Tri‐Brominated Perovskite Film Management and Multiple‐Ionic Defect Passivation for Highly Efficient and Stable Solar Cells

Abstract

High‐quality perovskite films with low imperfections, high hole mobility, and matching energy levels play a crucial role in enhancing performance of perovskite solar cells (PSCs) without hole‐transporting materials (HTMs). Herein, it is demonstrated that the incorporation of a stable tetra‐bisphenol A (TBBPA) with diphenyl ring, polybromides, and hydroxyl groups additive into a perovskite film can simultaneously manipulate the crystal growth and passivate the defects through coordination interaction between the functional group (OH, Br) and the unsaturated halogen and metal ions (Br−, Cs+, and Pb2+), resulting in a reduced grain boundary as well as imperfection and increased hole mobility of the CsPbBr3 perovskite film. In addition, the valence band of a perovskite film with TBBPA additive is shifted upward to approach the work function of the carbon electrode, thereby improving the energy level alignment. Consequently, a significantly boosted charge extraction and reduced charge recombination of the carbon‐based HTM‐free CsPbBr3 PSCs is obtained after incorporating the TBBPA additive, yielding a maximum power conversion efficiency of up to 9.82% of the optimized device. Furthermore, the champion PSC without encapsulation displays a remarkable thermal and moisture stability after being kept in ambient air for 720 h at 85 °C and 85% relative humidity, respectively.

Enhanced Flexibility and Stability of Emissive Layer Enable High‐Performance Flexible Light‐Emitting Diodes by Cross‐Linking of Biomass Material

“…[19] The abundant hydroxyl groups and hydrophobic ether groups in EC are beneficial to passivate surface defects of perovskites and improve their stability. [11,20] CsI (aq) + PbI 2 , resulting in a size decrease and thus blue-shifted PL. [21] In comparation, the EC-treated CsPbI 3 NCs showed stable PL due to the formation of hydrophobic layer by EC treatment, inhibiting the occurrence of the decomposition reaction.…”

“…In addition, Figure 1g–i shows that the peaks from O 1s, Pb 4f, and I 3d are all shifted to higher binding energies in the EC‐treated NCs compared with the pristine NCs, indicating the chemical interaction between O atoms of EC and the undercoordinated Pb 2+ on the perovskite surface, and the formation of hydrogen bonds between OH and I – within the octahedral framework [PbI 6 ] 4– . [ 11 ] However, the peaks from Cs 3d do not shift (Figure S3b, Supporting Information), implying that there is no interaction between EC and Cs + . Taking into account the above results, we deduce that EC acts as an efficient crystal cross‐linker in the perovskite structures through synergistic effect of both hydrogen bonds and coordination bonds, thus passivates the surface defects of perovskite.…”

“…[ 19 ] The abundant hydroxyl groups and hydrophobic ether groups in EC are beneficial to passivate surface defects of perovskites and improve their stability. [ 11,20 ] Figure a,b shows the PL spectra stability of pristine‐ and EC‐treated CsPbI 3 NCs. The PL spectra of the pristine CsPbI 3 NC solution suffers obvious luminance degradation and blue shift when they are stored in air, which may come from the decomposition of CsPbI 3 NCs via a simple process assisted by water in air: CsPbI 3 $$\underrightarrow {{{\rm{H}}_2}{\rm{O}}}$$ CsI (aq) + PbI 2 , resulting in a size decrease and thus blue‐shifted PL.…”

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

“…[98,106] Approaches to improve the perovskite/CE energy-level mismatch either aim at the heterogeneous incorporation of hole-extracting materials with a VBM lower than the CEs' WF [99,107] or at the modification of the perovskite's VBM at the perovskite/CE interface. [98,108] The latter approach was adopted by Zhong and coworkers, post-treating a CsPbI 2 Br perovskite film surface with hexyltrimethylammonium bromide (HTAB), which decreased the energy offset between the perovskite and the CE from 0.70 eV in the pristine perovskite to 0.32 eV in the HTAB-treated one, as shown in Figure 8a. [98] This lowered energy mismatch increased the V OC from 1.13 V for the pristine perovskite to 1.20 V for the HTABtreated perovskite in C-PSCs.…”

“…[109] Gong et al increased the VBM of CsPbBr 3 not by surface post-treatment but by adding small amounts of tetra-bisphenol A (TBBPA) in the bulk of the perovskite layer to enhance the hole extraction capability into the CE. [108] In addition, the TBBPA-treated perovskite was characterized by larger grain sizes and fewer trap states than the unmodified one, resulting in PSCs achieving a maximum efficiency of 9.82%. [98] Copyright 2021, Wiley-VCH.…”