Morphologic improvement of the PBDTTT-C and PC₇₁BM blend film with mixed solvent for high-performance inverted polymer solar cells

Abstract

Tracing the evolution of the bulk heterojunction structure, a dramatic promotion in the efficiency of polymer solar cells has been obtained in recent years. The active layer morphology of low-bandgap polymer solar cells is one of the critical factors for high-efficiency performance. In the past, the relationship between morphology improvement and the device's characteristics (such as efficiency, fill factor and short-circuit current) in low-bandgap polymer solar cells has been studied intensively with regards to the conventional structure. Here we demonstrate the morphologic improvement of the poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b;4,5-b']dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiopene)-2,6-diyl]/[6,6]-phenyl C71 butyric acid methyl ester (PBDTTT-C/PC71BM) blend film for inverted solar cells. By utilizing a mixed solvent of dichlorobenzene/chlorobenzene with (1,8-diiodooctane) additives, the device efficiency can be significantly enhanced, from 0.92% to 4.43%. This enhancement is attributed to active layer morphologic improvement promoting carrier transport. Furthermore, the thickness optimization of the active layer and the electron blocking layer MoO3 further contributes to efficiency. The device performance could be achieved with an efficiency as high as 5.35%, an open-circuit voltage of 0.70 V, a short-circuit current density of 13.5 mA cm(-2), and a fill factor of 57%.

A two-step strategy to clarify the roles of a solution processed PFN interfacial layer in highly efficient polymer solar cells

“…27,44,45 The interfacial dipole layer is beneficial to increase the built-in field, resulting in the increased V OC of PSCs. [47][48][49] Therefore, the working solvents have a relatively fast volatilization process compared with the DIO additive from the active layers. S7.…”

Tuning nanoscale morphology using mixed solvents and solvent vapor treatment for high performance polymer solar cells

“…[23][24][25] However, the morphology of active layer including narrow band gap polymer is hardly adjusted by thermal annealing treatment due to its poor self-packaging characteristic. 26,27 Recently, Liang et al reported an efficient method to adjust the active layer morphology by adopting mixed solvent approach. 28 Dou et al also reported that the PCE of PSCs was increased to 5.8% from 1.5% by using 1,8-diiodoctane (DIO) as solvent additive based on a blend lm composed of poly{2,6 0 -4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,4-b]dithiophene-alt-5dibutyloctyl-3,6-bis…”

Formulation strategies for optimizing the morphology of polymeric bulk heterojunction organic solar cells: a brief review

“…CN is another material that has been used as a processing additive, 94,95 but unlike other processing additives such as DIO or ODT, CN is a good solvent for the fullerene derivative (e.g., the solubility of PC 71 BM in CN was reported to be above 400 mg mL −1 ) 81 and is known for being a good solvent for aromatic polymers. 76 In other D:A blends, CN was found to reduce the aggregation of polymers.…”