Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
DOI: https://doi.org/10.29363/nanoge.hopv.2022.121
Publication date: 20th April 2022
Since their introduction in 2017, the efficiency of lead-free halide perovskite solar cells based on Cs2AgBiBr6 has not exceeded 3%, although theoretical limits predict maximum efficiencies of up to 7.9%.[1] The limiting bottlenecks are attributed to a low electron diffusion length, self-trapping events and poor selectivity of the contacts, leading to large non-radiative VOC losses.[2] Here, we introduce the strategy of creating a 2D/3D perovskite double layer, for double perovskite solar cells to overcome some of the bottlenecks (Figure 1 left). The resulting solar cells show an increased efficiency of up to 2.5% for the champion cells and 2.03% on average, marking an improvement by 10% compared to the 3D reference on mesoporous TiO2. We compared the organic spacer cations butylammonium (BA), phenethylammonium (PEA) and 4-fluorophenethylammonium (4FPEA) and systematically investigated the reasons for improvement on a model system with (PEA)4AgBiBr8/Cs2AgBiBr6 as the 2D/3D double perovskite layer. The improvement is mainly due to a VOC increase by up to 70 mV on average, yielding a maximum VOC of 1.18 V using different concentrations of PEA precursor spin-coating solutions. These voltages are among the highest reported VOC values for Cs2AgBiBr6 solar cells. We attribute this effect to a change in recombination behavior within the full device and a better selectivity at the interface toward the hole transporting material (HTM). This explanation is supported by the voltage-dependent external quantum efficiency, and by results from photoelectron spectroscopy, revealing a better energy level alignment and thus a better hole-extraction and improved electron blocking at the HTM interface (Figure 1 right).[3]
The authors acknowledge funding from the German Federal Ministry of Education and Research (BMBF) under the agreement number 03SF0516B, the Bavarian Ministry of the Environment and Consumer Protection, the Bavarian Network “Solar Technologies Go Hybrid”, the German Science Foundation (DFG) focus program SPP 2196 and the DFG Excellence Cluster e-conversion (EXC 2089/1-390776260). The authors thank Dr. Steffen Schmidt for performing the SEM measurements.
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International Conference on Hybrid and Organic Photovoltaics (HOPV) is celebrated yearly in May. The main topics are the development, function and modeling of materials and devices for hybrid and organic solar cells. The field is now dominated by perovskite solar cells but also other hybrid technologies, as organic solar cells, quantum dot solar cells, and dye-sensitized solar cells and their integration into devices for photoelectrochemical solar fuel production.
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