Dopant‐Free Hole Transporting Materials for Perovskite Solar Cells

Abstract

This article reviews various dopant-free hole transporting materials (HTMs) used in perovskite solar cells (PSCs) in three main categories including inorganic, polymeric, and small molecule HTMs. PSCs have undergone rapid progress, achieving power conversion efficiencies (PCEs) above 22%. With their low production cost and high efficiencies, PSCs are considered promising next-generation solar cell technology. In all developed architectures for PSCs, including planar and mesoscopic with conventional and inverted structures, HTMs play a significant role in determining the photovoltaic performance of PSCs. Using p-type dopants, however, is considered a common strategy to increase the hole conductivity of HTM, which is usually compensated by a more complicated fabrication procedure, higher production costs, and lower stability of PSC. Although several reviews on HTMs have been published, progress on dopant free HTMs needs to be reviewed and analyzed. Here, a review covering most of the published reports on dopantfree HTMs is presented, and the device structure and fabrication method, HTM layer deposition techniques, and the efficiency and the stability of PSCs are addressed during discussions in each main category. Finally, an outlook on stability and PCE growth in PSCs based on dopant-free HTMs is presented.

Defect‐Engineering‐Enabled High‐Efficiency All‐Inorganic Perovskite Solar Cells

“…Like previous halide‐mixed perovskite, light‐induced phase separation has likewise been found in this work (Figure S11, Supporting Information) . Therefore, before getting the J–V plots, light soaking process is needed for all PSCs.…”

High‐Performance Inverted Planar Perovskite Solar Cells Enhanced by Thickness Tuning of New Dopant‐Free Hole Transporting Layer

“…As literatures reported, HTMs can be mainly divided into two types based on their chemical structures. One is that those containing rigid spiro units as cores (such as sprio‐type fluorine, triptycene, and their derivatives), another one is those containing planar units as cores (such as thiophenyl, truxene, phthalocyanine units and other π‐conjugated units, and so on). However, both HTMs have their advantages and limitations.…”

Dopant‐Free Hole‐Transporting Layer Based on Isomer‐Pure Tetra‐Butyl‐Substituted Zinc(II) Phthalocyanine for Planar Perovskite Solar Cells

“…In a conventional n‐i‐p structure, a p‐type hole‐transporting material (HTM), on the top of the perovskite layer, is in contact with a metal back contact . Different categories of organic, polymeric, and inorganic HTMs are developed to collect the photon‐generated holes from the perovskite active layer . To date, 2,2′,7,7′‐tetrakis‐( N , N ‐di‐ p ‐methoxyphenylamine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) is the most studied HTM and the best molecule to achieve highly efficient PSCs with good reproducibility .…”