device performance of 15.7% is currently the highest performance achieved for perovskite solar cells, pointing towards planar heterojunction devices as a promising device architecture for further technological improvements.The short circuit currents demonstrated for the devices prepared by Liu and co-workers of 20.4 mA cm −2 , [ 7 ] while high, are still short of the maximum current of over 22 mA cm −2 reasonably achievable, taking into account other light capture losses for this material. [ 3a ] A crucial limitation in this respect is the low diffusion length of around ≈100 nm of the photoexcited species in the MAPbI 3 perovskite. [ 8 ] This parameter can be greatly extended to over 1 µm with the inclusion of chloride in the precursor solution. [ 8a , 9 ] Furthermore, it has been recently shown that the inclusion of chloride is benefi cial for charge transport in the photoactive layer. [ 10 ] It is expected that the addition of chloride results in improved short circuit currents and thus overall photovoltaic performance. It is worth noting here that for devices incorporating mesoporous TiO 2 photoanodes, the neat tri-iodide perovskite functions effi ciently without the need for the extended diffusion length of the photoexcited species. [ 11 ] This is a result of the interpenetrated nature of the collection photoanode, which exhibits pore sizes at the order of tens of nanometers, and in effect reduces the distance electrons must travel to this magnitude before being collected. In the case of planar heterojunctions, electrons must travel the entire thickness of the fi lm, which can sometimes exceed hundreds of nanometers and thus extended diffusion lengths are a requirement for effi cient operation.Here we present planar, fully solution-processed heterojunction solar cells based on the solution deposition-conversion technique. We highlight that chloride is critical in MA lead halide perovskites via a controlled addition of methylammonium chloride (MACl) to the MAI immersion solution. The resulting devices exhibited power conversion effi ciencies approaching 15%, and more importantly, showed short circuit currents of over 22 mA cm −2 , representing a gain of over 10% over stateof-the-art devices. [ 7 ] The parameter most infl uenced by the presence of chloride is the photoluminescence lifetime of the photoexcited species in the device, which reaches values exceeding 300 ns, matching previously reported results for the solution processed mixed halide perovskite fi lms. [ 8a ] Additionally, a reduction of series resistance from 14 to 7 Ω cm 2 was observed.The solar cells developed in this work are composed of a TiO 2 /perovskite/Spiro-MeOTAD planar heterojunction, deposited on a fl uorine-doped tin oxide (FTO) electrode and capped with a gold electrode ( Figure 1 ). The perovskite deposition was performed in two steps: fi rstly, an ≈200 nm PbI 2 fi lm The alkylammonium metal trihalide perovskite absorbers fi rst used in working photovoltaic devices were based on liquid electrolyte sensitized solar cells. Introduc...

Spray coating, a simple and low‐cost technique for large‐scale film deposition, is employed to fabricate mesoporous titania films, which are electron‐transporting layers in all‐solid‐state dye‐sensitized solar cells (DSSCs). To optimize solar cell performance, presynthesized crystalline titania nanoparticles are introduced into the mesoporous titania films. The composite film morphology is examined with scanning electron microscopy, grazing incidence small‐angle X‐ray scattering, and nitrogen adsorption–desorption isotherms. The crystal phase and crystallite sizes are verified by X‐ray diffraction measurements. The photovoltaic performance of all‐solid‐state DSSCs is investigated. The findings reveal that an optimal active layer of the all‐solid‐state DSSC is obtained by including 50 wt% titania nanoparticles, showing a foam‐like morphology with an average pore size of 20 nm, featuring an anatase phase, and presenting a surface area of 225.2 m2 g−1. The optimized morphology obtained by adding 50 wt% presynthesized crystalline titania nanoparticles yields, correspondingly, the best solar cell efficiency of 2.7 ± 0.1%.

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Although macroporous titania scaffolds are used for many different applications, not much is known about the importance of the synthesis strategy on the resulting materials' properties. We present a comparative study on the influence of different colloidal titania precursors for direct co-deposition with poly(methyl methacrylate) (PMMA) beads on the properties of the resulting macroporous scaffolds after calcination.The colloidal titania precursors for the film assembly differ in their size and initial crystallinity, ranging from amorphous sol-gel clusters to already crystalline pre-formed particles of 4 nm, 6 nm and 20 nm in size, as well as a combination of sol-gel and nanoparticle precursors in the so-called 'Brick and Mortar' approach. The type of the precursor greatly influences the morphology, texture and the specific crystallinity parameters of the macroporous titania scaffolds after calcination such as the size of the crystalline domains, packing density of the crystallites in the macroporous walls and interconnectivity between the crystals. Moreover, the texture and the crystallinity of the films can be tuned by postsynthesis processing of the films such as calcination at different temperatures, which can be also preceded by a hydrothermal treatment. The ability to adjust the porosity, the total surface area and the crystallinity parameters of the crystalline macroporous films by selecting suitable precursors and by applying different post-synthetic treatments provides useful tools to optimize the film properties for different applications.