Modulate Molecular Interaction between Hole Extraction Polymers and Lead Ions toward Hysteresis‐Free and Efficient Perovskite Solar Cells

Abstract

Herein three polymeric hole extraction materials (HEMs), poly(benzene‐dithiophene) (PB2T)‐O, PB2T‐S, and PB2T‐SO are presented for p–i–n perovskite solar cells (PVSCs). This study reveals that the perovskite device hysteresis and performance heavily rely on the perovskite grain boundary conditions. More specifically, they are predetermined through the molecular interaction between Lewis base atoms of HEMs and perovskites. It is revealed that only changing the side chain terminals (OCH3, SCH3, and SOCH3) of HEMs results in effective modulating PVSC performance and hysteresis, due to the effective tune of interaction strength between HEM and perovskite. With an in situ grown perovskite‐HEM bulk heterojunction structure, PB2T‐O with weak binding group (OCH3, −78.9 kcal mol−1 bonding energy) to lead ions allows delivering hysteresis‐free and efficient devices, which is sharp contrast to the strong binding PB2T‐SO (−119.3 kcal mol−1 bonding energy). Overall, this work provides new insights on PVSC hysteresis and the related curing methods via multifunctional HEM design in PVSCs.

Dopant‐Free Ternary Conjugated Polymeric Hole‐Transporting Materials for Efficient Inverted Planar Perovskite Solar Cells

“…[5][6][7][10][11][12][13]31,32] Table 3 lists photovoltaic parameter data of the conventional MAPbI 3 perovskite devices using best performing dopant-free polymer HTMs. The solar cell based on our A 1 -D-A 2 -D-type terpolymer PDPPTBT as HTM approaches the recorded PCE reported to date for both p-i-n-and n-i-p-structured PSCs with a conventional MAPbI 3 perovskite absorption layer and a dopant-free polymer HTM layer, [26,31,[52][53][54][55][56] which is matched to the benchmark devices based on the widely used polymer HTM PTAA without doping treatments (with 19.4% efficiency). [57] The external quantum efficiencies (EQEs) of devices based on these polymeric HTMs are show in Figure 5c.…”

A Reversible Structural Phase Transition by Electrochemically-Driven Ion Injection into a Conjugated Polymer

“…The synthesis and characterization of PB2T-TEG is described in the Supporting Information, which also includes cyclic voltammetry, absorption spectra, and thermogravimetric analysis of PB2T-TEG (Figure S1 and Figure S2). Derivatives of PB2T-TEG have been used previously as hole extraction materials in lead halide perovskite solar cells Figure B shows cyclic voltammetry (CV) sweeps of PB2T-TEG in 100 mM KCl, indicating that the polymer is indeed electrochemically active in electrolyte solution, with an oxidation onset of +0.2 V relative to Ag/AgCl (Figure B).…”

“…Derivatives of PB2T-TEG have been used previously as hole extraction materials in lead halide perovskite solar cells. 39 Figure 1B shows cyclic voltammetry (CV) sweeps of PB2T-TEG in 100 mM KCl, indicating that the polymer is indeed electrochemically active in electrolyte solution, with an oxidation onset of +0.2 V relative to Ag/AgCl (Figure 1B). The spectroelectrochemistry measurements in Figure 1C show a nearly complete bleach by +0.4 V relative to Ag/AgCl, indicating that PB2T-TEG can be rapidly oxidized throughout the entire volume of the polymer with a time constant of 530 ± 20 ms (Figure S3).…”

Carbon-based materials for stable, cheaper and large-scale processable perovskite solar cells

“…2 Graphite-and carbon black-based back electrodes Generally speaking, a PSC is based on a perovskite layer 48,49 sandwiched between an ETM and a HTM. 50,51 The ETM usually consists of TiO 2 or another n-type semiconductor anode, [52][53][54] while the back electrode is deposited on top of the HTM. [55][56][57] For efficient charge extraction, the valence band (VB) and the conduction band of the perovskite should lie below the highest occupied molecular orbital (HOMO) of the HTM and under the lowest unoccupied molecular orbital (LUMO) of the ETM, respectively.…”