Fill Factor Analysis of Organic Solar Cell

gourmandize Factor Analysis of Organic Solar CellRashmi Swami, Rajesh Awasthi, Sanjay Tiwari knock offSolar cadre is a device utilize to convert get down into electricity. It commode be made by perfect and in constituent(a) materials. Its near important parameters are expand dress circle voltage, short rope authoritative, engross agentive role and conversion efficiency. This paper is based on the analysis of divisors that incite the aim constituent of natural solar cell using MATLAB. scarf out factor is calculated using conventional organic solar cell pretence without series and shunt resistances and immutable light generated online for dickens different mouldings first using Exponential pitch-black attribute and atomic number 16 using Polynomial dark characteristic. We get for exponential agency V-I relationship improver in ideality factor n, will reduce the occupy factor and for multinomial V-I relationship increase in m will increase suffice fact or. A large dependance of light generated authentic Iph on increase applied voltage would cause a noteworthy drop in accept factor. Increase or decrease in an redundant factor would accordingly limiting require factor. Dark current can be varied in two ways, one by alter mobility and other by varying injection barrier heights. In some(prenominal) the cases shoot factor increases proportionately with .Keywords Organic solar cell, sate factor, ideality factor, open duty tour voltage, HTL, ETL.IntroductionBilayer organic solar cell as shown in fig. 1(a) is a device in which thin layer of organic material (donor and acceptor) is used between electrodes to convert light into electricity. This work is completely based on bilayer structure of organic solar cell as shown in fig.1(a) in which poly(9,9-dioctylfluorene-co-bis-N,N-(4-butylphenyl)-bis-N,N-phenyl-1,4phenylenediamine) (PFB) is organic donor/HTL and poly(9,9-dioctylfluorene-co-benzothiadiazole) ( F8BT) is organic acc eptor/ETL. Fig. 1(b) shows simplest conventional organic solar cell model without series and shunt resistances. Open circuit voltage, short circuit current, gorge factor and efficiency are four important parameters of OSC.FF = Vmax Imax / VOC ISCWhen Vm= VOC and Im= ISC whitherfore (FF)max=1.For a good photo-voltaic device, all three factors FF, VOC, ISC should be large so that it can deliver large output situation for the same sequential optical power.(b)Fig. 1 (a) Bilayer organic solar cell structure. (b) Conventional organic solar cell model without series and shunt resistances.Simulation manikin and Analysis of Fill FactorTwo cases lease been studied, one where dark characteristic is exponential like p-n junction and other where dark characteristics is polynomial like in space charge limited devices.1.2.1Exponential Current voltage Relationship In this model, dark characteristic is assumed to follow exponential current voltage relationship and Iph is assumed to be cons tant. (1)where n is ideality factor and Vth is thermal voltage, Iph is light generated current, Id is dark current and I is net output current.Total output dance stepd current can be pen as a agency of photo-generated current and dark current.(2)Output power of organic solar cell when it is operating at voltage V and giving current I-If maximum power is obtained at voltage Vm, , here assuming (3)Here y exp(y) is Lamberts W mold (4)and (5)At VOC net output current will be zero. At this agree eq. (2) will give(6)1.2.2 Polynomial Current-Voltage RelationshipIn this case it is assumed that dark current depends on the applied voltage in the following manner- (7)Where K is constant and . (8)If photovoltaic is operated at voltage V and output current is I, output power will be-To calculate choose factor, one needs to find out the maximum power which photo-voltaic cell can supply. If maximum power is delivered at voltage VmThis will give, (9)and (10)At VOC net output current will be zero. At this condition eq. (8) will give (11)and (12)1.2.3 Effect of Dark Current on Fill Factor Simulation using 1D drift-diffusion electrical modeling of bilayer OSC in MATLAB is done. We obtained that the dependence of light generated current on the applied voltage means that fill factor would depend on it as well besides make up of dark characteristics. An estimate of variation of light current can be obtained by taking dimension of its value at short circuit and open circuit condition At 0 volt, At VOC, i.e. The ratio is a measure of how drop in Iph with the voltage. This ratio can be written as Thus shows an additional factor that would affect fill factor. As this factor increases or decreases, the fill factor should accordingly change too.Results and ConclusionsEq. (3) suggests that as ideality factor n is changed, keeping reverse saturation current I0 and photo-generated current Iph constant, Vm changes in much(prenominal) a manner that (Vm/n) remains constant. So Im will also be constant as it is a function of (Vm/n). From eq. (6) open circuit voltage is also changes with ideality factor n such that (VOC/n) remains constant. It follows from the above reasoning that (Im/ISC) and (Vm/VOC) will be unchanged if n will vary keeping the reverse saturation current constant. indeed as ideality factor n varies keeping the reverse saturation current I0 constant, fill factor of the device will remain unchanged. Though if open circuit voltage (VOC) assumed to be constant by varying reverse saturation current I0 as ideality factor n changes, fill factor will change accordingly.Assuming Iph to be 1 mA-cm-2, I0 to be mA-cm-2 and ideality factor n to be 1, open circuit voltage and fill factor come out to be 1.25 volts and 0.9 respectively. Taking Iph and VOC constant, the variation of fill factor with ideality factor n is shown in fig. 2. We get that increase in the value of ideality factor n, will reduce the value of fill factorFig. 2 form of fill fact or with ideality constant n. open circuit voltage and light generated current are taken to be constant as 1.25 V and 1 mA-cm-2 respectively.Eq. (12) shows that fill factor is a function of m. Variation of fill factor with m is shown in fig. 3. For m = 1, FF = 0.25. As m increases fill factor also increases and approaches to 1. However, FF will become notwithstanding 1 when m is infinity. In this case also, m is a measure of the sharpness of the characteristic curve. As m increases, I-V curve becomes increasingly sharper resulting in a high fill factor. For polynomial dark characteristic with constant light generated current we get that increase in m will increase fill factor which approaches to 1Fig. 3 Variation of fill factor with m. fill factor approaches to 1 as m becomes larger and larger.Simulation results revealed in fig. 4 show that light generated current Iph is a function of applied voltage, means FF would depend on it as well besides shape of dark characteristic. A larg e dependence of Iph on increasing applied voltage would cause a significant drop in FF. Increase or decrease in an additional factor would accordingly change fill factor. Dark current can be varied in two ways, one by varying mobility and other by varying injection barrier heights. In both the cases fill factor increases proportionately with as shown in fig. 5 and fig. 6.Fig. 4 Dependence of light generated current on the applied voltage. and are the sea dog and electron mobilities respectively. and are the injection barriers at anode and cathode respectively.Fig. 5 Variation of fill factor with for 0.1eV and 0.3eV injection barrier heights. Different points have been obtained by ever-changing mobility.Fig. 6 Variation of fill factor with for carrier mobilities and . Different points have been obtained by changing injection barrier height.ReferencesJ. A. Barker, C. M. Ramsdale, and N. C. Greenham, Modeling the current-voltage characteristics of bilayer polymer photovolt aic devices, carnal Review B 67, (2003), 075205.D. P. Grubera, G. Meinhardtb and W. Papousekc, Modelling the light absorption in organic photovoltaic devices, Solar Energy Materials and Solar Cells, 87, (2005), 215-223.J. Wagner, T. Fritz, and H. Bottcher, Computer modelling of organic thin film solar cells exciton model of photocurrent generation, Physica Status Solidi A, 136, (1993), 423.Y. Roichman and N. Tessler, Generalized wizardry relation for disordered semiconductors implications for device performance, Appl. Phys. Lett., 80, (2002), 1948.J. C. Scott and G. G. Malliaras, Charge injection and recombination at the metal-organic interface, Chem. Phys. Lett., 299, (1999), 115.S. E. Shaheen, C. J. Brabec, N. S. Sariciftci, F. Padinger, T. Fromherz, and J. C. Hummelen, 2.5 % efficient organic plastic solar cells, Appl. Phys. Lett., 78, (2001), 841-843B. K. Crone, P. S. Davids, I. H. Cambell and D. L. Smith, Device model investigation of bilayer organic light emitting doide, J. Appl. Phys., 84, (2000), 1974.P. W. M. Blom, M. J. M. de Jong and S. Breedijk, Temperature dependent electron hole recombination in polymer light emitting diodes, Appl. Phys. Lett., 71, (1997), 930.C. M. Ramsdale, J. A. Barker, A. C. Arias, J. D. MacKenzie, R. H. Friend and N. C. Greenham, The origin of open circuit voltage in polyfluorene-based photovoltaic device, J. Appl. Phys, 92, (2002),4266.B. Mazhari, An improved solar cell circuit model for organic solar cells, Solar Energy Materials Solar Cells, 90, (2002), 1021.