Efficiency Rise in PCDTBT:PC70BM Organic Solar Cell

Efficiency Rise in PCDTBTPC70BM constitutive(a) solar CellEfficiency Rise in PCDTBTPC70BM Organic Solar Cell Using Interface AdditiveRashmi Swami, Rajesh Awasthi, Sanjay TiwariAbstractSolar cell can be designed with photo mobile layer of total and inorganic actuals. Organic materials, specially polymers, argon a promising alternative to traditional semiconductors as the active material for solar cell because of their low cost, low temperature energy bear on, low material requirement, can be used on flexible substrate, can be shaped to suit architectural application. Low efficiency is one of the biggest problem with organic solar cell. In order to increase the efficiency of bulk hetero-junction organic solar cell we are using interface surfactant analogue poly(oxyethylene tridecyl ether) (PTE) with amalgamate photoactive layer. Here we are reporting on the enhanced photovoltaic (PV) effects by means of a polymer bulk-hetero-junction (BHJ) layer having PCDTBT which is poly(N-9-h eptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)) as a low-band gap e donor/HTL polymer and PC70BM which is 6,6-phenyl C70 butyric acid methyl ester as an acceptor/ETL, doped with poly(oxyethylene tridecyl ether) (PTE) which is an interface surfactant additive. For PCDTBTPC70BM organic solar cell , we put down 0.886 V open-circuit voltage (VOC), 11.7 mA/cm2 short-circuit current density (JSC), and 47.3% fill factor (FF) and PCE of 4.9%. For PCDTBTPCBM70PTE organic solar cell, we recorded VOC of 0.904 V, higher values of JSC of 13.8 mA/cm2, FF of 48.2% and improved PCE of 6.0% for a PTE concentration of ca. 0.164 wt%. advocator innovation efficiency (PCE) reaches to 6.0%, by the addition of PTE to a PCDTBTPC70BM system which is much higher than a fictional character gimmick not including the additive (4.9%). Increase in efficiency is because of the increase in lifetime of missionary station carrier, which is due to the existence of PTE molecules at the interfaces sandwiched between the BHJ photovoltaic active layer and the anode and cathode, in addition to the phase-separated BHJ domains interfaces.Keywords Organic Solar Cell, PCDTBT, PCBM, PTE, IPCE, Bulk hetero-junction.IntroductionThe global rising demand for low-priced electricity has triggered deep research on solar cells comprising organic semiconductors. Organic solar cell (OSC) technology has received significant attention over the past decade due to the simple, flexible nature of polymer photovoltaics and the potential to develop a clean, cost-efficient renewable energy source. The key development of organic solar cells has been made with the pioneering concept of bulk hetero-junction (BHJ) photoactive layers 1-2.The bulk hetero-junction (BHJ) PSC 13 is of particular interest, due to the efficient photo-induced generation of charge in its unify photovoltaic (PV) layer, that is consisted of interpenetrating, channel-like domains of separated fullerene and polymer. Foll owing the annealing of the BHJ structure at elevated temperatures, PSCs with PV layers of P3HT which is poly(3-hexylthiophene) and PCBM60 which is phenyl C61-butyric acid methyl ester have shown high power conversion efficiencies (PCEs) of 3-5%. Efficiency of P3HTPCBM organic solar cell is upto 5% because of the regulateations of conventional P3HT, whose bandgap lies at around 1.9 eV, which limits absorbance to wavelengths below 650 nm 4. To improve the efficiency of PSC we need new active materials having lower bandgap to harvest more solar photons. More recently, a PCE of 5-6% was reported for a BHJ PSC that used a blend of PCBM70 and PCDTBT having a bandgap of 1.88 eV 5,6. Using processing additives PCE of organic solar cell can be increased 7-9. To increase carrier lifetimes (reduce recombination loss) we modify the BHJ interfaces between the phase-separated domains of the donor-conjugated polymer and the acceptor fullerene, and added a non-ionic surfactant poly(oxyethylene tri decyl ether) (PTE) as an additive to the PV layer. In this paper we investigated J-V characteristic and IPCE spectra of PCDTBTPC70BM organic solar cell with and without PTE.1.1 Donor moleculeNext generation HTL/donor material for organic photovoltaics is Poly9-(1-octylnonyl)-9H-carbazole-2.7-diyl-2.5-thiophenediyl-2.1.3 benzothiadiazole-4.7-diyl-2.5-thiophenediyl (PCDTBT) shown in Fig. (1) which can declare better efficiencies and lifetimes. The main qualities of PCDTBT are lower HOMO and LUMO levelsnarrow band gapIncreased open circuit voltageLonger wavelength absorption trim back concentration and material usageImproved stability under ambient conditionsHigh electron and hole generation rate and high mobility of electron and hole.Fig. 1. molecular(a) structure of PCDTBT.1.2 Acceptor moleculeExtremely symmetrical cage-shaped molecules of carbon atoms is Fullerenes as shown in Fig. (2). For the separation of photoexcited exciton into free charge carriers blending of conjugated poly mers (electron donor) with fullerenes (electron acceptors), is extremely efficient way.Fig. 2. molecular(a) structure of PC70BM.1.3 PTE additivePoly(oxyethylene tridecyl ether) (PTE) shown in Fig. (3) as an additive have low (- 8.1 eV) highest- occupied-molecular-orbital (HOMO) and high (2.1 eV) lowest-unoccupied-molecular- orbital (LUMO) 1012.Fig. 3. Molecular structure of PTE.Experimental DetailsThe sample BHJ PSCs were sham in a sandwich structure with an anode of indium tin oxide (ITO) and an AlLi/Al cathode. Patterned 80-nm-thick ITO glass was cleaned by sequential ultrasonic give-and-take in detergent, deionized water, acetone, and isopropanol, and then treated in an ultraviolet-ozone chamber for 15 min. Then, a ca. 40-nm-thick hole-collecting PEDOTPSS buffer layer was spin-coated onto the ITO electrode. On the top of the PEDOTPSS layer spin coat the blended solution of PCDTBT (0.456 wt%), PCBM70 (1.824 wt%), and PTE additive in dichlorobenzene. The PV layer was about 85 nm thick. Finally, for the cathode, a ca. 1-nmthick AlLi alloy (Li 0.1 wt%) layer and a pure Al (ca. 50-nm-thick) layer were created on the photovoliaic layer through thermal deposition (0.5 nm/s), at a foundation pressure below 210-4 Pa. The sample device structure studied was therefore ITO/PEDOTPSS/PCDTBTPC70BMPTE/AlLi/Al as shown in Fig. (4). The active area of the fabricated device was 33 mm2. For comparison, a reference PSC was fabricated with the structure ITO/PEDOTPSS/PCDTBTPC70BM/AlLi/Al as shown in Fig. (5). In snow mW/cm2 illumination intensity produced by an AM 1.5G light resource, the performance of the PSCs was measured,. With the inspection and repair of a source meter (Keithley 2400) the photocurrent-versus-voltage (J-V) characteristics were measured. The IPCE (incident photon-to-current collection efficiency) spectrum were measured for the PSCs studied using an IPCE measurement system.Fig. 4. ITO/PEDOTPSS/ PCDTBTPC70BMPTE /AlLi/Al Organic Solar Cell.Fig. 5. ITO/PEDOTP SS/ PCDTBTPC70BM /AlLi/Al Organic Solar Cell.Results And DiscussionAs shown in Fig. (6) for PCDTBTPC70BM organic solar cell , under an illumination of AM 1.5G and 100 mW/cm2, we recorded 0.886 V open-circuit voltage (VOC), 11.7 mA/cm2 short-circuit current density (JSC) and 47.3% of fill factor (FF) and PCE of 4.9% a value comparable with those reported by others 6. For PCDTBTPC70BMPTE organic solar cell, we recorded VOC of 0.904 V, higher values of JSC of 13.8 mA/cm2, FF of 48.2% and improved PCE of 6.0% for a PTE concentration of ca. 0.164 wt%. These increased values resulted in an improved efficiency of 6.0%, which led to a PCE that was up to 22% higher than that of PCDTBTPC70BM based organic solar cell.Fig. 6. The current-voltage characteristics of BHJ OSCs with and without the PTE additive.We further investigated the PV performance of the OSCs that incorporated the PTE additive by studying the IPCE spectra. Fig. (7) shows the observed IPCE spectrum of the PSC devices. It can be seen that the IPCE values are consistent with the variations in JSC for the OSCs with and without the PTE additive. The maximum IPCE was 73.0% at 470 nm for the sample device with the PTE additive, which corresponded to the highest JSC (13.8 mA/cm2 ), while the IPCE value was about 60.9% for the reference device without the additive, which had the lowest JSC (11.7 mA/cm2 ).Fig. 7. IPCE spectra of PCDTBTPC70 BM OSCs with and without the PTE additive.ConclusionsIn conclusion, we have reported on the use of a low-bandgap PCDTBTPC70BM-based PV layer that incorporates a PTE surfactant, which was used to the BHJ interfaces in OSCs. We have shown that BHJ OSCs that contain the interface PTE additive are more efficient than conventional OSCs. A high PCE (6.0%) was obtained for our PCDTBTPC70BM (14 w/w) OSC device using 0.164 wt% of the PTE additive, which yielded improvements in PCE of up to 22%. This improvement may be attributed to the increased selective flow of dissociated charge carr iers, not only at the interfaces of the PV layer and the electrodes, but also at the BHJ interfaces between the PCDTBT and PC70BM domains. Our findings show that a combination of PTE interface additives and high-performance low-band gap PV materials holds great potential for the development of a new generation of highly efficient OSCs.References1 G. Yu, J. Gao, J.C. Hummelen, F. Wudl, A.J. Heeger. Polymer Photovoltaic CellsEnhanced Efficiencies via a Network of Internal Donor-Acceptor Heterojunctions. Science, New Series, 1995, 270(5243) 1789-1791.2 J.J.M. Halls, C.A. Walsh, N.C. Greenham, E.A. Marseglia, R.H. Friend, S.C. Moratti, A.B. Holmes. Efficient photodiodes from interpenetrating polymer networks. Nature, 1995, 376 498500.3 C. J. Brabec, N. S. Sariciftci, and J. C. Hummelen. Plastic solar cells. Adv. Funct. Mater. 2001, 11(1) 1526.4 K. M. Coakley and M. D. McGehee. 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