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1 Supporting nline Material for High-Detectivity Polymer Photodetectors with Spectral Response from 300 nm to 1450 nm Xiong Gong,* Minghong Tong, Yangjun Xia, Wanzhu Cai, Ji Sun Moon, Yong Cao,* Gang Yu, Chan-Long Shieh, Boo ilsson, Alan J. Heeger* *To whom correspondence should be addressed. (X.G.); (Y.C.); (A.J.H) This PD file includes: Materials and Methods igs. S1 to S3 Table S1 Scheme S1 References Published 13 August 2009 on Science Express DI: /science

2 1. Geometry-optimized density functional calculations All the calculations were done using Gaussian 03. irst, the structure of PDDTT is geometrically optimized in two steps (for the calculations, the polymer is assumed to be planar and the alkyl chains are not included in the structure). 1. The pre-optimizing method is Hartree-ock. The basis set is 6-31G; the calculations use Density unctional (DT) Methods. The basis set is also 6-31G. Polymer structures were optimized with one monomer, two monomers and three monomers. 2. The excited state energies were calculated using the Zindo semi-empirical method and, alternatively, DT. The basis set is 6-31G*. Three excited state energies were calculated using each of the methods; the results are shown in igure S1, where is the number of monomers in the optimized repeat unit. The intercept on y axis corresponds to the absorption edge. Table S1 summarizes the results. The DT method yields better agreement with the experiment results. Therefore, the calculated onset absorption wavelength of PDDTT is 1450nm. Single Excited State Energy (ev) 1.6 DT Zindo /n igure S1. The first excited state energy versus 1/n where n is the number of monomer units in the oligomer

3 Table S1. Summary of calculation results Method Zindo DT Absorption edge 2587 (nm) 1450 (nm) 2. Molecular structures of PVK, C60 and PS-TPD-PCB n PVK C60 m n Bu Bu Bu Bu n m PS-TPD-PCB Scheme S1. Molecular structures of PVK, C60 and PS-TPD-PCB

4 3. Time Resolved Photoinduced Absorption and Transient Photoconductivity To better understand the 200-fold increase in photocurrent in PDDTT:PC 60 BM composite compared to pristine PDDTT, we have studied the carrier photogeneration and decay in PDDTT:PC 60 BM composites using transient absorption (TA) spectroscopy in the visible through mid-ir spectral range. igure S2a shows the ultrafast TA spectra of pristine PDDTT thin film and PDDTT:PC 60 BM composite thin films probed between 550 nm and 1070 nm; the data are normalized at the 625 nm peak. The excitation wavelength was 800nm where there is negligible absorption from PC 60 BM. The TA spectrum of pristine PDDTT film shows a photoinduced absorption (PA) band around 625 nm and a photobleaching (PB) band above 720 nm. or PDDTT:PC 60 BM, the TA spectrum below 880nm shows similar features to that of pristine PDDTT. However, a new PA band was observed in the TA spectrum at wavelengths near 1000 nm. Since there is no direct photoexcitation from PC 60 BM when pumped at 800 nm, this long wavelength PA band indicates the formation of a photoexcitation resulting from the interaction between PDDTT and PC 60 BM. Since the absorption of the PC 60 BM radical anion is at 1020nm (S1), we ascribe the new PA band to the PC 60 BM radical anions created by electron transfer from excited PDDTT to PC 60 BM. ote that the PC 60 BM radical anion PA band appears within 0.5ps, indicating ultrafast photoinduced electron transfer. The ultrafast electron transfer is the origin of the efficient photoinduced charge separation and high photocurrent in PDDTT:PC 60 BM. igure S2b compares the dynamics of the PA in pristine PDDTT and in the PDDTT:PC 60 BM composite thin films probed at 4.7μm. In this mid-ir spectral region, where the polarons from the π-conjugated polymers can be detected (S2), we observed

5 very fast decay in PDDTT but much longer lifetime in the PDDTT:PC 60 BM thin films. The much longer polaron lifetime (nanoseconds) in the composite compared to that in the pristine polymer indicates long-lived carriers, consistent with efficient charge transfer from PDDTT to PC 60 BM with inhibited back-transfer (S3). The mobile carrier decay (photocurrent decay) at longer times was also studied using transient photocurrent measurements. igure S2c shows the normalized transient photocurrent (PC) response (prior to time decay) for PDDTT and for the PDDTT:PC 60 BM composite. The charge carrier decay in pristine PDDTT is very fast and cannot be time resolved with our measurement system (100 ps temporal resolution). The long-lived photocurrent, τ 3.3ns, observed in the composites is consistent with efficient ultrafast charge transfer and charge separation. We have also used λ=400 nm as pump source to excite both PDDTT and PC 60 BM. Similar PA and photocurrent action spectra (characteristic of mobile carriers) were observed. All these results indicate ultrafast photo-induced charge transfer from PDDTT to PC 60 BM. The ultrafast charge transfer, efficient charge separation and long mobile carrier lifetime result in the high photocurrent observed in PDDTT:PC 60 BM composites.

6 10 2 ( ΔΤ/Τ) Pump: 800nm; t=0.5ps PDDTT PDDTT: PC 60 BM Wavelength (nm) ΔΤ (arb. units) b Pump: 800nm, Probe: 4.7μm PDDTT PDDTT:PC 60 BM Time (ps) ormalized PC c PDDTT PDDTT:PC 60 BM Time (ns) igure S2: (a) Transient absorption spectra of PDDTT and PDDTT: PC 60 BM (normalized at the 625 nm peak) at 0.5ps delay time after 800nm excitation. (b) Mid-IR transient decay dynamics of PDDTT and PDDTT: PC 60 BM probed at 4.7μm. (c) ormalized transient PC (peak response prior to time decay) for PDDTT and PDDTT: PC 60 BM.

7 4. ormulation of PEDT and Device abrication ormulation of PEDT: the PEDT was formulated by adding 2 ml alcohol into 1mL poly(3,4-ethylene dioxythiophene): poly(styrene sulfonic acid) (PEDT:PSS) (CH8000) and then stirring over night. Device abrication: the device configuration is (IT)/PEDT/PDDTT:PC 60 BM/Al. ormulated PEDT was spin-cast onto pre-cleaned IT coated glass. The thickness of PEDT is less than 10nm. The active layer, PDDTT:PC 60 BM (1:2 by weight) was then spin-cast onto the PEDT layer. The film thickness is approximately 150nm. The Al cathode was deposited through a shadow mask by thermal evaporation at 4 x 10-7 Torr. 5. AM images PDDTT:PC 60 BM/PEDT/IT

8 PDDTT:PC 60 BM/IT igure S3. AM images of PDDTT:PC 60 BM thin films on top of IT and PEDT/IT S1. Guldi D. M., Prato M., Excited-State Properties of C 60 ullerene Derivatives. Acc. Chem. Res. 33, (2000). S2. Sheng C. X., Tong M. H., Singh S., Vardeny Z. V., Experimental determination of the charge/neutral branching ratio in the photoexcitation of -conjugated polymers by broadband ultrafast spectroscopy. Phys. Rev. B. 75, (2007). S3. Lee C. H., Yu G, Moses D., Pakbaz K., et al., Sensitization of the photoconductivity of conducting polymers by C 60 : Photoinduced electron transfer. Phys. Rev. B. 48, (1993).