Tuning the Polarizability in Donor Polymers with a Thiophenesaccharin Unit for Organic Photovoltaic Applications

Abstract

1 www.MaterialsViews.com wileyonlinelibrary.com of the relationship between polymeric structure of the donor material and device performance. Among the factors that may infl uence solar energy conversion, the nature of electron donating and accepting materials and the morphology of the composites play the crucial roles in determining the fi nal performance of the devices. In recent years, fullerene derivatives such as [6,6]-phenyl C 71 -butyric acid methyl ester (PC 71 BM) have been widely adopted as electron acceptors due to their low lying energy levels and relatively high electron affi nity and mobility. It was also found that addition of a small amount of high boiling point solvent, generally 1,8-diiodooctane (DIO), can reliably improve the morphology of most of the composite systems. [ 19,20 ] Thus, we focus our main effort on understanding the structure/property correlation of electron donor materials in order to develop innovative strategies for achieving high performance solar cells.Numerous factors can infl uence the optical and electrical properties of low bandgap polymers. Our previous research indicated that the calculated internal dipole moment change between the ground and excited states of a polymer's repeating units, Δµ ge , showed a linear correlation with solar cell performance when other factors, such as morphology and charge carrier mobility, are comparable. [ 21,22 ] Crucial questions to be answered are that what will happen when Δµ ge is further increased, and why such a phenomenological model works well in a certain range. In this paper, calculations of dipolar change based on the polymer repeating units led us to identify two polymer systems, both copolymers containing benzodithiophene (BDT). One is based on thieno[3,4-c]pyrrole-4,6-dione (TPD) and the other on 3-oxothieno[3,4-d ]isothiazole 1,1-dioxide (TID). The TPD unit has recently been incorporated into various low band gap conjugated polymer systems. [23][24][25] Previously explored as an artifi cial sweetener, TID unit bears both a sulfonyl and a carbonyl group, and is more electron defi cient than TPD. The calculation results showed that the repeating units of both polymers containing TPD and TID (PPB and PID, respectively) exhibit a larger Δµ ge than our previous champion polymer PTB7. Thus, two polymers, PPB and PID, were synthesized and characterized Tao Tuning the Polarizability in Donor Polymers with a Thiophenesaccharin Unit for Organic Photovoltaic Applications

Recent Advances in Wide‐Bandgap Photovoltaic Polymers

“…The new TID unit was similar to the well‐studied TPD unit, except that one carbonyl was replaced by a sulfonyl group, and it was more electron deficient than TPD. It was observed that the strong electron‐withdrawing sulfonyl group was detrimental to charge separation, which resulted in moderate PCEs of 3.28 and 3.05% for P96 and P97 , respectively …”

“…Furthermore, P97 was mixed with the PTB7:PC 71 BM blend . Although the PCE of P97 binary cells was only 2.01%, an encouraging PCE of 8.22% was exhibited when 10% P97 content was added into the binary system; the absorption was enhanced at short wavelengths, and charge transfer was favored by the cascaded frontier energy levels of P97 .…”

Synthesis and properties of low band gap polymers based on thienyl thienoindole as a new electron-rich unit for organic photovoltaics

“…The spectral mismatch factor was calculated by comparison of solar simulator spectrum with AM 1.5 spectrum at room temperature. (2). A 500 mL round-bottom flask, equipped with a magnetic stirring bar and a dropping funnel was charged with water (38 mL).…”

Match the Interfacial Energy Levels between Hole Transport Layer and Donor Polymer To Achieve High Solar Cell Performance

“…4, 22 We show that by proper energy level alignment between HOMO of donor polymer and work function of HTL, 106% enhancement of PCE could be achieved.…”