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We investigate the effect of excitons on charge transport in photovoltaic materials with large exciton binding energies using Cu2O as a model system. We develop a thermodynamic model to estimate the fraction of excitons in Cu2O at quasi-equilibrium and find that over 20% of the generated population of carriers during photovoltaic operation could be excitons. Experiments show the presence of excitons...
We report cryogenic inductively coupled plasma reactive ion etching (ICPRIE) etched tapered silicon microwires are ideal light trapping structures with extremely low (1.08% between 400 nm–1100 nm under normal incidence) reflectivity. We show that these tapered microwire arrays absorb 90.12% of incident light under normal incidence in an effectively 20 μm thick silicon when embedded in a polymer and...
Cu2O is a p-type semiconductor that has demonstrated attractive photovoltaic properties, but its efficiencies have been limited by surface instability and lack of high quality thin films. In this work, plasma-assisted molecular beam epitaxy is used to precisely control film orientation and interface chemistry of Cu2O heterostructures. Thin films of Cu2O are deposited by MBE onto thin films of Pt and...
The II–IV-nitrides are an alloy series analogous to the well-characterized III-nitrides, where a Group II and Group IV element replace the Group III element. We report on the fabrication and structural and optoelectronic characterization of earth-abundant II–IV-nitrides: ZnSnxGe1−xN2. The sputtered thin-films show potential for ZnSnxGe1−xN2 to be tunable semiconductor photovoltaic absorber materials.
Cu2O is a p-type semiconductor with desirable bulk properties for photovoltaics. However, the lack of an n-type dopant and surface instability have hindered the development of a high efficiency Cu2O device. In this work, the floating zone method is used to grow high quality single crystals of Cu2O in order to controllably study the interfacial reactions between Cu2O and its heterojunction partners...
We discuss ‘full spectrum’ photovoltaic modules that leverage low-cost III-V compound semiconductor cells, efficient optics and unconventional fabrication/assembly methods, and discuss advances in photoelectrochemical water-splitting with high efficiency.
Many proposed next-generation photovoltaic devices have complicated nano- and micro-structured architectures that are designed to simultaneously optimize carrier collection and light absorption. Characterization of the electrical properties of these highly structured materials can be challenging due to the difficulty of creating electrical contacts, as well as the need to decouple the properties of...
Cu2O is a promising, earth-abundant alternative to traditional photovoltaic materials (CIGS, CdTe, etc.) because of its low cost, high availability, and straightforward processing. We report a method to fabricate Cu2O substrates with thicknesses of less than 20 microns which may be handled and processed into devices. Development of thinner Cu2O substrates is essential as extrinsic doping has been...
Zinc phosphide (Zn3P2) is a promising and earth-abundant alternative to traditional materials (e.g. CdTe, CIGS, a-Si) for thin film photovoltaics. The record solar energy conversion efficiency for Zn3P2 cells of 6% (M. Bhushan et al., Appl. Phys. Lett., 1980) used a Mg/Zn3P2 device geometry that required annealing to reach peak performance. Here we report photovoltaic device results and junction composition...
Silicon microwire arrays have recently demonstrated their potential for low cost, high efficiency photovoltaics. These high aspect ratio, radial junction wire arrays allow for the absorption of nearly all the incident sunlight while enabling efficient carrier extraction in the radial direction. One of the remaining challenges to make this technology commercially viable is scaling up of the microwire...
Zinc phosphide (Zn3P2) is a promising alternative to traditional materials (e.g. CIGS, CdTe, a-Si) for thin film photovoltaics. Open circuit voltage in Zn3P2 cells has been limited by Fermi-level pinning due to surfaces states and heterojunction interdiffusion, motivating the need to prepare interfaces that are electrically passive and chemically inert. We investigated the surface chemistry of Zn3...
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