Up to 1.94 V Open Circuit Voltage in Highly Efficient Perovskite/Silicon Tandem Solar Cells Using Polymeric Interlayers in the Top Contact
Bor Li a, Marlene Härtel a b, Amran Al-Ashouri a, Eike Köhnen a, Kari Sveinbjörnsson a, Artem Musiienko a, Philipp Wagner a, Bernd Stannowski a, Lars Korte a, Steve Albrecht a b
a Helmholtz-Zentrum Berlin für Materialien und Energie, Division Solar Energy, 12489 Berlin, Germany
b Technische Universität Berlin - Fakultät Elektrotechnik und Informatik, 10587 Berlin, Germany
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Poster, Bor Li, 227
Publication date: 20th April 2022

Metal halide perovskite solar cells have been improving significantly over the past decade. Their versatile material properties allow the combination with silicon solar cells in monolithic tandem configurations achieving power conversion efficiencies (PCE) above 29 %.[1] Semitransparent top contact layers are a key element for high efficiency perovskite based tandem solar cells.[2] In addition, these top contact layers, namely tin oxide (SnO2) deposited by atomic-layer deposited (ALD) and indium zinc oxide (IZO) deposited by RF-magnetron sputtering, protect the perovskite solar cells against decomposition reactions in humid air and at high temperature, thus improving long term stability. However, the deposition process of top contact layers often induces fill factor (FF) and open circuit voltage (VOC) losses due to perovskite degradation and/or process related defect generation.[3]

In this work, VOC differences between tandem-relevant cells processed with different electron-selective contacts are quantified. We show how VOC losses can be mitigated by using an ultrathin polymer interlayer between the perovskite absorber and the n-type top contact. The perovskite can be protected by introducing polyethylenimine ethoxylated (PEIE), a polymeric interlayer, which reduces degradation and non-radiative recombination losses. This is shown by an increased steady-state photoluminescence quantum yield and improvements in VOC. Additionally, an enhanced nucleation growth of SnO2 on PEIE[4] allows for a thinner and denser SnO2 film. Combined with a thinner C60 layer due to the protective property of PEIE, an overall optical improvement of the top cell transmission could be achieved. Interestingly, PEIE as interlayer between perovskite and C60 can also reduce recombination losses and improve electron extraction as analysed by transient surface photovoltage. These modifications overcome the top contact limitation, increase the overall performance, and push perovskite/silicon tandem solar cells one step closer towards surpassing 30% PCE.

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