Effect of Copper Sulfide nanocrystals in a Poly(3-hexylthiophene)/Titania solar cell
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Effect of Copper Sulfide nanocrystals in a Poly(3-hexylthiophene)/Titania solar cell Priscilla V. Quintana-Ramírez1 and M. C. Arenas2* 1 Posgrado en Ciencia e Ingeniería de Materiales, Centro de Física Aplicada y Tecnología, Avanzada (CFATA), Universidad Nacional Autónoma de México (UNAM), Boulevard Juriquilla 3001, Querétaro, Querétaro 76230, México. 2 Departamento de Ingeniería Molecular de Materiales, CFATA, UNAM, Boulevard Juriquilla 3001, Querétaro, Querétaro 76230, México. *Corresponding author: [email protected], Phone: +52- 44 22381173 ext. 132, +52 55 5623 4173 ext. 132
ABSTRACT Poly(3-hexylthiophene)/Titania (P3HT/TiO2) heterojunction has been widely studied in the field of hybrid solar cells. Usually, organic dyes shift the neat TiO2 absorption edge toward the visible range improving the conversion efficiency or/and the TiO2 surface is modified with ligands in order to increase the electron transport. On the other hand, copper sulfide, non-toxic semiconductor, has been included in bulk organic P3HT based solar cell, increasing the photocurrent density of devices. Therefore, we propose the use of copper sulfide in the hybrid TiO2/P3HT heterojunction to determine its effect in the performance of TiO2/P3HT solar cell. Copper sulfide nanocrystals (CuxS) were synthesized at 230 °C, 240 °C and 260 °C and, they were mixed with P3HT in order to form P3HT:CuxS bulk heterojunctions. Scattered grains and irregular morphology in the final topography of the reference device (P3HT/TiO2 heterojunction) were observed by AFM, while a granular morphology and a few pores like craters were observed in the devices containing P3HT:CuxS bulk heterojunctions. Chalcocite phase (Cu2S) was obtained at 230 and 240ºC and, digenite (Cu1.8S) phase at 260ºC, both copper sulfide phases are very promising for solar cells. Despite this, poor rectifications in the devices were found in the current-voltage curves of the devices containing copper sulfide nanocrystals in contrast to the P3HT/TiO2 cell (device without nanocrystals), it could be due to the current leakage or recombination process in the copper sulfide/TiO2 interface. It suggests future work in order to improve the devices. INTRODUCTION Semiconducting polymer Poly(3-hexylthiophene) (P3HT) joined to inorganic semiconductor Titania (TiO2) is the most studied heterojunction in hybrid solar cells area [1-9]. P3HT with a short band gap (Eg) of about 1.8 to 2 eV is a hole transporter and TiO2 of wide Eg (3.2 a 3.4 eV) is electron transporter in this hybrid heterojunction. Several strategies have been developed to improve the performance of these devices, among them are; sandwich structure or bulk heterojunction configurations [1-3], molecular interface modifiers in the heterojuntion [5-7] or surface modifiers over the TiO2 nanostructured [8,9]. Parameters like porosity of the TiO2 film, thickness and thermal processing of the hybrid structure, type of surface modifiers and
morphology and dimensions of the TiO2 nanostructures influenced significantly in the electrical parameters and
