Strong Electron Acceptor of a Fluorine-Containing Group Leads to High Performance of Perovskite Solar Cells

Abstract

Organic−inorganic hybrid perovskites have become one of the most promising thin-film solar cell materials owing to their remarkable photovoltaic properties. However, nonradiative recombination of carriers usually leads to inferior performance of perovskite (PVK) devices. Interface modification is one of the effective ways to improve separation of charges for perovskite solar cells (PSCs). Here, a small organic molecule of tetrafluorophthalonitrile (TFPN) is used to enhance the extraction and transportation of carriers at the PVK/hole transport layer (HTL) interface. The electron-rich C−F group effectively reduces the trap state density in the perovskite through chemical combination with the empty orbital of Pb 2+ or other electron traps on the PVK surface, resulting in enhanced interface contact between the PVK and HTL. Meanwhile, the CN group in TFPN also inactivates the defects caused by Pb 2+ . The Fermi level of the perovskite shifts by 0.15 eV to its valence band due to the strong electron acceptor nature of the F atom, indicating that positive dipoles and p-type doping emerge, which validly suppress the recombination of carriers for the PVK film. Therefore, the optimized PSC shows the highest power conversion efficiency (PCE) of 22.82% compared to 19.40% for the control one. The champion FF reaches up to 81.2% (PCE 21.44%) due to the effectively enhanced carrier separation. In addition, the unencapsulated device shows enhanced stability under air conditions.

Enhanced Bending Resistance and Efficiency of Flexible PSCs Derived from Self‐Healing and Passivation Double Function of a Silane Coupling Agent

“…The much weaker Si-O peak of the modified perovskite film compared to VTMES manifest that VTMES connected with perovskite by forming PbO bonding due to oxydic properties of ionic oxygen atoms. [28,36] In addition, Figure S2 (Supporting Information) shows X-ray photoelectron spectroscopy (XPS) of control and modified perovskite films. Pb 4f peaks shift from 138.20 and 143.10 eV to 138.41 and 143.25 eV (Figure S2b, Supporting Information), and O 1s peak shift from 532.34 to 532.56 eV (Figure S2c, Supporting Information) for control and VTMES-modified films, respectively.…”

“…In addition, with 3 mg mL −1 VTMES modification, the intensity of perovskite (110) and (220) plane is enhanced, and the corresponding PbI 2 peak is obviously restrained, demonstrating that VTMES is of great importance to promote the crystallization of perovskite crystal during the post-treatment process to contribute the conversion from PbI 2 to perovskite phase. [27,28] A small amount of excessive PbI 2 can passivate defects, which is conducive to improving the quality of perovskite films. [24] However, too much quantity of PbI 2 would restrain grain growth of perovskite, thus leading to grain boundary defects and inferior stability.…”

Sulfonyl and Carbonyl Groups in MSTC Effectively Improve the Performance and Stability of Perovskite Solar Cells

“…Meanwhile, the Pb 4 f peak between PbI 2 and MSTC‐PbI 2 is shifted from 138.19 and 143.09 eV to 138.51 and 143.43 eV (Figure 2e), and the O 1 s (532.27–532.52 eV) and the N 1 s (400.18–400.43 eV) (Figure 2f) peak shift between FAI and MSTC‐FAI, further indicating that MSTC could produce chemical connections with PbI 2 and FAI precursor. The shift of Pb 4 f , O 1 s , and N 1 s XPS spectra (Figure S8, Supporting Information) between control, MSTC‐PbI 2 , and MSTC‐FAI perovskite films, respectively, suggests that Pb 2+ could coordinate with O and N atoms in MSTC because the lone pair electrons of O and N would fill the empty orbital of unsaturated Pb 2+ ; [ 17 ] thus, PbI 2 defects have been greatly restrained after the addition of MSTC, in consistent with the XRD results. The coordination bonding of chemical connection between perovskite and MSTC is depicted in Figure 2g.…”

Enhanced Activation Energy Released by Coordination of Bifunctional Lewis Base d-Tryptophan for Highly Efficient and Stable Perovskite Solar Cells

“…In addition, it is found that when the concentration increases to 60 ppm, there is a decrease of perovskite surface morphology and absorption. The reason for this might be that an excess amount of d -tryptophan remains on the surface of perovskite, which decreases the crystallinity of the perovskite film as shown in Figure f …”