Photocarrier Dynamics in Polymer Bulk Heterojunction Solar Cells
Date Issued
2011
Date
2011
Author(s)
Li, Shao-Sian
Abstract
In this thesis, photocarrier dynamics in bulk heterojunction polymer solar cell was comprehensively investigated with various transient techniques. Power conversion efficiency of polymer solar cells have been remarkably improved by the optimization of donor/acceptor blending nanomorphologies, which are vital for efficient photocurrent generation. It also significantly affects the phtotocarrier dynamics such as exciton dissociation, carrier mobility and transport recombination. This thesis not only aims to correlate carrier dynamics and solar cell performance by morphology control but also providing a promising methodology for the future study of improvement in power conversion efficiency.
In chapter 3, TiO2 concentration dependent carrier dynamics was investigated in P3HT/TiO2 nanorods hybrid BHJ PVs. The best power conversion efficiency was found at 50wt% of TiO2 nanorods where the amount of TiO2 are enough to create a bi-continuous transport phase and resulted in balanced electron and hole mobility and also a longest carrier lifetime. Further in chapter 4, we investigated the interplay of 3-D morphologies by STEM-HAADF and the photocarrier dynamics of P3HT/TiO2 NPs and NRs hybrids BHJ PVs. The anisotropic TiO2 nanorods can not only reduce the probability of the inter-particle hopping transport of electrons by providing better connectivity with respect to the TiO2 nanoparticles, but also tend to form a large-scale donor-acceptor phase-separated morphology. The presence of dimensionality of TiO2 nanocrystals ensures the formation of favorable morphology for polymer/inorganic hybrid solar cells and results in more effective mobile carrier generation and more efficient and balanced transport of carriers.
Furthermore, in chapter 5, we present that through interface modification with effective molecules, the photovoltaic performance of P3HT/TiO2 NRs can be largely improved by enhancing charge separation and suppressing interface recombination rate in the polymer/inorganic hybrids. Similar process of surface modification can was also successfully demonstrated in P3HT/nanostructured ZnO hybrid solar cells.
The utilization of graphene oxide (GO) thin films as the hole transport and electron blocking layer in organic photovoltaics (OPVs) is demonstrated in chapter 6. The incorporation of GO as a hole transport layer leads to the decrease in recombination and leakage currents. Solar cell performance is comparable to devices fabricated with PEDOT:PSS as the hole transport layer. Indicating that GO could be a simple solution-processable alternative to PEDOT:PSS as the effective hole transport and electron blocking layer in OPV and light-emitting diode devices.
Subjects
polymer solar cell
carrier dynamics
carrier transport
carrier recombination
carrier lifetime
graphene oxide
SDGs
Type
thesis
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