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Increase of internal quantum eciency in small molecular oligothiophene:C60 mixed heterojunction solar cells by substrate heating Supplemental Material D. Wynands,∗ M. Levichkova, K. Leo, and M. Riede Institut für Angewandte Photophysik, Technische Universität Dresden, 01062 Dresden, Germany C. Uhrich, G. Schwartz, D. Hildebrandt, and M. Pfeier Heliatek GmbH, 01139 Dresden, Germany (Dated: August 18, 2010) I. ADDITIONAL DEVICES In addition to the devices presented in the paper we investigated two additional devices (D and E) with a mixed layer thickness of xD =xE =20 nm. The structure is the same as of devices 3 0 2 5 n o n h e a D A h e a te d E B C C u r r e n t d e n s ity ( m A /c m 2 ) 2 0 1 5 1 0 te d d e (2 0 n m (3 0 n m d e v ic e (2 0 n m (3 0 n m (4 0 n m v ic e s : ) ) s : ) ) ) 5 0 -5 -1 0 -1 5 -0 .5 0 -0 .2 5 0 .0 0 0 .2 5 0 .5 0 0 .7 5 1 .0 0 V o lta g e ( V ) FIG. 1: Current-voltage characteristics of devices A to E. For performance parameters see Table I. ∗ Electronic address: [email protected]; URL: http://www.iapp.de 2 TABLE I: Performance parameters of devices A to E. device Voc (V) jsc (mAcm−2 ) FF I (mWcm−2 ) ηPCE (%) A 0.88 7.3 0.422 126.0 2.1±0.1 B 0.89 10.9 0.607 119.3 4.9±0.2 C 0.88 11.6 0.570 117.7 4.9±0.2 D 0.89 7.1 0.503 128.2 2.5±0.1 E 0.90 9.7 0.640 125.9 4.4±0.2 A to C: ITO / n-C60 (5)/ C60 (15)/ DCV6T:C60 (x, Tsub )/ BPAPF (5)/ p-BPAPF (10)/ p-Di-NPD (30)/ NDP9 (1)/ Al (100). Device D was produced without substrate heating (Tsub =30 ◦ C), whereas device E was heated to a substrate temperature of approximately 90 ◦ C during the deposition of the mixed layer. Mixing ratio of the DCV6T:C60 HJ is 2:1 by volume. Mixed layer thickness of devices A to E is xA =30 nm, xB =30 nm, xC =40 nm, xD =20 nm, xE =20 nm, respectively. Fig. 1 presents the current-voltage characteristics of all investigated devices. Performance parameters are summarized in Table I. Due to to the smaller mixed layer thickness of the additional devices D and E they exhibit smaller short circuit currents (D: 7.1 mAcm−2 , E: 9.7 mAcm−2 ) than corresponding devices, but are characterized by a slightly higher ll factor (D: 0.503, E: 0.640). The enhanced power conversion eciency (PCE) of device E compared to device D underlines the positive eect of substrate heating. In Fig. 2 IQE spectra of the heated devices B, C, and E are shown. As stated in the paper all devices exhibit nearly equal IQE despite their dierence in mixed layer thickness. This shows that ηcc has no observable limiting eect on the IQE upon the investigated interval. We therefore assume that the mixed layer morphology achieved by substrate heating is considerably optimized. II. ADDITIONAL CHECK OF POWER CONVERSION EFFICIENCY To conrm the determined PCE of device B and C we conducted outdoor measurements on the balcony of our institute (51 ◦ 3'N, 13 ◦ 44' 24"E) on 09.08.2009. An aperture of 2.985 mm2 was used. Intensity of sun irradiation was 99 mWcm−2 determined by an outdoor 3 E n e rg y (e V ) 4 1 .0 3 .5 2 .5 h e a te d d e E (2 B (3 C (4 0 .8 A b s o rb a n c e (O D ) 3 v ic 0 n 0 n 0 n 2 1 .5 e s : m ) m ) m ) 0 .6 0 .4 0 .2 0 .0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 W a v e le n g th ( n m ) FIG. 2: Internal quantum eciency of devices B, C and E. 1 5 d e v ic e B ) 2 C u r r e n t d e n s ity ( m A /c m / C / 1 0 V o c js c F F 5 = 0 .8 6 / 0 .8 6 V = 8 .3 / 9 .2 m A /c m 2 = 0 .6 5 8 / 0 .6 2 2 ηP C E = 4 . 8 / 5 . 0 % 0 -5 -1 0 -0 .5 0 -0 .2 5 0 .0 0 0 .2 5 0 .5 0 0 .7 5 1 .0 0 V o lt a g e ( V ) FIG. 3: Current-voltage characteristics of devices B and C in outdoor measurement. Perfomance parameters are given in the inset. Intensity is determined by an outdoor reference cell. reference cell (Fraunhofer Institute for Solar Energy Systems, Freiburg, Germany). In Fig. 3 the corresponding current-voltage curves are presented. Temperature of the assembly platform was 32.8 ◦ C. Nevertheless, a higher temperature of the devices during the measurement has to be expected. We estimate the device temperature to be around 45 ◦ C since the device could not be cooled directly. By this reason a higher ll factor and a lower open circuit 4 voltage are observed as compared to the reported measurements under sun simulator. However, PCEs of 4.8 % and 5.0 % are determined for device B and C, respectively. Thus, the reported eciencies for these devices are conrmed. III. OPTICAL MODEL To separate the absorption of active absorber layers from absorption within transport layers and metal contact, we use a transfer-matrix-formalism to model the device optically [1]. Values of the optical constants n and k were derived by tting transmission and reection spectra of thin lm layers of the respective materials [2]. However, the accuracy of these values is limited, in that they do not account for the eect of dopant admixture into Di-NPD and C60 . Optical constants of BPAPF were measured with dopant, although a thin neat layer of BPAPF is also used in the device. The mixed layer optical constants were determined on a heated quartz glas substrate. That means, we can not account for the inuence of the C60 underlayer or a possible spatially-dependence of the mixed layer optical constants with this method. In Fig. 4 the calculated absorption prole of devices B, C, and D are presented to show that the thinlm optics of device B and C is optimized for maximum absorption in the mixed active layers. IV. [1] E. Centurioni. Applied Optics REFERENCES , 44(35):75327539, 2005. [2] T. Fritz, J. Hahn, and H. Boettcher. , 170(2):249257, 1989. Thin Solid Films 5 s im u la te d a b s o r p tio n p r o file s o f d e v ic e s B , C , E 2 .5 ) 3 0 .0 h · 1 ( 1 x f l u a b 0 .5 s o r b 1 .0 e d 0 2 1 .5 C p B 8 o / s m t o 2 .0 E n - in c o m in g lig h t T ) : C 6 0 4 0 0 2 5 5 0 7 5 m ( n 6 1 0 0 i x m 2 0 d 6 C 0 C D - C l A n V 0 6 3 0 1 2 5 x - s ta c k p o s itio n ( n m ) FIG. 4: Absorbed photon ux within device B, C and E as calculated by optical modelling. In device B and C, the absorption prole exhibits a maximum in the mixed layer showing that the choosen transport layer thickness is optimal for maximized absorption. In device E the maximum is not reached, meaning that a slightly higher hole transport layer thickness would be needed for optimized absorption.