Advanced Functional Materials and Devices (AFMD) Group

Abstract:

Metal-halide perovskite light-absorbers have risen to the forefront of photovoltaics research offering the potential to combine low-cost fabrication with high power-conversion efficiency. Much of the development has been driven by empirical optimisation strategies to fully exploit the favourable electronic properties of the absorber layer. To build on this progress, a full understanding of the device operation requires a thorough optical analysis of the device stack, providing a platform for maximising the power conversion efficiency through a precise determination of parasitic losses caused by coherence and absorption in the non-photoactive layers. Here we use an optical model based on the transfer-matrix formalism for analysis of perovskite-based planar heterojunction solar cells using experimentally determined complex refractive index data. We compare the modelled properties to experimentally determined data, and obtain good agreement, revealing that the internal quantum efficiency in the solar cells approaches 100%. The modelled and experimental dependence of the photocurrent on incidence angle exhibits only a weak variation, with very low reflectivity losses at all angles, highlighting the potential for useful power generation over a full daylight cycle.

Abstract:

© 2014 Elsevier Ltd. All rights reserved.The adaptation of interfacial layers to the stacked architecture of organic solar cells represents a very useful strategy for improved device operation. In this context, heteroacenic structures such as carbazolocarbazoles have been doped and evaluated as hole transporting materials in small molecule solar cell with either inverted or conventional architecture. S-kinks in the IV-curve detected for the inverted solar cells could be remarkably corrected by reversing the deposition sequence, highlighting the importance of buffer layer adjustment. Some of the studied carbazolocarbazoles proved to be a suitable molecule to be used as hole transporting materials.