To Improve The Efficiency Of P3HT: PCBM Solar Cell With PbSe Quantum Dots

Nowadays, colloidal quantum dots (CQDs) attract wide attention for itsproperties such as quantum size effect, emission spectra dependent on its size, and soon. Lead selenium (PbSe) is a kind of direct narrow band gap (0.28eV) semiconductormaterial. For its strong absorption in infrared wavelengths, as well as multiple excitongeneration (MEG) effect under illumination, it has been widely applied to the infraredoptoelectronics. The preparation method of CQDs is simple and easy to proceed. Onother hand, much attention has been paid to polymer solar cells for its low cost,simple preparation and good flexibility. Combining the advantages of CQDs andpolymers would further improve the efficiency of solar cells. To date, mostCQDs-based solar cells were fabricated with organic ligand passivation, in this way,to a certain extent, the charge carrier mobility will be reduced, and it does not favorthe solar cell efficiency. In this thesis, we adopted the method of treating PbSequantum dots with halogen ligands, and then, to mix it into the co-polymerP3HT:PCBM as active layer. In this way, we can improve the mobility of the activelayer. On other hand, by reasonably controlling the size of the PbSe quantum dots, aswell as making good use of the strong absorption in near-infrared region of PbSe QDs,we combined it with the advantages of polymers to prepare solar cells with highpower conversion efficiency.The following main conclusions can be drawn after a series of experiments:(1) By using the hydrothermal synthesis method, i.e. PbO acts as the source oflead and Se powder acts as the source of Se, we have successfully prepared PbSequantum dots with particle sizes between3nm and7nm. The absorption spectrumpeak lies between1400nm and1600nm. As the experimental data confirm that thequantum dot size can be changed by controlling the reaction time.(2) We chose poly(3-hexylthiophene)(P3HT) and [6,6]-phenyl-C61-butyric acidmethyl ester (PCBM)) as active layer. The PbSe quantum dots were used as theinfrared absorption material. By mixing the PbSe CQDs into P3HT:PCBM canenhance the near infrared absorbtion of the active layer. The performance of deviceITO/PEDOT:PSS/P3HT:PCBM:PbSe/Al is better than that of control device ITO/PEDOT:PSS/P3HT:PCBM/Al. The photocurrent can be improved afterpost-annealing.(3) We explored the post-annealing time and the post-annealing temperature onthe influence of the solar cells. Under the condition of the AM1.5white light, thehighest efficiency of device ITO/PEDOT:PSS/P3HT:PCBM:PbSe/Al reached to3.31%, and it has been improved by14.5%as compared with that of the controldevice.(4) By doping NH4Cl in the synthesis process, the surface of Pb2+can be coatedby Cl-. In this way, the exposure of Pb to the air can be avoided, and then the stabilityof PbSe quantum dots can be improved, as well as to further improve the deviceperformance and stability.