Hole transport layers (HTLs) are of fundamental importance in perovskite solar cells (PSCs), as they must ensure an efficient and selective hole extraction, and ohmic charge transfer to the corresponding electrodes. In p-in solar cells, the ITO/HTL is usually not ohmic, and an additional interlayer such as MoO 3 is usually placed in between the two materials by vacuum sublimation. In this work, we evaluated the properties of the MoO 3 /TaTm (TaTm is the HTL N4,N4,N4 ′′ ,N4 ′′-tetra([1,1 ′-biphenyl]-4-yl)-[1,1 ′ :4 ′ ,1 ′′-terphenyl]-4,4 ′′-diamine) hole extraction interface by selectively annealing either MoO 3 (prior to the deposition of TaTm) or the bilayer MoO 3 /TaTm (without pre-treatment on the MoO 3), at temperature ranging from 60 to 200 • C. We then used these p-contacts for the fabrication of a large batch of fully vacuum deposited PSCs, using methylammonium lead iodide as the active layer. We show that annealing the MoO 3 /TaTm bilayers at high temperature is crucial to obtain high rectification with low non-radiative recombination, due to an increase of the electrode work function and the formation of an ohmic interface with TaTm.
Nanocrystals surface chemistry engineering offers a direct approach to tune charge carrier dynamics in nanocrystals-based photodetectors. For this purpose, we have investigated the effects of altering the surface chemistry of thin films of CsPbBr3 perovskite nanocrystals produced by the doctor blading technique, via solid state ligand-exchange using 3-mercaptopropionic acid (MPA). The electrical and electro-optical properties of photovoltaic and photoconductor devices were improved after the MPA ligand exchange, mainly because of a mobility increase up to 5 × 10−3 cm 2 / Vs . The same technology was developed to build a tandem photovoltaic device based on a bilayer of PbS quantum dots (QDs) and CsPbBr3 perovskite nanocrystals. Here, the ligand exchange was successfully carried out in a single step after the deposition of these two layers. The photodetector device showed responsivities around 40 and 20 mA/W at visible and near infrared wavelengths, respectively. This strategy can be of interest for future visible-NIR cameras, optical sensors, or receivers in photonic devices for future Internet-of-Things technology.
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