Nonfullerene Electron Transporting Material Based on Naphthalene Diimide Small Molecule for Highly Stable Perovskite Solar Cells with Efficiency Exceeding 20%

Abstract

This study reports a new nonfullerene electron transporting material (ETM) based on naphthalene diimide (NDI) small molecules for use in high-performance perovskite solar cells (PSCs). These solar cells simultaneously achieve high power conversion efficiency (PCE) of over 20% and long-term stability. New NDI-ID (N,N′-Bis(1-indanyl)naphthalene-1,4,5,8-tetracarboxylic diimide) consisting of an N-substituted indane group having simultaneous alicyclic and aromatic characteristics is synthesized by a low-cost, one-step reaction, and facile purification method. The partially flexible characteristics of an alicyclic cyclopentene group on indane groups open the possibility of lowtemperature solution processing. The conformational rigidity and aromaticity of phenyl and alicyclic groups contribute to high temporal stability by strong secondary bonds. NDI-ID has herringbone packed semiconducting NDI cores that exhibit up to 0.2 cm 2 V −1 s −1 electron mobility in field effect transistors. The inverted PSCs based on CH(NH 2 ) 2 PbI 3-x Br x with NDI-ID ETM exhibit very high PCEs of up to 20.2%, which is better than that of widely used PCBM (phenyl-C61-butyric acid methyl ester) ETM-based PSCs. Moreover, NDI-IDbased PSCs exhibit very high long-term temporal stability, retaining 90% of the initial PCE after 500 h at 100 °C with 1 sun illumination without encapsulation. Therefore, NDI-ID is a promising ETM for highly efficient, stable PSCs.

Homochiral Asymmetric‐Shaped Electron‐Transporting Materials for Efficient Non‐Fullerene Perovskite Solar Cells

“…)o fN DI-PhE ETM is similar to that of the previously reported N,N'-bis(1-indanyl)naphthalene-1,4,5,8-tetracarboxylic diimide( NDI-ID)f or highly efficient PSCs with PCEs exceeding2 0%. [30] In general, the in-planee lectron-transport directioni so ptimal for FETs, whereas the normal direction of electron transport is optimal for PSCs. [34,54,55] These results imply that three-dimensionally isotropic or well-balanced electron transporti nE TMs is more critical than just ah igh value of in-plain electron mobility for reliable PSC operation.…”

“…[21][22][23][24][25] In contrast, only af ew classes of electron-transporting materials (ETMs)b ased on small molecules have been reported. [26][27][28][29][30] In anothera pproach, electron transporting layer-free PSCs have been reported. [31] Of the reported small-molecule ETMs, fullerene and its derivatives, such as C 60 , phenyl-C 61 -butyric acid methyl ester (PCBM), and indene-C 60 -bisadduct (ICBA), have been used as standard electron transporters not only for their optimal energyl evel alignment with per-Ad esign strategy is proposed for electron-transporting materials (ETMs)w ith homochiral asymmetric-shaped groups for highly efficient non-fullerene perovskite solar cells (PSCs).…”

Non‐Fullerene Organic Electron‐Transporting Materials for Perovskite Solar Cells

“…However, their poor film‐forming ability and low solubility need to be improved. As is the case with polymeric ETMs, efficient semiconducting n‐type cores can be introduced into small‐molecule ETMs for incorporation into inverted PSCs …”

“…Other solution‐processable small‐molecule ETMs include NDI‐based ETMs. As shown in Figure , NDI‐based small‐molecule ETMs with N‐substituents can be synthesized in a one‐pot reaction with an overall yield of approximately 50 % . Similar to azaacene‐based ETMs, N‐substituted NDI‐based ETMs exhibit high solubility in dichlorobenzene and can be coated on the perovskite layer through solution processing.…”

“…Similar to azaacene‐based ETMs, N‐substituted NDI‐based ETMs exhibit high solubility in dichlorobenzene and can be coated on the perovskite layer through solution processing. These exhibit high PCE values of >20 % and high temporal stability owing to their high crystallinity and thermal stability . In addition to N‐substituents on NDI‐based small‐molecule ETMs, chemical modification of the π‐conjugated structure of the NDI core has been reported .…”