How to Boost the Power Conversion Efficiency of Carbon-based Perovskite Solar Cells
Dmitry Bogachuk a b, Lukas Wagner a b, Andreas Hinsch b
a University of Freiburg, Department of Sustainable Systems Engineering (INATECH), Freiburg, 79110, Germany.
b Fraunhofer-Institut für Solare Energiesysteme (FhG ISE), Heidenhofstrasse 2, 79110 Freiburg, Germany
nanoGe Perovskite Conferences
Proceedings of International online conference on Hybrid materials and optoelectronic devices (HYBRIDOE)
Online, Spain, 2020 December 15th - 17th
Organizers: Xueqing Xu, Baomin Xu, Hin-Lap (Angus) Yip and Xinhua Zhong
Oral, Dmitry Bogachuk, presentation 013
DOI: https://doi.org/10.29363/nanoge.hybridoe.2020.013
Publication date: 4th December 2020

Over the years carbon-based counter electrodes have attracted tremendous attention in the perovskite community due to their clear advantages of being a more cost-effective, stable, up-scalable and sustainable alternative to the conventional noble-metal-based electrodes. However, the power conversion efficiencies (PCEs) of cells with such carbon-based electrodes still lags behind the ones with metallic contacts, limiting the commercial attractiveness of such photovoltaic devices. Here we outline the current challenges of reducing surface recombination and ways to improve the charge transfer from the photoabsorber to the electrode. Recently we have conducted a detailed study on the non-radiative charge recombination pathways in the triple-layer (m-TiO2/ZrO2/Carbon) mesoscopic carbon-based perovskite solar cells (C-PSCs), revealing that the surface-defect-induced recombination pathways at the m-TiO2/perovskite and perovskite/Carbon strongly reduce the open-circuit voltage of C-PSCs [1] (although cells with the exceptionally high Voc of 1V for CH3NH3PbI3 perovskite were shown by our group earlier).[2] The non-radiative recombination loss can be minimized by reducing the surface area (i.e. recombination sites) of m-TiO2, but the perovskite/Carbon interface still presents a fundamental challenge that needs to be solved in order to achieve high PCEs. An efficient band-alignment and hole-extracting ability can be obtained by introducing a hole-selective layer between the photoabsorber and the electrode. However, the high-temperature treatment, needed for sintering the carbon-based electrodes leaves a very short list of available inorganic hole-selective layers (such as NiOx), most of which still do not possess as favorable properties as the conventional organic hole-selective layers such as doped spiro-OMeTAD or polymer-based ones, such as PTAA or PolyTBD. Low-temperature carbon-based electrodes (requiring curing temperatures compatible with the layers underneath) provide an appealing opportunity to integrate efficient hole-transport materials between the carbon-based electrode and perovskite, in order to enhance the valence band alignment, reduce the interfacial resistance and surface defects. [3] Over the years the PCEs of mesoscopic cells with high-temperature cured electrodes never went above 17% with the highest certified record efficiency of 15.5% (recently obtained by our group), whereas the current PCE record of C-PSCs with low-temperature cured electrodes is 19.2% [4] and a certified PCE of 17.8%. [5] The key advantages of the latter type of C-PSCs are: the wider range of charge-selective layers, more favorable crystallization kinetics, rapid manufacturing process and compatibility with flexible substrates. In summary we propose effective strategies to improve the charge-selectivity, electrode's conductivity and interface between the carbon-based electrodes and the layers underneath for reaching record device efficiencies. [3]

This work has been partially funded within the projects PROPER financed from the German Ministry of Education and Research under funding number 01DR19007 and UNIQUE supported under umbrella of SOLAR-ERA.NET_cofund by ANR, PtJ, MIUR, MINECO-AEI and SWEA, within the EU's HORIZON 2020 Research and Innovation Program (cofund ERA-NET Action No. 691664). D. B. and L. W. acknowledge the scholarship support of the German Federal Environmental Foundation (DBU).

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