Elucidating the Roles of Hole Transport Layers in p‐i‐n Perovskite Solar Cells

Abstract

The hole‐transport layer (HTL) is critical to high performance of perovskite solar cells (PSCs) in terms of hole extraction, transportation, and mediation of the following film formation. Here, the interplay between HTLs and open‐circuit voltage (VOC) in PSCs is directly targeted. The results suggest that there is no evident relation between the obtained VOC and the work function of HTLs and it is directly controlled by the recombination losses inside the perovskite material (grain boundaries and trap states) as well as at the interfacial contacts. Additionally, an insight understanding about the charge transfer behavior in PSCs is provided and it is pointed out that the nature of interfacial contacts is a critical factor in defining charge accumulation and recombination at the interfaces. Analysis of the electroluminescence efficiency and transient absorption spectroscopy confirms the better interfacial contact of HTL/perovskite, and larger grain size of perovskite films mediated by the hydrophobic nature of HTLs can collectively and efficiently eliminate nonradiative recombination, resulting in faster charge transfer and lower resistance at the interfaces. This work provides a profound understanding of how the surface hydrophobicity and the interface contact are correlated in terms of nonradiative losses and J–V characters in real devices.

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

“…As far as the authors know, the PCE of 18.17% with negligible hysteresis is one of the best performances achieved by solution-processed MAPbI 3 -based inverted PSCs with dopant-free D-A polymeric HTM. [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).…”

“…[2][3][4] For good performance of inverted p-i-n PSCs, holetransporting materials (HTMs) not only play an indispensable role in hole extraction and transfer from the perovskite layer to the electrode, but also have an important influence on the crystallization of the perovskite film, which could significantly enhance the optoelectronic properties and PCEs of the devices. [5][6][7] The most commonly used HTMs for inverted planar PSCs are poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and poly[bis(4-phenyl)(2,4,6-trimethylphenyl) amine] (PTAA). [8,9] Although PEDOT:PSS has high electrical conductivity and excellent solution processability, its acidic and…”

“…Moreover, the efficiencies of inverted p-i-n devices still lag behind those of n-i-p ones using the dopant-free D-A-structured polymeric HTMs, which is due to the lower short current densities ( J sc ) and/or larger open-circuit voltage (V oc ) losses induced by nonradiative recombination. [33,34] At 18.34%, the highest PCE of p-i-n PSCs (indium tin oxide (ITO)/HTM/ (FAPbI 3 ) 0.85 (MAPbBr 3 ) 0.15 /PC 61 BM/BCP/Ag) with a D-A-structured polymeric dopant-free HTM, in this case, poly((E)-6-(5 0 0 0 -hexyl-5 0 -(5 0 0 0 -hexyl-5 0 0 -(5-hexylthiophen-2-yl)-[2,2 0 :3 0 ,2 0 0 :4 0 0 , 2 0 0 0 -quaterthiophen]-5 0 -yl)-5 0 0 -(5-hexylthiophen-2-yl)-[2,2 0 :3 0 ,2 0 0 :4 0 0 , 2 0 0 0 -quaterthiophen]-5-yl)-1,1 0 -bis(2-octyldodecyl)-[3,3 0 -biindolinylidene]-2,2 0 -dione (PII2T8T), is almost 3% lower than that of otherwise n-i-p PSCs (fluorine-doped tin oxide (FTO)/ SnO 2 /Cs 0.06 FA 0.78 MA 0.16 Pb 0.94 I 2.4 Br 0.48 /HTM/Au) using alkoxy-poly(4-([2,2 0 -bithiophen]-5-yl)-7-(5-(4,8-bis (5-(2-ethylhexyl) thiophen-2-yl)-6-(thiophen-2-yl)benzo [1,2- [1,2,5]thiadiazole) (PTEG). [29,30] This and other examples in the literature suggest that there is room for further development of a dopant-free D-A-structured polymeric HTM to realize highly efficient and stable inverted PSCs for commercialization.…”

Tris(pentafluorophenyl)borane‐Modified P3CT‐K as an Efficient Hole‐Transport Layer for Inverted Planar MAPbI3 Perovskite Solar Cells

“…The advancement of perovskite solar cells (PSCs) stands out from the emerging photovoltaic devices attributed to the excellent properties of perovskite materials and the promising large-scale manufacturing, especially at an eye-catching speed of promoting their power conversion efficiencies (PCEs) exceeding 25% in a decade. [1][2][3] Configuration wise, the inverted and thoroughly solve the aggregation problem, and it is very little involvement in the current HTL study in inverted planar perovskite solar cell. Furthermore, it still remains ambiguous to understand the mechanism of main-chain modification for CPEs via intermolecular interaction.…”

Research Progress of Hole Transport Materials Based on Spiro Aromatic-Skeleton in Perovskite Solar Cells

“…鉴于有机-无机杂化钙钛矿材料的本征半导体特性, 钙钛矿电池主要采用平面异质结架构, 器件特点是结构 简单、稳定性好、光电转换效率高. 平面异质结器件包 括: n-i-p 正型结构(即电子传输层-钙钛矿层-空穴传输层 结构) [19][20] 和 p-i-n 反型结构(空穴传输层-钙钛矿层-电子 传输层的结构) [21][22][23] . n-i-p 型是目前最典型的钙钛矿电 池结构, 优点是能有效地抑制回滞现象, 减少电荷复合, 从而提升器件效率和稳定性 [24] .…”