Sai-Wing Tsang

Morphology control in polycarbazole based bulk heterojunction solar cells and its impact on device performance

Incremental increase in dimethyl sulfoxide (or dimethyl formamide) in ortho-dichlorobenzene solution of poly[N-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) gradually reduces the polymer-solvent interaction, the attraction forces between polymer chains become more dominant, and the polymer chains adopt a tight and contracted conformation with more interchain interactions, resulting in a progressive aggregation in both solutions and films. This was used to fine tune the morphology of PCDTBT/PC71BM based solar cells, leading to improved domain structure and hole mobility in the active layer, and significantly improved photovoltaic performance. The power conversion efficiency increased from 6.0% to 7.1% on devices with an active area of 1.0u2002cm2.

Highly efficient cross-linked PbS nanocrystal/C60 hybrid heterojunction photovoltaic cells

We present a highly efficient hybrid heterojunction photovoltaic (PV) cell with a colloidal inorganic nanocrystal (NC) electron donor and an organic electron acceptor. The heterojunction is formed by a thin film of cross-linked PbS NCs and a C60 layer. Compared to the PbS-only PV cell, the heterojunction device has improved the power conversion efficient (PCE) from 1.6 % to 2.2 %. The C60 layer effectively prevents the excitons from quenching at the NC/metal interface, which is demonstrated with a significant improvement of the fill-factor (FF) of the heterojunction devices. In addition, a larger open-circuit voltage (VOC) in the heterojunction devices suggests that the electrons in C60 can readily transfer to the PbS NCs through the NC surface linkers. This is supported by the measured optical absorption spectrum of the hybrid system.

Self-organized phase segregation between inorganic nanocrystals and PC61BM for hybrid high-efficiency bulk heterojunction photovoltaic cells

We demonstrate a simple approach to generate phase segregation between colloidal PbS nanocrystals (NCs) and organic [6,6]-phenyl C61 butyric acid methyl ester (PC61BM). Continuous vertical phase segregation is observed in cross-linked composite films of NCs and PC61BM. Hybrid bulk heterojunction photovoltaic cells fabricated with the phase segreated composite layer have achieved the state-of-art power conversion efficiency of 3.7% under one sun of simulated Air Mass 1.5 Global solar irradiation. The presented method can be generally applied in other NC/organic systems for the development of hybrid heterojunction photovoltaic cells.

Impact of interfacial dipole on carrier transport in bulk heterojunction poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester blends

The electron transport properties in various poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) blend films, prepared by various process conditions, were investigated by admittance spectroscopy at different temperatures. It was found that the electron mobility and the dispersive transport behavior showed a strong dependence on the thermal treatment condition; the blend with the fastest growth rate had orders of magnitude reduction in the mobility and a much more dispersive transport. Using the Gaussian disorder model, it was found that the energetic disorder of the density-of-states between blends plays a significant role in the observed phenomena. It is proposed that the difference in the energetic disorder is due to the interfacial dipole effect at the P3HT/PC61BM heterojunctions in the various blend films.

Erratum: Development of a new benzo(1,2-b:4,5-b′)dithiophene-based copolymer with conjugated dithienylbenzothiadiazolevinylene side chains for efficient solar cells (Chemical Communications (2011) (9381-9383) (DOI: 10.1039/c1cc12851e))

Although the work published in this paper proved reproducible by at least three different researchers in the St. Andrews laboratories, it could not be reproduced elsewhere, nor could it be reproduced in St. Andrews when we changed to a different batch of 1,1,1-tris(diphenylphosphinomethyl)ethane (triphos). Subsequent study has now produced a protocol which is reproducible not only in our hands but also in the laboratories of Professor Walter Leitner and Dr. Jürgen Klankermeyer at RWTH, Aachen. Full details of the new procedure will be published elsewhere, but we report below an example for the hydrogenation of acetanilide as carried out in St. Andrews and Aachen.

Highly efficient cross-linked PbS nanocrystal/C 60 hybrid heterojunction photovoltaic cell

We present a highly efficient hybrid heterojunction photovoltaic (PV) cell with a colloidal inorganic nanocrystal (NC) electron donor and an organic electron acceptor. The heterojunction is formed by a thin film of cross-linked PbS NCs and a C 60 layer. Compared to the PbS-only PV cell, the heterojunction device has improved the power conversion efficient (PCE) from 1.6 % to 2.2 %. The C 60 layer effectively prevents the excitons from quenching at the NC/metal interface, which is demonstrated with a significant improvement of the fill-factor (FF) of the heterojunction devices. In addition, a larger open-circuit voltage (V OC ) in the heterojunction devices suggests that the electrons in C 60 can readily transfer to the PbS NCs through the NC surface linkers. This is supported by the measured optical absorption spectrum of the hybrid system.