1. Angle of incidence effects on the energy conversion behavior of polycrystalline silicon photovoltaic cells. R.J. Beal 1, B.G. Potter, Jr. 1,2 and J.H. Simmons 1,2,3 1 Materials Science and Engineering, 2 Optical Sciences, University of Arizona, Tucson, AZ 85721 3 Florida Gulf Coast University, Ft. Myers, FL 33965 Introduction and Motivation  Accurate prediction of solar power production is critical to effective grid integration.  The energy conversion efficiency of fielded photovoltaic systems is dependent upon cell design, installation and environmentally mediated factors contributing to module response. ConclusionsAcknowledgements Experimental Details  ML Solar polycrystalline Si cells (SiN x AR coating, cell thickness = 250  m) Specimen size - 2.5cm x 5cm Bare cells and cells with encapsulant overlayer laminate (ethylene-vinyl acetate (EVA)/Na-Ca silicate glass) to provide optical consistency with typical module structure. Incident-angle-dependent EQE:  Commercial EQE measurement system (PV Measurements, Inc.) modified to provide angle- dependent measurement Collimated, tunable, spectral source Coupled rotation of electronic contacts and cell. Isolation of geometric (Lambert cosine law) and optical effects intrinsic to materials and cell construction via integrated shadow mask  Empirically defined parameter sets are often used to model total integrated irradiance to electrical energy transduction, including the impact of local variation in irradiance and environmental conditions, to predict cell irradiance-to- power (ITP) behavior.  Nonempirical, physics-based models would provide an opportunity to predict module behavior under arbitrary optical and environmental conditions.  GOAL: evaluate a nonempirical, intrinsic spectral response function (EQE) that could be integrated into established ITP models for improved PV power conversion prediction. Results: EQE( ,, specimen configuration)  Short circuit current (i.e. indicator of cell energy conversion efficiency) computed assuming AM1.5 irradiance spectrum and experimentally determined EQE(  results.  No mask data (blue diamonds) isolates  -related optical phenomena associated with material/cell architecture.  Enhancement of 3-4% in J sc over normal incidence value observed in encapsulated cells. Associated with increased incoherent scattering within laminate structure (multiple interfaces, volumetric scattering) – increased irradiance at PV junction.  Masked measurement - cosine law reduction in irradiance at the cell results in significant reduction in EQE values and associated J sc.  No mask - the cosine related effects on irradiance are suppressed, isolating incidence angle effects now associated with the intrinsic materials and design of the cell.  Bare cell exhibits increased EQE variability with wavelength that is enhanced with increased . Contrasts that observed with encapsulated cell structure, showing more “flat” EQE dispersion from 500 – 800 nm.  Consistent with specular reflectance data showing increased reflectivity dispersion in bare cell.  Physically derived, cell-specific spectral response functions (EQE(  )) are identified as a potential refinement over empirical parameters sets used in standard ITP models that can enhance module output prediction under arbitrary irradiance and incidence conditions for a given cell/module design.  The novel integration of a removable mask into EQE measurement allows the examination of intrinsic, angle- dependent variability in cell/module response associated with materials of construction and architecture, free from extrinsic, cosine effects on irradiance.  New opportunity for direct, experimental validation of enhanced light management strategies for emerging third generation PV technologies. External Quantum Efficiency (EQE) Specimens  Sample configuration and measurement conditions shown with encapsulant overlayer at arbitrary incidence angle (  ).  With mask Mask maintains consistent illumination area on cell. Projected area of illumination (i.e. irradiance magnitude) scales with cos(  ) (Lambert cosine law).  No mask Projected area of illumination constant. Lambert cosine effect offset by cos(  )-scaled increase in illuminated area of cell with  increase. Lambert Cosine Law:  ( , ) =  0 (0, ) cos (  ) J sc ( ,, specimen configuration) Cosine law observed with  change Cosine law not exhibited with  change EQE system with modified optical path and stage Masked No Mask Reflectance  This material is based upon work supported by the Department of Energy/EERE under DE-EE0006017. The authors also thank C. Hansen (Sandia National Laboratories) for informative and insightful discussions. Representative PV cells tested, with (right) and without (left) encapulsant layers