Research Of Polymer/Quantum Dots Hybrid Solar Cells

Since Alivisatos et al. demonstrated polymer/nanocrystals(NCs) solar cells for the first time, hybrid photovoltaic devices have attracted considerable attentions by using NCs as an electron acceptor to replace the conventional fullerene derivatives which usually exhibit weak absorbance in the visible region. In this thesis,we studied the polymer/PbX hybrid solar cells and its performance.For the Planar Heterojunction Hybrid Solar Cells system, a series of polymers was used to form the polymer/PbSe planar heterojunction hybrid solar cells. The device performance shows a great improvement compared to the pure quantum dots solar cells and the Voc almost keep in constant enhancement for a series of polymers as their highest occupied molecular orbital(HOMO) levels lay above the valence band(VB) of PbSe QDs. A polymer interfacial dipole was demonstrated to increase Voc due to increased built-in potential to decrease interfacial resistance. The photovoltage can be up to 0.66 V and the best device performance shows a power conversion efficiency(PCE) of 5.31% based on the poly(2,6-(N-(1-octylnonyl) dithieno[3,2-b:20,30-d]pyrrole)-alt-4,7-(2,1,3-benzothiadiazole))(PDTPBT)/PbSe system. Better device performance can be obtained as the improved hole transport properties evidenced by the high PL quenching efficiency. In addition, the QDs layers upon the polymer layer show different morphologies as the different molecular polarity of the polymers, which results in the variation of the PCE for different polymer/PbSe systems.For the Polymer/Polymer:PbSe/PbSe P-I-N Heterojunction Hybrid Solar Cell system. HSCs employing a low band-gap polymer and PbSxSe1-x alloy NCs have been demonstrated. A record-high PCE of 5.50% and a maximum FF of 67% were achieved for such type of HSCs. The remarkable device efficiency can partially be attributed to the excellent photovoltaic properties of the PbSxSe1-x NCs which show improved performance than either the conventional PbS or PbSe NCs. Furthermore, we thoroughly investigated the evolution of the three-dimensional morphology of the polymer/NCs blend by changing the polymer:NCs ratio and confirmed the forming of vertical phase segregation with an upper NCs-rich region and a polymer-rich region beneath. After depositing one more layer of NCs on top of the blend film, a desired device architecture with the vertical D-D:A-A structure was obtained, which facilitates charge separation and transport, leading to greatly improved device performance.