Abstract
We synthesized medium-band-gap donor-acceptor (D-A) -type conjugated polymers (PBTZCZ-L and PBTZCZ-H) consisting of a benzotriazole building block as an acceptor and a carbazole unit as a donor. In comparison with the polymers, a small conjugated molecule (BTZCZ-2) was developed, and its structural, thermal, optical, and photovoltaic properties were investigated. The power conversion efficiency (PCE) of the BTZCZ-2-based solar cell devices was less than 0.5%, considerably lower than those of polymer-based devices with conventional device structures. However, inverted solar cell devices configured with glass/ITO/ZnO:PEIE/BTZCZ-2:PC71BM/MoO3/Ag showed a tremendously improved efficiency (PCE: 5.05%, Jsc: 9.95 mA/cm2, Voc: 0.89 V, and FF: 57.0%). We believe that this is attributed to high energy transfer and excellent film morphologies.
Highlights
Π-conjugated small molecules and polymers have attracted considerable attention owing to their light weight, good mechanical flexibility, and compatibility with roll-to-roll printing processes that are potentially applicable to solution-fabricated electronic and optoelectronic devices [1,2,3,4,5]
The power conversion efficiency (PCE) of 11.7% has been obtained for such small molecules by optimizing their molecular structure and device fabrication conditions using an open-circuit voltage (Voc ) of 0.95 V, short-circuit current (Jsc ) of 15.7 mA/cm−2, and fill factor (FF) of 76% [11]
It is known that π-conjugated small molecules possessing a medium optical energy bandgap (Eg ) exhibit high PCEs owing to the complementary broad absorption of fullerene acceptors (PC71 BM) [12]
Summary
Π-conjugated small molecules and polymers have attracted considerable attention owing to their light weight, good mechanical flexibility, and compatibility with roll-to-roll printing processes that are potentially applicable to solution-fabricated electronic and optoelectronic devices [1,2,3,4,5]. The production of π-conjugated small molecules can be scaled-up and high-purity molecules can be obtained [6,7,8] They exhibit good crystallinity and a well-defined chemical structure [9]. It is known that π-conjugated small molecules possessing a medium optical energy bandgap (Eg ) exhibit high PCEs owing to the complementary broad absorption of fullerene acceptors (PC71 BM) [12]. Newly developed π-conjugated small molecules (BTZCZ-2) and polymers containing BTZ building blocks with carbazole units as donor materials were synthesized and characterized for photovoltaic applications. The BTZCZ-2 based device, which shows a wider bandwidth compared to those of the BTZ polymers, possessed a high PCE of 5.05% with Jsc of 9.95 mA/cm , V oc of 0.89 V, and FF of 0.57
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