Our recent work (1) has shown that polymer wrapped carbon nanotubes can be used to transform the properties of the hole transporting layer in a number of different perovskite based solar cell configurations. This presentation will report on two examples where the CNT hole transporter produces enhanced device performance, firstly for tin oxide/perovskite alloy/CNT devices and secondly in PbS colloidal quantum dots (CQD) where improved charge extraction by the CNT is particularly important.

Halide perovskite solar cells remain to generate a lot of interest and enthusiasm among researchers, largely due to the prospect of readily transitioning from a purely lab based technology to real-world scales. This expectation is largely based on the rapid increase in efficiency over the past few years to values above 22%. An essential component of this device architecture are the two charge selective contacts. The n-type contact in the majority of all devices is TiO₂, either as a thin compact layer, or a mesostructured configuration, but recently, SnO₂ has moved into the spotlight as n-type contact with recent studies reporting excellent steady-state performances.

The p-type contact on the other side of the absorber has been investigated even more intensively. The best-performing devices still use the “original” hole-transport material, spiro-OMeTAD, which provided the crucial breakthrough for the perovskite solar cell in 2012, but which suffers from the fact that it is not sufficiently conductive for efficient charge-transport, and requires extrinsic doping, typically with Li-TFSI, which has been shown to detrimentally impact the device stability. This presentation will demonstrate that for FA_0.83MA_0.117Pb(I_0.87Br_0.17)₃ based solar cells we can achieve steady-state efficiencies of up to 18.8%, by using polymer-wrapped single-walled carbon nanotubes (SWNTs) as an inert conductive element in undoped spiro-OMeTAD, exceeding the performance of their fully doped counterparts.

In a completely different example we can use the same polymer wrapped SWNTs as a hole collection electrode for PbS based CQD photodetectors which are capable of operating over a spectral range extending beyond one micron. We find that the use of a polymer wrapped CQD combined with PMMA filler more than doubles the current collection in such devices and enables efficiencies of over 7%. In addition the SWNT layer produces a substantial improvement in long term device stability in normal ambient conditions.

(1) Habisreutinger, S. N.; Leijtens, T.; Eperon, G. E.; Stranks, S. D.; Nicholas, R. J.; Snaith, H. J. Nano Lett. 2014, 14, 5561–5568.