Blocking pinholes with selective molecular layers: a key to improved efficiency and reproducibility in opaque and semi-transparent perovskite solar cells

Clara Beck^a, Maximilian Hörantner^a, Pabitra Nayak^a, Giles Eperon^a, Henry Snaith^a

^aUniversity of Oxford, Clarendon Laboratory, Parks Road, United Kingdom

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Poster, Maximilian Hörantner, 218
Publication date: 5th February 2015

Perovskite solar cells have quickly disrupted the photovoltaic research field due to the fast rate of improving efficiencies and their cost-effective fabrication processes. With the present rate of progress, this type of cells can show the best power conversion efficiencies among the thin-film poly-crystalline technologies in the near future. With a potential to be manufactured as low-cost large area cells (or large modules) this technology can change the paradigm in solar cell development. However, often the perovskite thin films suffer from pinholes that allow direct connection between the hole transporting layer and the electron transporting oxide layers which in turn provides shunt pathways. Lower shunt resistance is manifested in lower open circuit voltage (Voc) and fill factor (FF) of a cell. The prevalence of pinholes is a major bottleneck to produce efficient large area cells (or modules as it also reduces the reproducibility of cells). For the above reasons, the yield of high performing planar-heterojunction devices is low and the reproducibility varies significantly as compared to those incorporating mesoporous scaffolds. Moreover, the issue is more severe in case of neutral colour semi-transparent cells where large uncovered oxide layers are needed. In this presentation we will present a simple yet effective wet chemical based technique to block these shunting paths via deposition of an insulating molecular layer (after the fabrication of perovskite films) that selectively binds to the uncovered oxide surface and therefore does not prevent charge extraction from the perovskite. We show that this easily employable method leads to notably improved Voc’s up to 30% enhancement, without impacting the photocurrent. Particularly cells with small active layer coverage improved remarkably, which enhances semi-transparent perovskite device efficiency. Furthermore, we analyze the electronic characteristics of the devices and show evidence for reduced recombination via impedance spectroscopy. Generally this simple shunt blocking technique can help with the reproducible fabrication of perovskite solar cells on large areas.

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