Impact of the Alkyl Side Chains on the Optoelectronic Properties of a Series of Photovoltaic Low-Band-Gap Copolymers

Abstract

The design of novel low-band-gap conjugated polymers with appropriate frontier orbital energy levels and good charge transport is needed to improve the conversion efficiency of organic photovoltaic devices. In this article, we describe the synthesis and structure−property relationships of a series of photovoltaic copolymers with a common conjugated backbone and differing solubilizing side chains. The copolymer optoelectronic properties and the related photovoltaic device performances are reported. Our results clearly show that the side chains have a major impact on the material and device properties. The electronic band gap can be varied by more than 0.3 eV, the charge mobilities by orders of magnitude, and the optimized fullerene content of photovoltaic devices by a factor of 4 by barely changing the side-chain positioning and/or by switching from linear to branched alkyl chains. A power conversion efficiency of 2.7% could be achieved with devices using the most promising polymer.

Structure‐Property Optimizations in Donor Polymers via Electronics, Substituents, and Side Chains Toward High Efficiency Solar Cells

“…The PBDT-DTBT series demonstrates that the optimum location for side chains should cause the least steric disturbance to the planarity of the polymer backbone. [ 84,85 ] In this series, PBDT-4DTBT, which is alkylated at the four-position of the thienyl groups, exhibited the highest effi ciency in its BHJ solar cells (Table 7 ). Similar to the control polymer Table 7.…”

Factors Governing Intercalation of Fullerenes and Other Small Molecules Between the Side Chains of Semiconducting Polymers Used in Solar Cells

“…Likewise, Heiser recently reported that branched side chains appear to inhibit intercalation in PTBzT 2 blends (based on optimization of power conversion effi ciencies). [ 44 ] PTBzT 2 -β is identical to PBTTT-C12 except for the addition of a benzothiadiazole group between the two unfused thiophene rings, so it is not surprising for fullerene intercalation to occur in PTBzT 2 -α and PTBzT 2 -β .The fact that branched side chains appear to inhibit intercalation in both PBTTT and PTBzT 2 may have implications for the highest performing polymers, since many of them contain branched side chains. [45][46][47][48][49][50] Still, it remains unclear how side-chain branching affects molecular mixing in amorphous domains.…”

Improved Solubility and Characterization of Photovoltaic Properties D/A Copolymers based on Rigid Structure of Phenothiazine-Quinoxaline

“…이러한 효율은 기존 실리콘태양전지에 비해 매우 낮은 수준이며 상업적으로 성공하 기 위해선 최소 10%대 이상의 효율을 나타내어야 하는 것으로 보고되고 있다 [8][9][10][11]. 이에 따라 높은 광전변환효율과 안정성 을 확보하기 위해 전자주개 물질로 공액 고분자와 전자받개 물질로 fullerene의 유도체인 PCBM을 혼합한 이종접합형태 (bulkheterojunction, BHJ)구조에 대한 개발이 활발히 진행 중이 며, 8-10%대의 고효율의 구조도 보고되고 있다 [12][13][14].…”