In-Situ Electropolymerized Polyamines as Dopant-Free Hole-Transporting Materials for Efficient and Stable Inverted Perovskite Solar Cells

Abstract

Currently, there is an urgent need to develop low-cost hole-transporting materials (HTMs) for inverted perovskite solar cells (PSCs), whose power conversion efficiency (PCE) is still inferior to those with a regular device structure. Herein, we report the successful application of in-situ electropolymerized polyamine films as dopant-free HTMs for efficient and stable inverted PSCs. The oxidative electropolymerization of a readily available star-shaped monomer 1, with a pyrene core and four triphenylamine side arms, affords poly-1 films with networked structures and strong hydrophobicity. A device configuration of ITO/poly-1/(FAPbI3)x(MAPbBr3)(1-x)/PC61BM/BCP/Ag is adopted to yield the best PCE of 16.5%, comparable to that of the device with undoped PTAA as the HTM under the same conditions; however, its steady-state output exhibits distinctly better stability than that of the PTAA-based device. This represents the best performance reported to date of electropolymerized HTMs in PSCs. The dependence of the electropolymer film thickness on the photovoltaic performance reveals an optimal HTM thickness of around 50 nm. Moreover, the PSCs containing poly-1 as the dopant-free HTM exhibit good long-term stability under ambient conditions (91% efficiency is retained after 1000 h) as compared to devices with PTAA. This work offers an avenue for developing cost-effective and stable electropolymerized polyamines as HTMs for high-performance PSCs and other optoelectronic devices.

Improving the Interfacial Contact of Screen-Printed Carbon Electrodes for Perovskite Solar Cells

“…Moreover, the CB layer further increases the lifetime of photogenerated carriers to 4.08 ms. The larger lifetime usually leads to a slower recombination rate and a higher Fermi level, which is consistent to the larger V oc in the J – V curves. , …”

“…The larger lifetime usually leads to a slower recombination rate and a higher Fermi level, which is consistent to the larger V oc in the J−V curves. 28,29 Figure 5 shows the humidity stability of unencapsulated devices with CuSCN/CB/GEs and CuSCN/Au electrodes under 70% humidity at 25 °C. After 1000 h of aging process, the average PCE of devices with CuSCN/Au electrodes decreases to 45% of its initial value, which is mainly attributed to the degradation of perovskite layers because of the gradual color change from dark brown to pale yellow.…”

Dopant-free Hole-transporting Materials for CH3NH3PbI3 Inverted Perovskite Solar Cells with an Approximate Efficiency of 20%

“…Inorganic (e.g., NiO x and CuI), organic polymeric, and small molecular materials have been employed to fabricate highly efficient iPSCs. − Polymeric doped poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) and poly­[bis­(4-phenyl)­(2,4,6-trimethylphenyl)­amine] (PTAA) are the most commonly used materials and require a low-temperature solution process compared with inorganic HTMs. , It is necessary for devices with high PCE (based on HTMs) to exhibit high-hole mobility, appropriate highest occupied molecular orbital (HOMO), and lowest unoccupied molecular orbital (LUMO) to attain (a) efficient hole extraction and electron blocking, and (b) good wetting of the perovskite layer. Considerable efforts have also been expended on iPSCs based on organic small-molecule HTMs, as well as a low-temperature solution process similar to that used in the case of polymeric HTMs, along with their simple preparation process and good process ability, without any interfacial layer or dopants. , For example, A new generation of self-assembled monolayers (SAMs) with molecules based on carbazole bodies with phosphonic acid anchoring groups can replace PTAA without any perovskite post-treatments, additives, dopants or interlayers, and its fabricated p–i–n device prepared by coevaporation achieved a maximum PCE of over 21% .…”

The Non‐Innocent Role of Hole‐Transporting Materials in Perovskite Solar Cells

“…Other remarkable crosslinking approaches reported in the past two years by different groups regard the incorporation of fluorine moieties within a crosslinkable and dopant-free smallmolecule HTM to further boost hydrophobicity of the chargeextracting layer and target defect-passivating interactions with the perovskite surface, [135] the use of electropolymerization to induce in situ formation of polyamine-based dopant-free HTMs for inverted PSCs, [136] and the in situ thermal conversion of solution-processable xanthate precursors into the corresponding insoluble glycol-derivatized poly(1,4-phenylenevinylene) HTMs with different hydrophilicity profiles influencing final device performance. [137] The insertion of an interfacial layer between the perovskite and the HTM or the HTM and the top metal electrode has been shown in other cases to be advantageous for reducing charge recombination in PSCs, [138,139] also through the passivation of surface defects in the semiconductor.…”