Snaith group

Abstract:

Solution-processed metal halide perovskite semiconductors, such as CH3NH3PbI3, have exhibited remarkable performance in solar cells, despite having non-negligible density of defect states. A likely candidate is halide vacancies within the perovskite crystals, or the presence of metallic lead, both generated due to the imbalanced I/Pb stoichiometry which could evolve during crystallization. Herein, we show that the addition of hypophosphorous acid (HPA) in the precursor solution can significantly improve the film quality, both electronically and topologically, and enhance the photoluminescence intensity, which leads to more efficient and reproducible photovoltaic devices. We demonstrate that the HPA can reduce the oxidized I2 back into I−, and our results indicate that this facilitates an improved stoichiometry in the perovskite crystal and a reduced density of metallic lead.

Abstract:

Photovoltachromic devices combine photovoltaic and electrochromic behaviours to enable adjustable transparency glazing, where the photovoltaic component supplies the power to drive the coloration. Such stand-alone, self-powered devices are of commercial interest for integration into windows and surfaces of buildings and vehicles. Here, we report for the first time a perovskite-based photovoltachromic device with self-adaptive transparency. This multifunctional device is capable of producing electrical power by solar energy conversion as well as undergoing a chromic transition from neutral-color semi-transparent to dark blue-tinted when irradiated with solar light, without any additional external bias. The combination of semi-transparent perovskite photovoltaic and solid-state electrochromic cells enables fully solid-state photovoltachromic devices with 26% (or 16%) average visible transmittance and 3.7% (or 5.5%) maximum light power conversion efficiency. Upon activating the self-tinting, the average visible transmittance drops to 8.4% (or 5.5%). These results represent a significant step towards the commercialization of photovoltachromic building envelopes.

Abstract:

Two diacetylide-triphenylamine hole-transport materials (HTM) with varying redox potential have been applied in planar junction TiO2-[CH3NH3]PbI3-xClx solar cells leading to high power-conversion efficiencies up to 8.8%. More positive oxidation potential of the HTM gives higher VOC and lower JSC illustrating the role of matching energy levels, however both HTMs gave efficient cells despite a difference of 0.44 V in their redox potentials.

Abstract:

Herein we describe both theoretically and experimentally the optical response of solution-processed organic-inorganic halide perovskite solar cells based on mesostructured scaffolds. We develop a rigorous theoretical model using a method based on the propagation of waves in layered media, which allows visualizing the way in which light is spatially distributed across the device and serves to quantify the fraction of light absorbed by each medium comprising the cell. The discrimination between productive and parasitic absorption yields an accurate determination of the internal quantum efficiency. State-of-the-art devices integrating mesoporous scaffolds infiltrated with perovskite are manufactured and characterized to support the calculations. This combined experimental and theoretical analysis provides a rational understanding of the optical behavior of perovskite cells and can be beneficial for the judicious design of devices with improved performance. Notably, our model justifies the presence of a solid perovskite capping layer in all of the highest efficiency perovskite solar cells based on thinner mesoporous scaffolds.