Doping and Morphological Control at the Semiconductor-Electrode Interface in Organic Solar Cells

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Institution: Pennsylvania State Univ University ParkTitle: Doping and Morphological Control at the Semiconductor-Electrode Interface in Organic Solar CellsIntellectual MeritOrganic polymer-based photovoltaic (OPV) cells are a potentially low-cost sunlight-to-electricity conversion technology with unique advantages compared to other solar cell technologies, such as flexibility, light weight, and facile processing. However, OPV devices suffer from low solar energy conversion efficiency and still face many technical challenges. For example, OPV devices suffer from resistive losses at the semiconductor-electrode interface. Building organic solar cells with ohmic contacts ? where the interface is non-rectifying with negligible resistive losses ? has the potential for improved fill factors, short-circuit currents, and perhaps higher open-circuit voltages, all of which have the potential to increase the efficiency of organic photovoltaics toward their theoretical limit of 15%. Current contact methodologies for organic photovoltaics rely on tuning the work function of the electrodes to match the transport energy levels of the electron donors and acceptors which make up the photoactive layer. In contrast, inorganic devices rely on site-specific doping of the semiconductor near the electrode interface to promote tunneling through the charge extraction barrier by reducing the barrier width. The proposed research will engineer organic semiconductor-electrode interfaces in organic solar cells, focusing specifically on developing a methodology analogous to site-specific doping in inorganic semiconductors by covalently linking macromolecular dopants at sub-monolayer coverage to electrode surfaces.The proposed research will synthesize p-type and n-type semiconducting polymers that can anchor to electrode materials. Though this approach, it is hypothesized that the electrical properties of organic semiconductors near the cathode and anode can be tuned to promote efficient charge extraction and explore the consequences of building ohmic contacts on solar cell device performance. By tuning the molecular structure of polymer dopants, the wetting behavior of organic semiconductors on electrode surfaces can be also controlled to control polymer phase aggregation and hence prevent shunt paths and promote further charge extraction. It is proposed that the localization of dopants at the electrode contacts may become a widely-applicable strategy for the minimization of losses at the semiconductor-electrode interface of organic solar cells.Broader ImpactsThe proposal education and outreach activities seek to launch a new initiative at Pennsylvania State University entitled ?Sunlight, Energy, Polymers? (Sun-E-Poly), which will serve as a nucleation point for current and future efforts in research, education, and outreach centered on OPV across campus. Undergraduate students, women, and under-represented minorities will be integrally involved in the proposed research activities through the current Penn State Soft Materials and Chemical Energy Storage and Conversion NSF Research Experiences for Undergraduates (REU) site programs.