is formed in situ during the solution casting process of the photoactive layer on the blend films made of electron-transporting PFN-OX and template materials of either semi-conducting 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis((4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene) (ITIC) or insulating polystyrene (PS). Compared to the devices having a planar interface between PFN-OX and the photoactive layer, devices with an interdigitated interface templated by ITIC increased the efficiency of PTB7-Th:PC71BM solar cells from 9.3% to 10.4%, with the device having an interdigitated interface templated by PS exhibiting a PCE of 9.9%. PTB7-Th:ITIC non-fullerene solar cells employing this ITIC-templated interdigitated PFN-OX ETL exhibited an enhanced PCE from 7.4% to 8.3%. Interfacial charge transport studies support that favorable electrical doping of PFN-OX to ITIC as well as charge transfer between PTB7-Th and ITIC contribute to this superior efficiency enhancement in devices employing an ITIC-templated interdigitated PFN-OX ETL. This work provides a new strategy for constructing a novel ETL to prepare high efficiency polymer solar cells.

Halogen-substituted Fullerene Derivatives for Interface Engineering of Perovskite Solar Cells

The interface between perovskites and charge transport layers is crucial for the power conversion efficiency and stability of perovskite solar cells (PSCs). We report for the first time the exploration of three novel fullerene derivatives, N-ethyl-2-arylvinyl-5-methyl fulleropyrrolidine (NAMF) with H, Cl or Br substitutions on the pyrrolidine side-chain (namely NAMF-H, NAMF-Cl and NAMF-Br), via a low cost and one-step reaction from C60, as the interlayer to enhance the efficiency and eliminate hysteresis in planar heterojunction PSCs. The crystallinity of MAPbI3 perovskite cast on these interlayer materials was found to be similar, but the grain size increased and the grain boundaries reduced. All three fullerene derivatives have well-aligned LUMO levels that facilitate electron transport from the perovskite to TiO2, and reduce trap density and charge recombination in PSCs, leading to enhanced device efficiency and reduced hysteresis. Notably, the NAMF-Cl interlayer was found to chlorinate the TiO2 electron transport layer, leading to an enhanced PCE of 19.2% in the reverse scan and 17.7% in the forward scan, which were greater than those of PCBM-based PSC devices. Our work adds a new direction to the design of new fullerene derivatives with favorable physical and electrical properties as interlayer materials to improve the performance of PSCs.