| Summary: | 碩士 === 國立臺北科技大學 === 有機高分子研究所 === 105 === Perovskite solar cells have attracted considerable attention in the past few years due to the advantages of low production cost, high power conversion efficiency (PCE), broad absorbance in the UV-Vis range and low-temperature and solution fabrication process. In recent years, p-i-n planar heterojunction(PHJ)structure has been widely adoptedfor perovskite solar cells because of its simple procedure and low current–voltage hysteresis phenomenon.In such device, PEDOT：PSS is the most commonly used hole transport material (HTM). However,it is a strong acid, which will eventually etches the transparent ITO electrode, and exhibits three-dimensional inhomogeneity and anisotropic conductivity due to its lamellar structure, reducing the effective collection of carriers. In addition, several studies have shown that the work function (WF) of PEDOT:PSS lies between -4.9 and -5.1 eV, which ishigher than the ionization potential of CH3NH3PbI3 (~ -5.4 eV). This energy level difference would lead to energy loss at the CH3NH3PbI3/PEDOT：PSS interface, thus decreasing the built-in potential and corresponding performance of solar cells. To overcome these disadvantages, several new types of HTMs have been developed to replace PEDOT:PSS, such as metal oxides, graphene oxide and doped PEDOT：PSS. To further increase the efficiency, it is necessary to develop highly efficient HTMs that are compatible with perovskite precursor solution and low-temperature solution process.
In this study, we introduced poly(3-hexylthiophene)-based polyelectrolytes (P3HT-COOH and P3HT-COOK) as HTMto buildinverted perovskite solar cells. The HOMO of P3HT-COOH and P3HT-COOK was determined using AC-2 to be -5.13 eV and-5.14 eV, respectively. Both values are lower than the HOMO of PEDOT:PSS(-4.99 eV), which is beneficial for increasing the open-circuit voltage of solar cells. Consequently, the P3HT-COOK based device exhibited higher average PCEof 18.71 % with a Voc of 1.03 V and a Jsc of 21.41 mA/cm2, than the
PEDOT：PSS based cell which has an average PCE of 13.85% with a Voc of 0.94 V and a Jsc of 19.86 mA/cm 2. On the other hand,the P3HT-COOH based device has an average PCE of 15.77 %, which is slightly lower than that of the P3HT-COOK device but is still higher than that of the PEDOT：PSS based device.These findings clearly indicate that the P3HT-based polyelectrolyte is highly promising as the HTM of perovskite solar cells.
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