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Carrier Extraction from Perovskite to Polymeric Charge Transport Layers Probed by Ultrafast Transient Absorption Spectroscopy.

Research paper by Esma E Ugur, Jafar Iqbal JI Khan, Erkan E Aydin, Mingcong M Wang, Mindaugas M Kirkus, Marios M Neophytou, Iain I McCulloch, Stefaan S De Wolf, Frédéric F Laquai

Indexed on: 21 Mar '21Published on: 22 Oct '19Published in: Journal of Physical Chemistry Letters



Abstract

The efficiency of state-of-the-art perovskite solar cells is limited by carrier recombination at defects and interfaces. Thus, understanding these losses and how to reduce them is the way forward towards the Shockley-Queisser limit. Here, we demonstrate that ultrafast transient absorption spectroscopy can directly probe hole extraction, and recombination dynamics at perovskite/hole transport layers (HTLs) interfaces. To illustrate this, we employed PDPP-3T as HTL, since its ground state absorption is at lower energy than the perovskite's photobleach, enabling direct monitoring of interfacial hole extraction and recombination. Moreover, by fitting the carrier dynamics using diffusion model, we determined the carrier mobility. Then, by varying the perovskite thickness, we distinguished between carrier diffusion and carrier extraction at the interface. Lastly, we prepared device-like structures, TiO/perovskite/PDPP-3T stacks, and observed reduced carrier recombination in the perovskite. From PDPP-3T carrier dynamics, we deduced that hole extraction is one-order faster than recombination of holes at the interface.