Organic Photovoltaic-approaching High Performance Of Polymer Solar Cells And Near-infrared Photodetectors

Polymer photovoltaics, polymer solar cells (PSCs) and polymer photodetectors (PPDs)have received great attention from both academic and industrial sectors as they are flexibleand have large scale production potential and low-cost grid power generation. However, bothPSCs and PPDs are still inferior to their inorganic counterparts in efficiency and stability. Inorder to advance large-scale commercialization and implementation, their performance mustbe improved. In this dissertation, we focus on improving the performance of PSCs and PPDs.The performance of PSCs by employing the―donor-acceptor‖conjugated polymer(PBDT-DTNT) with an electron withdrawing group, naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole(NT), as the electron donor polymer. By controlling the nanomorphology of the bulkheterojunction (BHJ) composite films through thermal annealing and solvent additive, theoptimized performance of the PSCs was observed. These results indicate that the polymerPBDT-DTNT is a promising electron donor material. We further fabricated inverted PSCs byusing an alcohol soluble and thermal-crosslinkable conjugated polymer PFN-OX, as theelectron extraction layer (EEL) and PBDT-DTNT blended with fullerene derivatives as BHJcomposite. It was found that an efficiency of8.62%is observed from the inverted PSCs withBHJ film thickness of280nm. Remarkably, an efficiency of7.20%is observed from theinverted PSCs with BHJ film thickness over1000nm. Such high efficiency from such thickBHJ composite film is attributed to the high hole mobility of PBDT-DTNT from BHJcomposite, which are characterized by the space-charge-limited-current method, andgrazing-incidence small-angle and wide-angle x-ray scattering measurement. The highefficiency from the inverted PSCs with such thick BHJ composite film certainly provides asolution to resolve the bottleneck problem for manufacturing PSCs products by low-cost highthroughput roll-to-roll processing.In the third part of this dissertation, near-infrared (NIR) PPDs was fabricated andcharacterized. Operating at room temperature, the PPDs exhibited spectral response from400to1100nm, with detectivity greater than1013cm Hz1/2/W at wavelength from400to950nmand greater than1010cm Hz1/2/W from950to1100nm. It was found that the PPDs with PFNinterlayer show a better diode characteristic than that without PFN interlayer. At the reverse bias, the dark current of the PPDs with PFN interlayer was considerably suppressed, resultingin a reduced dark current, consequently high detectivity. These results demonstrated that theNIR PPDs are comparable to Si-based PDs.In the fourth part of this dissertation, we further investigated the performance of PPDswith an inverted device structure. An alcohol soluble and thermal-crosslinkable conjugatedpolymer PFN-OX used as the EEL to construct the inverted PPDs. The PPDs with ZnO as theEEL was also fabricated for comparative study. Operating at room temperature, theresponsivity of the PPDs with the PFN-OX interlayer reaches116mA/W, and possesses acorresponding detectivity of1.02×1013cm Hz1/2/W at the wavelength of800nm, which arenearly one order of magnitude higher than those with ZnO as the EEL. Our results offeranother approach to fabricate high sensitivity inverted NIR PPDs.