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Photovoltaic cells have been the world’s most rapidly growing energy source, with markets increasing at a compounded rate of above 4O% year. Amongst new technologies, organic solar cells (With conjugated polymers) enable low-temperature solution processing (with major cost advantages), high mechanical flexibility, and compatibility with low cost printing methods. The most efficient organic solar cells are based on bulk heterojunction (BHJ) photoactive layers layers composed of nanoparticules (NPs) dispersed within a polymer. Here, the polymer acts generally as the electron donor and the NPs are the acceptor phase. BHJ cells from NP/polymer composites have high internal quantum efficiencies due to (i) the short distance that excitons have to diffuse to reach the donor/acceptor interface, and (ii) the effective area of this interface. BHJ cells may include polymer films containing fullerene nanoparticles or its derivatives, or hybrid inorganic-NP/polymer composites. These hybrid solar cells are especially promising because inorganic NPs have a much broader and tunable absorption spectrum than organic-NPs. Silicon 2 nanoparticles (Si-NPs) stand as an abundant and environmentally friendly material. It also provides a good overlap between light absorption and solar spectra. Demonstrated by its established success in solar cell industry. Hybrid solar cells hosed on Si-NPs and the hole-transporting polymer P3HT have been recently demonstrated where encouraging PCE values of up to 1.1% were obtained [1]. In the HybridSolar project, we propose to develop and understand the physical and chemical properties of hybrid Si-NP/polymer composites, as well as to fabricate and test BHJ solar cells based on these hybrids as a means of accessing their technological potential. We will devote particular attention to the investigation and improvement of the Si-NP/polymer interface with regard to the charge separation efficiency. To this end, we propose a three-fold strategy: (i) develop film forming solutions and deposition methods to optimize the performance of the hybrid photoactive layers; (ii) improve the electronic coupling between the Si-NPs and polymer by means of establishing covalent bonds between the NPs and the polymer: (iii) reduce the density of recombination levels (detects) at the NP/polymer interface . This will be achieved through e.g. hydrogen passivation and by trap filling via phosphorous doping of the NPs. According to this strategy we will use the Si-NP/P3HT blend as a model system, since this composite has been successfully applied in BHJ solar cells. In this presentation, we will give an account of the early progress of the project., Fundação para a Ciência e a Tecnologia (FCT)

The authors thank Dr. S. Chiussi (University of Vigo) for SIMS measurements. One of the authors (S.A.F.) acknowledges Fundação para a Ciência e Tecnologia (FCT) for a post-doctorate grant., Gas-phase phosphorous and boron doping of hydrogenated nanocrystalline thin films deposited by HWCVD at a substrate temperature of 150 °C on flexible-plastic (polyethylene naphthalate, polyimide) and rigid-glass substrates is reported. The influence of the substrate, hydrogen dilution, dopant concentration and film thickness on the structural and electrical properties of the films was investigated. The dark conductivity of B- and P-doped films (σd=2.8 S/cm and 4.7 S/cm, respectively) deposited on plastic was found to be somewhat higher than that found in similar films deposited on glass. n- and p-type films with thickness below ~50 nm have values of crystalline fraction, activation energy and dark conductivity typical of doped hydrogenated amorphous silicon. This effect is observed both on glass and on plastic substrates.