Polymers cells are the next-generation class of photovoltaic since they promise realization of light weights, mechanically flexible, larger area devices. The room temperature solution processing can be used in fabricating these devices. High-efficiency conversion power of about 10% has recently been obtained in tandem polymer cells (Huo et al., 2015). In single-junction, it’s achievable through lowering the density state to a level lower than the electron acceptor and the conduction band of the semi-conductor. Photovoltage is electromotive force obtained by a photosensitive material due to inducing radiant energy; photovoltaic relates electric current produced at a junction of two materials when subjected to light. Fill factor is the maximum power derived from a solar cell in ratio with the product of Voc and Isc.
Tandem are still the most efficient than single-junction polymer cells (PSCs) due to their relative overlap between the absorption and the solar spectrum. The efficiency of the ( PSCs) is limited by low open-circuit(Voc) differentiating lowest uncopied molecular orbital (LUMO) of the acceptor with the highest occupied molecular orbital of the donor. Dissociation leading to free carriers of charge result to the reduction of (Voc) described by other factors such as apparent dependence, illumination intensity varying acceptor or donor fraction and formation of the transfer of ground state charge states between fullerene and polymer. Recent research also indicates that (DOS) density states for the (LUMO) acceptor and donor (HUMO) and energy disorder may have importance functional significance in resulting Voc.
In demonstrating key open-circuit voltage losses of ( PSVs) indicates that decrease in band trailing and increase split of electrons (Huo et al., 2015). The levels of holes quasi-Fermi are responsible for increase of (Voc) and narrow –band gap is used so as to improve PCE of PSCs towards 10%.
Fluorine substituents method represents a promising electron donor due to its preserved PTB7 level and HOMO -The evidence by photovoltaic characteristics and photo response to the devices. The experiment indicates that fluorine method is an efficient and successful strategy to increase Voc by deepening LUMU levels thereby enhancing photocurrent when it lowers bandgap of the polymer (Huo et al., 2015).Further enhancement of Voc and the overall PTB7-Th devices performance is in the parameters design – a big impact is in the composition. Characteristics of J-V, when plotted, produce a series of curves; experiment obtains measured indicates monotonic increase mainly due to improved mobility of electrons contrast earlier observation, therefore, conclusion that the main limiting factors in the device are not exciton, dissociation, and charge generation.
The characteristics of Dark J-V devices are dependence of Voc intensity of light. Investigation of Voc at dark current saturation is negligible further recombination on PC¬71BM content proof is weak dependence. When measured under dark and illumination shows exponential curves with identical gradients, and hence, finding are consistent with the previous observations and conclusions that decreasing in donor-acceptors band trailing of materials resulting into in split of electrons and quasi-Fermi holes at specific density is giving the open circuit voltage in PSCs.
Conclusion
The single junction is highly efficient PSCs having PCEs of over 10% represent a positive move towards achieving of economical solar cells. These materials can be obtained from narrow synthesized bandgap semiconducting polymers consisting a control of a trailed density lower than acceptor conductor band coupled with deep HOMO. Therefore, shortly interest should be directly directed towards fully exploiting the new polymer elecytron donors by using a load of PC71BM in the blend.
References
He, Z., Xiao, B., Liu, F., Wu, H., Yang, Y., & Xiao, S. et al. (2015). Single-junction polymer solar cells with high efficiency and photovoltage. he blend and should lead to the advance of other polymer material to achieve high efficiency.
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Huo, L., Liu, T., Sun, X., Cai, Y., Heeger, A., & Sun, Y. (2015). Single-Junction Organic Solar Cells Based on a Novel Wide-Bandgap Polymer with Efficiency of 9.7%. Adv. Mater., 27(18), 2938-2944. http://dx.doi.org/10.1002/adma.201500647
Hänni, S., Bugnon, G., Parascandolo, G., Boccard, M., Escarré, J., & Despeisse, M. et al. (2013). High-efficiency microcrystalline silicon single-junction solar cells. Prog. Photovolt: Res. Appl., n/a-n/a. http://dx.doi.org/10.1002/pip.2398
Chen, J., Cui, C., Li, Y., Zhou, L., Ou, Q., & Li, C. et al. (2015). Polymer Solar Cells: Single-Junction Polymer Solar Cells Exceeding 10% Power Conversion Efficiency (Adv. Mater. 6/2015). Adv. Mater., 27(6), 1132-1132. http://dx.doi.org/10.1002/adma.201570040
