• Energy Research

Thin (approximately 10 nm) oxide buffer layers grown over lead-halide perovskite device stacks are critical for protecting the perovskite against mechanical and environmental damage. However, the limited perovskite stability restricts the processing methods and temperatures (<=110 C) that can be used to deposit the oxide overlayers, with the latter limiting the electronic properties of the oxides achievable. In this work, we demonstrate an alternative to existing methods that can grow pinhole-free TiOx (x = 2.00+/-0.05) films with the requisite thickness in <1 min without vacuum. This technique is atmospheric pressure chemical vapor deposition (AP-CVD). The rapid but soft deposition enables growth temperatures of >=180 ��C to be used to coat the perovskite. This is >=70 ��C higher than achievable by current methods and results in more conductive TiOx films, boosting solar cell efficiencies by >2%. Likewise, when AP-CVD SnOx (x ~ 2) is grown on perovskites, there is also minimal damage to the perovskite beneath. The SnOx layer is pinhole-free and conformal, which reduces shunting in devices, and increases steady-state efficiencies from 16.5% (no SnOx) to 19.4% (60 nm SnOx), with fill factors reaching 84%. This work shows AP-CVD to be a versatile technique for growing oxides on thermally-sensitive materials. R.D.R and R.A.J contributed equally. 23 pages. 6 figures

AbstractA thin ZnO (<200nm) film grown by Atmospheric Atomic Layer Deposition (AALD) in a matter of minutes was studied as a hole-blocking layer in poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61-buyric acid methyl ester (P3HT:PCBM) based inverted solar cells. These AALD ZnO layers were compact, had a high electron mobility of 3.4+0.1cm2/Vs, had up to 100% transmittance to visible light, and a good wettability for the blend. Despite the very rapid, open atmosphere growth method, the cell performance was comparable with some of the best inverted bulk heterojunction P3HT:PCBM cells in the literature. The performance was also maintained after 200 days of storage in air in the dark.

Abstract The implementation of nano-engineered composite oxides opens up the way towards the development of a novel class of superior energy materials. Vertically aligned nanocomposites are characterized by a coherent, dense array of vertical interfaces, which allows for the extension of local effects to the whole volume of the material. Here, we use such a unique architecture to fabricate highly electrochemically active nanocomposites of lanthanum strontium manganite and doped ceria with unprecedented stability and straight applicability as functional layers in solid state energy devices. Direct evidence of synergistic local effects for enhancing the electrochemical performance, stemming from the highly ordered phase alternation, is given here for the first time using atom-probe tomography combined with oxygen isotopic exchange. Interface-induced cationic substitution, enabling lattice stabilization, is presented as the origin of the observed long-term stability. These findings reveal a novel route for materials nano-engineering based on the coexistence between local disorder and long-range arrangement.

Abstract We investigate the potential of Nd doped SrTiO3 films for the photon downshifting of ultraviolet photons to infrared ones. We first studied the structural properties of such newly developed layers grown by pulsed laser deposition (PLD). We also show that these layers allow the conversion of photons from 250–350 nm excitation to around 900 nm. We implemented the optimized Nd:SrTiO3 thin films on a conventional silicon solar cell and we show that the internal quantum efficiency is increased at around 350 nm which validates the concept of downshifting applied to solar cells. Future work will be to determine if downconversion takes place in this system.

Heterojunction Cu2O solar cells are an important class of Earth-abundant photovoltaics that can be synthesized by a variety of techniques, including electrochemical deposition (ECD) and thermal oxidation (TO). The latter gives the most efficient solar cells of up to 8.1% reported in the literature, but is limited by low external quantum efficiencies (EQE) in the long wavelength range (490–600 nm). By contrast, ECD Cu2O gives higher short wavelength EQEs of up to 90%. We elucidate the cause of this difference by characterizing and comparing ECD and TO films using impedance spectroscopy and fitting with a lumped circuit model to determine the trap density, followed by simulations. The data indicates that TO Cu2O has a higher density of interface defects, located approximately 0.5 eV above the valence band maximum (NV), and lower bulk defect density thus explaining the lower short wavelength EQEs and higher long wavelength EQEs. This work shows that a route to further efficiency increases of TO Cu2O is to reduce the density of interface defect states.