n-Type Water/Alcohol-Soluble Naphthalene Diimide-Based Conjugated Polymers for High-Performance Polymer Solar Cells

Abstract

With the demonstration of small-area, single-junction polymer solar cells (PSCs) with power conversion efficiencies (PCEs) over the 10% performance milestone, the manufacturing of high-performance large-area PSC modules is becoming the most critical issue for commercial applications. However, materials and processes that are optimized for fabricating small-area devices may not be applicable for the production of high-performance large-area PSC modules. One of the challenges is to develop new conductive interfacial materials that can be easily processed with a wide range of thicknesses without significantly affecting the performance of the PSCs. Toward this goal, we report two novel naphthalene diimide-based, self-doped, n-type water/alcohol-soluble conjugated polymers (WSCPs) that can be processed with a broad thickness range of 5 to 100 nm as efficient electron transporting layers (ETLs) for high-performance PSCs. Space charge limited current and electron spin resonance spectroscopy studies confirm that the presence of amine or ammonium bromide groups on the side chains of the WSCP can n-dope PC71BM at the bulk heterojunction (BHJ)/ETL interface, which improves the electron extraction properties at the cathode. In addition, both amino functional groups can induce self-doping to the WSCPs, although by different doping mechanisms, which leads to highly conductive ETLs with reduced ohmic loss for electron transport and extraction. Ultimately, PSCs based on the self-doped WSCP ETLs exhibit significantly improved device performance, yielding PCEs as high as 9.7% and 10.11% for PTB7-Th/PC71BM and PffBT4T-2OD/PC71BM systems, respectively. More importantly, with PffBT4T-2OD/PC71BM BHJ as an active layer, a prominent PCE of over 8% was achieved even when a thick ETL of 100 nm was used. To the best of our knowledge, this is the highest efficiency demonstrated for PSCs with a thick interlayer and light-harvesting layer, which are important criteria for eventually making organic photovoltaic modules based on roll-to-roll coating processes.

High‐Performance Polymer Tandem Solar Cells Employing a New n‐Type Conjugated Polymer as an Interconnecting Layer

“…Herein, we employed a newly developed amine-containing conjugated polymer PF3N-2TNDI [ 37,38 ] as the ETL and PEDOT:PSS as the HTL to construct the ICL for conventional tandem OSCs. A 2 nm Ag fi lm was deposited to further improve the recombination property at the ETL/HTL interface.…”

“…[ 32 ] The effect of the ICL on the tandem cell performance was evaluated by choosing two different types of amine-containing polymers as the ETL, including the most commonly used polyfl uorene-based ETL, poly[(9,9-bis(3′-( N,N -dimethylamino)-propyl)-2,7-fl uorene)-alt -2,7-(9,9-dioctylfl uorene)] (PFN), [ 43 ] and our newly designed PF3N-2TNDI, whose backbone is composed of the fl uorene and naphthalene diimide (NDI) units conjugated by two thiophene spacers. [ 37,38 ] The new design was aimed to improve the electron mobility of the ETL as the NDI-based polymers are known to possess good electron transporting property. PFN is one the most successful ETLs used for cathode modifi cation in both OSCs and organic light emitting diodes.…”

Thieno[3,4‐c]Pyrrole‐4,6‐Dione‐Based Polymer Acceptors for High Open‐Circuit Voltage All‐Polymer Solar Cells

“…In turn, while BHJ solar cells composed of polymer donors and fullerene acceptors can achieve power conversion efficiencies (PCEs) >11%, [3][4] only a few polymer acceptors have been shown to yield BHJ device PCEs >5% thus far. [5][6][7][8][9][10] The lack of morphological stability and mechanical conformability of fullerene-based BHJ solar cells justifies the development of nonfullerene replacements, including polymer acceptors.…”

Insights into the working mechanism of cathode interlayers in polymer solar cells via [(C8H17)4N]4[SiW12O40]

“…This limitation is a big challenge to reproducibly process such ultrathin CILs with good uniformity over large areas without forming pinholes. Even though doping of the materials can increase their conductivities and thicknesses in PSCs, 10,27 the absorption of thicker CIL lms in the visible region is usually not negligible, which diminishes the photocurrent. Therefore there is an urgent need to develop and design environmentally friendly, low cost, and transparent CIL materials which have sufficient conductivity for electrons for large-area roll to roll production of PSCs.…”