In recent years semiconductor nanocrystal or quantum-dot-based solar cells have drawn signiﬁcant attention as viable candidates for boosting the energy conversion eﬃciency beyond the traditional Shockley and Queisser limit of 32% for Si-based solar cells.
Because of the extremely small size of semiconductor quantum dots and high absorption cross section, it is possible to capture nearly all of the incident solar light in the visible region with an extremely thin layer of semiconductor materials. These heterojunction semiconductor solar cells, often referred as ETA (extremely thin absorber) cells, oﬀer new opportunities to develop relatively inexpensive solar cells.
A transformative approach is required to meet the demand of economically viable solar cell technology. By making use of recent advances in semiconductor nanocrystal research, scientifics of Notre Dame University have now developed a one-coat solar paint for designing quantum dot solar cells. A binder-free paste consisting of CdS, CdSe, and TiO2 semiconductor nanoparticles was prepared, they adopted two synthetic strategies: (1) physical mixing of commercially available TiO2 (Degussa P25) and bulk CdS (Aldrich) in a mixed solvent (water and t-butanol); (2) a pseudoSILAR (sequential ionic layer adsorption and reaction) method of depositing CdS (or CdSe) on suspended TiO2 nanoparticles by the addition of Cd2+ and S2-(or Se2) in a stepwise fashion; and the resulting thick, yellow paste of TiO2 and CdS could then be applied directly on conducting glass electrodes at 473 K. The photoconversion behavior of these semiconductor ﬁlm electrodes was evaluated in a photoelectrochemical cell consisting of grapheneCu2S counter electrode and sulﬁde/polysulﬁde redox couple. Open-circuit voltage as high as 600 mV and short circuit current of 3.1 mA/cm2 were obtained with CdS/TiO2CdSe/TiO2 electrodes. A power conversion eﬃciency exceeding 1% has been obtained for solar cells constructed using the simple conventional paint brush approach under ambient conditions.
Whereas further improvements are necessary to develop strategies for large area, all solid state devices, this initial eﬀort to prepare solar paint oﬀers the advantages of simple design and economically viable next generation solar cells.
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Matthew P. Genovese, Ian V. Lightcap, and Prashant V. Kamat
ACS Nano 2012 6 (1), 865-872