Spectroscopic Signature of Trap States in Assembled CdSe Nanocrystal Hybrid Films

View at Publisher| Export | Download | More... Journal of Physical Chemistry C Volume 116, Issue 30, 2 August 2012, Pages 16259-16263 Spectroscopic signature of trap states in assembled cdse nanocrystal hybrid films (Article) Virgili, T.a , López, I.S.a, Vercelli, B.cd, Angella, G.cd, Zotti, G.cd, Cabanillas-Gonzalez, J.e, Granados, D.e, Luer, L.e, Wannemacher, R.e, Tassone, F.b a Istituto di Fotonica e Nanotecnologie (IFN) CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza L. Da Vinci 32, 20133 Milano, Italy b CNST, IIT, Via Pascoli 70, 20133 Milano, Italy c IENI, CNR, Corso Stati Uniti 4, 35127 Padova, Italy d Via Cozzi 53, 20125 Milano, Italy e Instituto Madrileño de Estudios Avanzados (IMDEA-Nanociencia), Cantoblanco, 28049 Madrid, Spain Hide additional affiliations View references (42) Abstract We report on femtosecond to millisecond pump-probe experiments performed on a multilayered structure composed by the alternation of CdSe nanocrystals (NCs) and poly(p-styrenesulphonic acid) (PSSH). We found that, after a few picoseconds of pumping at high intensity, an intense photoinduced absorption band and a strong derivative feature emerge in the differential absorption spectrum, both overlapping with the positive bleaching bands of the filled exciton states. These two former spectral features are long-living well into the millisecond range, and we attribute them to the population of charged trap states, located close to the NC surface, and thus inducing a Stark effect through the strong electric field they generate inside the NC.