Towards Highly Efficient Monolithic Tandem Devices with Perovskite Top Cells
Steve Albrecht a b
a Young Investigator Group Perovskite Tandem Solar Cells, Helmholtz-Center Berlin
b Technical University Berlin, Faculty IV – Electrical Engineering and Computer Science
nanoGe Perovskite Conferences
Proceedings of nanoGe International Conference on Perovskite Solar Cells, Photonics and Optoelectronics (NIPHO19)
International Conference on Perovskite Thin Film Photovoltaics
Jerusalem, Israel, 2019 February 24th - 27th
Organizers: Lioz Etgar and Kai Zhu
Invited Speaker, Steve Albrecht, presentation 055
Publication date: 21st November 2018

Integrating inorganic–organic perovskite top cells with crystalline silicon or CIGS bottom cells into monolithic tandem devices has recently attracted increased attention due to the high efficiency potential of these cell architectures. To further increase the tandem device performance to a level well above the best single junctions, optical and electrical optimizations as well as a detailed device understanding of this advanced tandem architecture need to be developed. Here we present our recent results on monolithic tandem combinations of perovskite with crystalline silicon and CIGS, as well as tandem relevant aspects of perovskite single junction solar cells. By selecting a front contact layer stack with less parasitic absorption and utilizing the p-i-n perovskite top cell polarity, a certified conversion efficiency of 25.0% for a monolithic perovskite/silicon tandem solar cells was enabled. Further fine-tuning of the stack optics as well as contact layers improved the efficiency to 26.0% and we present how highly efficient tandem solar cells behave under current-mismatch conditions. Additionally, the introduction of light trapping foils with textured surfaces is presented together with the influence on texture position on lab performance and outdoor energy yield.[1] The monolithic combination of perovskite and CIGS was highly challenging up to now as the CIGS surface is rather rough. By implementing a conformal hole transport layer, an efficient monolithic perovskite/CIGS tandem was realised. Absolute photoluminescence of the perovskite and CIGS sub-cells gives insights into the contributions to the tandem open-circuit voltage (Voc). To further improve the tandem efficiency, the Voc of perovskite top cells needs to be enhanced via reduction of non-radiative recombination at the interface between perovskite and the charge selective layers. This can either be done via proper interlayers[2] or via fine-tuned charge selective contacts. Recently we have shown that self-assembled monolayers (SAM) could be implemented as appropriate hole selective contacts.[3] The implementation of new SAM molecules enabled further reduction of non-radiative recombination losses with Voc’s up to 1.19 V and efficiency of 21.2% for perovskite single junctions with band gaps of 1.63 eV and 1.55 eV, respectively.  

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