Abstract
We present some advanced characterization techniques developed to investigate on the opto-electronic properties of thin film semiconductors and apply them to perovskite layers. These techniques are the steady state photocarrier grating (SSPG) and the Fourier transform photocurrent spectroscopy (FTPS). The SSPG was developed to study the ambipolar diffusion length of carriers and the FTPS was imagined to measure the variations of the below gap absorption coefficient with the light energy, giving information on the defect densities of the gap responsible for this absorption. The potentialities of these techniques are first detailed and then exemplified by their application to thin film perovskites. To study their stability, these films were exposed to different environments, air or vacuum, and in their as-deposited state or after light-soaking with heavy light. We find that the diffusion length and density of states are quite stable, even after light-soaking, and suggest that the degradation of devices exposed to 1 sun mainly comes from the evolution of the contacts instead of the perovkite itself.
Highlights
Since the first demonstration that perovskites could be used as absorbers in solar energy conversion devices [1], these latters have shown in few years the fastest increase of conversion efficiency ever recorded
We find that the diffusion length and density of states are quite stable, even after light-soaking, and suggest that the degradation of devices exposed to 1 sun mainly comes from the evolution of the contacts instead of the perovkite itself
As far as the PVK thin films we have studied are concerned, the experimental results presented in Section 4 can be summarized as follows: – air is not systematically detrimental to the transport properties of the PVK films since we have observed a decrease of the transport parameters, Lamb and sph, when the samples were put under vacuum
Summary
Since the first demonstration that perovskites could be used as absorbers in solar energy conversion devices [1], these latters have shown in few years the fastest increase of conversion efficiency ever recorded. Some of the origins of these instabilities are assumed to be linked to (i) the degradation of the perovskite (PVK) absorber by an air component (oxygen, moisture, etc.) and (ii) the influence of heavy light under which all solar devices are supposed to work In this communication we investigate some of the optoelectronic properties, and their evolution under different stresses, of perovskite thin films by means of several experiments, which, to our knowledge, were not systematically applied to this material. To study the transport properties of these samples we have used the Steady State Photo Conductivity (SSPC) technique and the Steady States Photocarrier Grating (SSPG) technique [2] This last technique has been largely improved to automatically perform measurements within a few minutes [3] to follow the fast evolution of the ambipolar diffusion length when experimental conditions, e.g. samples in air or under vacuum, are modified.
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