Colloidal Quantum Dot Photovoltaics: The Effect of Polydispersity
详细信息 查看全文
- 作者：David Zhitomirsky ; Illan J. Kramer ; Andr茅 J. Labelle ; Armin Fischer ; Ratan Debnath ; Jun Pan ; Osman M. Bakr ; Edward H. Sargent
- 刊名：Nano Letters
- 出版年：2012
- 出版时间：February 8, 2012
- 年：2012
- 卷：12
- 期：2
- 页码：1007-1012
- 全文大小：329K
- 年卷期：v.12,no.2(February 8, 2012)
- ISSN：1530-6992
文摘
The size-effect tunability of colloidal quantum dots enables facile engineering of the bandgap at the time of nanoparticle synthesis. The dependence of effective bandgap on nanoparticle size also presents a challenge if the size dispersion, hence bandgap variability, is not well-controlled within a given quantum dot solid. The impact of this polydispersity is well-studied in luminescent devices as well as in unipolar electronic transport; however, the requirements on monodispersity have yet to be quantified in photovoltaics. Here we carry out a series of combined experimental and model-based studies aimed at clarifying, and quantifying, the importance of quantum dot monodispersity in photovoltaics. We successfully predict, using a simple model, the dependence of both open-circuit voltage and photoluminescence behavior on the density of small-bandgap (large-diameter) quantum dot inclusions. The model requires inclusion of trap states to explain the experimental data quantitatively. We then explore using this same experimentally tested model the implications of a broadened quantum dot population on device performance. We report that present-day colloidal quantum dot photovoltaic devices with typical inhomogeneous linewidths of 100鈥?50 meV are dominated by surface traps, and it is for this reason that they see marginal benefit from reduction in polydispersity. Upon eliminating surface traps, achieving inhomogeneous broadening of 50 meV or less will lead to device performance that sees very little deleterious impact from polydispersity.