Research On Conjugated Polymer-based Organic Solar Cells

The utilization of renewable solar energy is one of the main approaches toovercome the present energy crisis. Solar cell (also photovoltaic device) is an electronicdevice which can convert light into electricity. Due to the complicated fabricationprocess and high cost of silicon solar cell, this environmental friendly technology hasnot been widely used currently. Compared with silicon solar cells, polymer-basedorganic photovoltaic (OPV) systems hold the promise for a cost-effective, lightweightsolar energy conversion platform, which could benefit from simple solution processingof the active layer.We reviewed the typical device structures and principle of polymer solar cells inthis thesis. The morphology and interface of the device based on poly(3-hexylthiophene)(P3HT) and fullerene derivative have been explored. In addition, several as-synthesizedpolymers have been characterized for OPV application.High-boiling solvent1,2,4-trichlorobenzene (TCB) was used as solvent to dissolveP3HT and fullerene derivative composites in regular structure to enhance the deviceperformance. We found that the degree of P3HT chain ordering was improved due to theultra-slow evaporating velocity of TCB, which resulted in improved light absorptionand carrier mobility of the composite film. The devices based on active layers cast fromTCB achieved higher efficiencies compared with those of the reference ones.Zinc oxide (ZnO) film fabricated from precursor doped with triethylene glycolmonomethyl ether (TGME) showed improved film quality. The as-prepared ZnO filmacted the buffer layer for electron collection. The addition of TGME into the precursorled to various work functions and wettability of the ZnO film, which resulted indramatically enhanced device performance. The inverted P3HT:PCBM device based onZnO precursor doped with TGME achieved a power conversion efficiency (PCE) ashigh as4.7%due to optimizing the interface control.The photovoltaic behavior of four new conjugated polymers as donor materials hasbeen investigated. We confirmed that deep highest occupied molecular orbital (HOMO) level of donor could lead to an improved open-circuit voltage (Voc). In addition, thedonor/acceptor weight ratio played a critical role on the performance of device.However,1,8-diiodooctane (DIO) showed an ambiguous effect on the newpolymer-based organic solar cells. A PCE of4.02%and a high Vocof0.94V have beenachieved in poly{6,6’-di(2-ethylhexyl)isoindigo-alt-2,6’-4,8-di(2,3-dihexylthienyl)benzo[1,2-b:4,5-b’]dithiophene}(PID-DTBDT) polymer-based devices. Also excellentPCE of4.24%and a Vocof0.71V have been achieved in poly{2,5-bis-(2-ethylhexyl)-2,5-dihydro-pyrrolo[3,4-]pyrrole-1,4-dione-alt-2,6’-4,8-di(2,3-dihexylthienyl)benzo[1,2-b:4,5-b’]dithiophene (PDPP-DTBDT) polymer-based devices.