[6,6]‐Phenyl‐C₆₁‐Butyric Acid Dimethylamino Ester as a Cathode Buffer Layer for High‐Performance Polymer Solar Cells

Abstract

Polymer solar cells (PSCs) have attracted great attention in recent years due to their advantages of low-cost fabrication, light weight, and the capability of being fabricated into fl exible devices. [ 1,2 ] At present, research into PSCs is focused on improvement of the power conversion effi ciency (PCE) and device stability for future applications. The key points for increasing the PCE and stability are the design and synthesis of high-effi ciency photovoltaic materials [ 3,4 ] and the construction of new device structures. With regard to device optimization, great effort has been devoted to the modifi cation of interfacial layers between the electrodes and active layer of PSCs; [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] in particular, solutionprocessable cathode buffer layer materials have become a hot research topic recently. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] Modifi ed interfacial layers can not only improve the photovoltaic performance but also increase the stability of the PSCs. [ 11c , 13a ] Some water-or alcohol-soluble polar polymers have been successfully used as the cathode buffer layer in PSCs, such as poly(ethylene oxide) (PEO), [ 10 ] conjugated polyfl uorene derivatives with the sidechains containing amino end groups (PFN, [ 12,13 ] PFN-Br, [ 14 ] and PSFNBr, [ 15 ] ) or phosphoryl endgroups (PF-EP), [ 16 ] or metal ion-intercalated crown ether (PFCn6:K + ), [ 17 ] and amine-containing polyethylenimine derivatives PEI [ 18,19 ] and PEIE. [ 18 ] Actually, the cathode buffer layer needs to form an ohmic contact between the active layer and the cathode, and to possess lower workfunction and higher electron mobility for effi cient electron collection and transportation to the cathode. From these points of view, fullerene derivatives could be ideal cathode buffer layer materials in considering their n-type semiconductor character, higher electron mobility, and the good energy level matching with the fullerene acceptors (such as [6,6]-phenyl-C61-butyric acid methyl ester (PCBM)) used in the active layer of the PSCs. Therefore, some fullerene derivatives have been synthesized and applied as the cathode buffer layer in PSCs, including self-assembled, [20][21][22][23] cross-linkable, [ 24,25 ] or solvent-orthogonal [ 26,27 ] C 60 derivatives.Considering the success of the water-/alcohol-soluble polar polymers with sidechains attaching amine endgroups and the fullerene derivatives as the cathode buffer layers mentioned above, herein, we design and synthesize two new amine group-modifi ed PCBM derivatives, [6,6]-phenyl-C61-butyric acid 2-((2-(dimethylamino)ethyl)(methyl)amino)ethyl ester (PCBDAN) and [6,6]-phenyl-C61-butyric acid 2-((2-(trimethylammonium)ethyl)(dimethyl)ammonium)ethyl ester diiodonium (PCBDANI) (see Scheme 1 ), and used them as cathode buffer layer materials in PSCs. The selection of [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) derivatives was made in considering the structural and electronic energy level ma...

High‐Performance All‐Polymer Solar Cells Via Side‐Chain Engineering of the Polymer Acceptor: The Importance of the Polymer Packing Structure and the Nanoscale Blend Morphology

“…[ 6,7,10,43 ] The number average molecular weights ( M n = 34-48 kg mol −1 ) and the polydispersity index (PDI) of the PNDIT-HD, PNDIT-OD, and PNDIT-DT polymers were similar, which minimizes the molecular weight effects on the various properties of the polymers. [15][16][17][18][19][20][21] One of the critical issues account for the poor effi ciency is their non-ideal bulk-heterojunction (BHJ) morphology, i.e., large-scale polymer domain size and reduced ordering of polymer chains. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] However, all-PSCs still produce relatively low power conversion effi ciencies (PCEs) of only 3-5%, [3][4][5][6][7][8][9][10][11][12][13] lagging far behind the polymer/fullerene systems with PCEs of 8-10%.…”

“…We described a systematic study of photovoltaic characteristics by fabricating all-PSCs based on their blends with poly [[4,8-bis[5-(2-ethylhexyl) thiophene-2-yl]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fl uoro-2-[(2-ethylhexyl)carbonyl]thieno [3,4-b]thiophenediyl]] (PTB7-Th) polymer donor [ 19,42 ] ( Figure 1 a). [15][16][17][18][19][20][21] One of the critical issues account for the poor effi ciency is their non-ideal bulk-heterojunction (BHJ) morphology, i.e., large-scale polymer domain size and reduced ordering of polymer chains. This desirable fi lm morphology improved the electron mobility (1.3 × 10 −6 → 8.4 × 10 −5 cm 2 V −1 s −1 ) to achieve a well-balanced hole/electron mobility ratio, leading to highly effi cient all-PSCs with PCEs close to 6%, which is the record value reported for all-PSCs thus far.…”

“…We chose NDI unit because NDI-based polymers typically show high electron mobility and have been successfully used as polymer acceptors in all-PSCs. [15][16][17][18][19][20][21] One of the critical issues account for the poor effi ciency is their non-ideal bulk-heterojunction (BHJ) morphology, i.e., large-scale polymer domain size and reduced ordering of polymer chains. Also, the three polymers produced almost identical absorption All-polymer solar cells (all-PSCs) composed of binary blends of conjugated polymer donor/polymer acceptor have attracted signifi cant interest recently, due to their potential advantages over conventional polymer/fullerene solar cells: i) readily tunable molecular energy levels, ii) simultaneous absorption of both polymer donor and polymer acceptor, and iii) enhanced mechanical/thermal properties.…”

Environmentally friendly preparation of nanoparticles for organic photovoltaics

“…[2][3] Undoubtedly, solar energy is one of the best candidates to fulfil the current and future energy needs. [4][5] Organic photovoltaics (OPVs) enjoy significant advantages over traditional solar technology due to their lightweight, flexibility, ease of manufacturing, scalability and low cost. [6][7][8][9] Continued research into OPV technology has led to significant improvements in the device performance with power conversion efficiency (PCE) of up to 13% being reported.…”

Finely Tuned Polymer Interlayers Enhance Solar Cell Efficiency

“…[1,2] For example,i nterlayers located between the active layer and conductive electrodes improve the selectivity of charge transport, and minimize series resistance (R s ), leading to PCE values exceeding 9% for single junction PSCs. [3][4][5][6][7] A blend of poly(ethylenedioxythiophene)a nd poly(styrene sulfonate) (PEDOT:PSS) functions as as olution-processible hole-selective anode modification layer that has proven generally useful for PSCs.R ecent efforts have been devoted to developing new cathode modification layers to enhance electron extraction efficiency.S mall-molecule organic interlayers integrated into PSCs afford noteworthy device improvement, including functional fullerenes, [4,[8][9][10][11][12][13][14][15][16] perylene diimides, [17] and oligomeric fluorenes. [5] Polymer interlayers provide advantages of both facile solution processing and robust film formation, with two recently reported examples being poly(ethyleneimine) (PEI) [18,19] and tertiary-aminesubstituted polyfluorene (PFN).…”