Glass/glass (G/G) photovoltaic modules are quickly rising in popularity, but the durability of modern G/G packaging has not yet been established. In this work, we examine the interfacial degradation modes in G/G and glass/transparent backsheet modules under damp heat (DH) with and without system bias voltage, comparing emerging polyolefin elastomer (POE) and industry-standard poly(ethylene-co-vinyl acetate) (EVA) encapsulants. We investigate the transport of ionic species at cell/encapsulant interfaces, demonstrating that POE limits both sodium and silver ion migration compared with EVA. Changes to the chemical structures of the encapsulants at the cell/encapsulant interfaces demonstrate that both POE and EVA are more susceptible to degradation in modules with a transparent backsheet than in the G/G configuration. Adhesion testing reveals that POE and EVA have comparable critical debond energies after the DH exposures regardless of system bias polarity. The results of this study indicate that the interfacial degradation mechanisms of G/G appear to be similar to those of conventional glass/backsheet modules. For emerging materials, our results demonstrate that POE offers advantages over EVA but that transparent backsheets may accelerate encapsulant degradation due to increased moisture ingress when compared with the G/G structure.

Photovoltaic modules at the mm-scale are demonstrated in this work to power wirelessly interconnected mm-scale sensor systems operating under low flux conditions, enabling applications in the Internet of Things and biological sensors. Module efficiency is found to be limited by perimeter recombination for individual cells, and shunt leakage for the series-connected module configuration. We utilize GaAs and AlGaAs junction barrier isolation between interconnected cells to dramatically reduce shunt leakage current. A photovoltaic module with eight series-connected cells and total area of 1.27-mm demonstrates a power conversion efficiency of greater than 26 % under low-flux near infrared illumination (850 nm at 1 μW/mm). The output voltage of the module is greater than 5 V, providing a voltage up-conversion efficiency of more than 90 %. We demonstrate direct photovoltaic charging of a 16 μAh pair of thin-film lithium-ion batteries under dim light conditions, enabling the perpetual operation of practical mm-scale wirelessly interconnected systems.

While Germany has led the market in photovoltaic (PV) implementation throughout the last decade, there has been increasing criticism of PV support policies due to their high cost. Although declining, the levelized cost of electricity (LCOE) from PV is still above the German wholesale electricity price. However, using LCOE as an evaluation yardstick falls short in at least 2 respects: It neither takes into account integration costs rising with PV penetration (ie, undervaluing its actual cost) nor avoided externalities of replacing conventional for renewable generation (social cost overvaluation). We thus calculate the social profitability of PV in Germany by including not only private costs and benefits but also integration costs to the electricity system and avoided environmental externalities, using the internal rate of return and the profitability index as indicators. Our results show that when these factors are considered, the social profitability of PV in Germany is higher than 10% at the lower bound of the social cost of carbon (150€/tCO) up to a penetration level of at least 15% and positive up to a penetration level of at least 25%. Results also show the level of private profitability if all externalities were internalized and assert that subsidies are justified to align private and social profitability. The proposed method could be used as a complementary indicator to private profitability by public institutions, development banks, and companies with social responsibility values.

We present a universally applicable 3D-printed external light trap for enhanced absorption in solar cells. The macroscopic external light trap is placed at the sun-facing surface of the solar cell and retro-reflects the light that would otherwise escape. The light trap consists of a reflective parabolic concentrator placed on top of a reflective cage. Upon placement of the light trap, an improvement of 15% of both the photocurrent and the power conversion efficiency in a thin-film nanocrystalline silicon (nc-Si:H) solar cell is measured. The trapped light traverses the solar cell several times within the reflective cage thereby increasing the total absorption in the cell. Consequently, the trap reduces optical losses and enhances the absorption over the entire spectrum. The components of the light trap are 3D printed and made of smoothened, silver-coated thermoplastic. In contrast to conventional light trapping methods, external light trapping leaves the material quality and the electrical properties of the solar cell unaffected. To explain the theoretical operation of the external light trap, we introduce a model that predicts the absorption enhancement in the solar cell by the external light trap. The corresponding calculated path length enhancement shows good agreement with the empirically derived value from the opto-electrical data of the solar cell. Moreover, we analyze the influence of the angle of incidence on the parasitic absorptance to obtain full understanding of the trap performance. © 2015 The Authors. published by John Wiley & Sons, Ltd.

Herein, we present a prototype of a photovoltaic module that combines a luminescent solar concentrator integrating one-dimensional photonic crystals and in-plane CuInGaSe (CIGS) solar cells. Highly uniform and wide-area nanostructured multilayers with photonic crystal properties were deposited by a cost-efficient and scalable liquid processing amenable to large-scale fabrication. Their role is to both maximize light absorption in the targeted spectral range, determined by the fluorophore employed, and minimize losses caused by emission at angles within the escape cone of the planar concentrator. From a structural perspective, the porous nature of the layers facilitates the integration with the thermoplastic polymers typically used to encapsulate and seal these modules. Judicious design of the module geometry, as well as of the optical properties of the dielectric mirrors employed, allows optimizing light guiding and hence photovoltaic performance while preserving a great deal of transparency. Optimized in-plane designs like the one herein proposed are of relevance for building integrated photovoltaics, as ease of fabrication, long-term stability and improved performance are simultaneously achieved. © 2015 The Authors. published by John Wiley & Sons Ltd.

Reducing absorber layer thickness below 500 nm in regular Cu(In,Ga)Se (CIGS) solar cells decreases cell efficiency considerably, as both short-circuit current and open-circuit voltage are reduced because of incomplete absorption and high Mo/CIGS rear interface recombination. In this work, an innovative rear cell design is developed to avoid both effects: a highly reflective rear surface passivation layer with nano-sized local point contact openings is employed to enhance rear internal reflection and decrease the rear surface recombination velocity significantly, as compared with a standard Mo/CIGS rear interface. The formation of nano-sphere shaped precipitates in chemical bath deposition of CdS is used to generate nano-sized point contact openings. Evaporation of MgF coated with a thin atomic layer deposited AlO layer, or direct current magnetron sputtering of AlO are used as rear surface passivation layers. Rear internal reflection is enhanced substantially by the increased thickness of the passivation layer, and also the rear surface recombination velocity is reduced at the AlO/CIGS rear interface. (MgF/)AlO rear surface passivated ultra-thin CIGS solar cells are fabricated, showing an increase in short circuit current and open circuit voltage compared to unpassivated reference cells with equivalent CIGS thickness. Accordingly, average solar cell efficiencies of 13.5% are realized for 385 nm thick CIGS absorber layers, compared with 9.1% efficiency for the corresponding unpassivated reference cells.

A novel method, , is found to show significant enhancement of the short circuit current (35%) when applied as a scattering back reflector for polycrystalline silicon thin-film solar cells. The coating is formed from high refractive index titania particles without containing binder and gives close to 100% reflectance for wavelengths above 400 nm. Snow globe coating is a physicochemical coating method executable in pH neutral media. The mild conditions of this process make this method applicable to many different types of solar cells.

The polycrystalline CdS/CdTe thin-film solar cell in the superstrate configuration has been studied by spectroscopic ellipsometry (SE) using glass side illumination whereby the reflection from the glass/film-stack interface is collected whereas that from the ambient/glass interface is rejected. The SE data analysis applies dielectric functions ( ) for solar cell component materials obtained by variable-angle and in-situ SE. In the SE analysis of the complete cell, a step-wise procedure ranks the free parameters, including thicknesses and those defining the spectra in , according to their ability to reduce the root-mean-square deviation between simulated and measured SE spectra, and the best-fit results compare well with electron microscopy. Combining all SE results, the solar cell quantum efficiency (QE) can be simulated without free parameters, and comparisons with QE measurements enable identification of losses. The capabilities have wide applications in photovoltaic module mapping and in-line monitoring.