Freeform micro-optical arrays (FMOAs) can overcome some limitations of rotationally symmetric optical components. The manufacturability assessment for FMOA designs containing many freeform elements is demanding. We present computer-aided design (CAD) tools that analyze FMOA designs for manufacturing constraints. They 1) extract the height (Sag) and 2) local slope while highlighting areas beyond manufacturing limits, 3) extract the minimum tool radius and 4) convert CADs into ray traceable solids using NURBS for performance comparison of the actual micro-structure to the design. Critical parameters can be identified early, reducing time-consuming and costly adjustments later.

The need for free-form micro-optics (FFMO) is constantly growing in well-established business segments including flatpanel displays, solid-state illumination, thin-film solutions for security/anti-counterfeiting applications, AR/VR wearables, and automotive headlights. However, the high access barriers to pre-commercial production capabilities prevent companies, especially SMEs, from exploiting the FFMO technology in commercial products and hinder further innovation. To lower the barrier to access FMOA technology, CSEM and their partners have established the PHABULOuS Pilot Line. PHABULOuS offers a unique one-stop shop for all requests for prototyping and manufacturing of free-form microoptics services, from pilot to full-scale production. To mature the FMOA technology, the Pilot Line members have developed high precision origination techniques complemented by industry-fit, high-throughput up-scaling technologies for the cost-effective production of large-area FFMO. At the core of these technologies is Step & Repeat UV imprinting. The method has been successfully demonstrated in the PHABULOuS project for high precision upscaling of rigid small masters to flexible tools with 600 x 300 mm2 dimensions using a standard UV-NIL stepper modified for this purpose. Since there is currently no commercial Step & Repeat machine on the market able to replicate free-form micro-structures on large area with the required precision, CSEM has developed a high precision S&R UV-replication platform designed specifically to this purpose. Combined with the expertise in design and optical simulation, origination, and electroforming, the newly developed Step&Repeat capabilities at CSEM will strengthen the PHABULOuS Pilot Line offerings.

Photonics integration continues to be a main driver for innovation in multiple aspects, including wafer-scale integration, new materials, sub-micron alignment of components and protection from harsh environment. We show cost-effective fabrication technologies of micro-optical components by UV wafer-scale replication into chemically stable polymers. Furthermore, for simplified fiber coupling and packaging, a novel 90° optical interconnect is presented, integrated with self-alignment structures. Replicated, space compliant microlenses on packaged CMOS imagers show improved light sensitivity by a factor 1.8. A laser based, low stress bonding process is explored to generate wafer-scale hermetic enclosures for harsh environment applications ranging from space to implants.

Sheet resistance losses and local defects are challenges faced in solar module fabrication and upscaling processes. Commonly used investigation tools are non-invasive optical and thermal imaging techniques, such as electroluminescence, photoluminescence as well as illuminated and dark infrared imaging. Here, we investigate the potential of computationally efficient finite element simulation of solar cells and modules by considering planar electrodes coupled by a local current–voltage coupling law. Sheet resistances are determined by fitting current simulation results of an OPV solar cell to electroluminescence imaging data. Moreover, a thermal model is introduced that accounts for Joule heating due to an electrothermal coupling. A direct comparison of simulated temperature maps to measured infrared images is therefore possible. The electrothermal model is successfully validated by comparing measured and simulated temperature profiles across four interconnected organic solar cells of a mini-module. Furthermore, the influence of shunts on the thermal behavior of OPV modules is investigated by comparing electrothermal simulation results to dark lock-In IR thermography images.

Solution processable organic tandem solar cells offer a promising approach to achieve cost-effective, lightweight and flexible photovoltaics. In order to further enhance the efficiency of optimized organic tandem cells, diffractive light-management nanostructures were designed for an optimal redistribution of the light as function of both wavelength and propagation angles in both sub-cells. As the fabrication of these optical structures is compatible with roll-to-roll production techniques such as hot-embossing or UV NIL imprinting, they present an optimal cost-effective solution for printed photovoltaics. Tandem cells with power conversion efficiencies of 8-10% were fabricated in the ambient atmosphere by doctor blade coating, selected to approximate the conditions during roll-to-roll manufacturing. Application of the light management structure onto an 8.7% efficient encapsulated tandem cell boosted the conversion efficiency of the cell to 9.5%.

Printed photovoltaics promise lightweight and flexible light harvesting devices for conformal integration into buildings, portable electronics or vehicles. This is enabled by employing thin photoactive layers, which can reduce the use of sometimes costly and scarce absorber materials. Since this in turn comes along with an incomplete light absorption and hence restrains the power conversion efficiency of printed photovoltaics, their development was since long accompanied by integrated light management. However, besides a mere efficiency enhancement, new strategies should consider both functionality and additional costs of the light management. Optical enhancement strategies should consequently avoid complications with the delicate printing of the photovoltaic layers and therefore structures on the light incident surface of the device have been proposed. However, these air-faced approaches are prone to the impacts and stress of operating conditions and hence a protected solution is desired. Here we introduce a carefully designed photonic nanostructure embedded in a self-contained transparent film, which offers a conformal device attachment. An efficiency enhancement of 11% is demonstrated on an organic photovoltaic device. Angle dependent measurements moreover suggest a yearly increase of 13%, exploiting the seasonal asymmetry of the incident solar power by a built-in asymmetric diffraction.

A simple lamination process of the top electrode for perovskite solar cells is demonstrated. The laminate electrode consists of a transparent and conductive plastic/metal mesh substrate, coated with an adhesive mixture of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS, and sorbitol. The laminate electrode showed a high degree of transparency of 85%. Best cell performance was achieved for laminate electrodes prepared with a sorbitol concentration of ~30 wt% per milliliter PEDOT:PSS dispersion, and using a pre-annealing temperature of 120°C for 10 min before lamination. Thereby, perovskite solar cells with stabilized power conversion efficiencies of (7.6 ± 1.0)% were obtained which corresponds to 80% of the reference devices with reflective opaque gold electrodes.

We present in-coupling gratings for improving the performance of thin film organic solar cells. The impact of the grating on the absorption in the active layer is modeled and explained using a standard cell architecture. An increase in absorption of 14.8% is predicted and is shown to be independent from the active material. The structure is then applied on blade-coated devices and yields an efficiency improvement of 12%. The angular behavior of the structures is measured showing superior performance for two dimensional gratings. By simulating the current generation for different angles and illumination conditions, we predict a total yearly increase of the generated current of 12% using an optimized grating. The fabrication of these structures, moreover, is compatible with roll-to-roll production techniques, thus making them an optimal solution for printed photovoltaics.

In standard unencapsulated poly(3‐hexylthiophene):[6,6]‐phenyl C61‐butyric acid methyl ester solar cells exposed to humid air, the oxidation of the aluminum cathode is known to be a key degradation mechanism. Water that enters the device at the edges and through pinholes diffuses to the organic–electrode interface. The forming oxide acts as a thin insulating layer that gives rise to an injection/extraction barrier and leads to a loss in the device current. In order to understand this behavior in detail various steady‐state, transient, and impedance measurement techniques are performed in combination with drift‐diffusion simulations. With this combinatorial approach the dominant degradation mechanism is confirmed to be the development of a blocking interface layer. This layer grows laterally leading to a loss in effective area due to the rapid local oxidation of the aluminum layer. Thus by combining multiple electrical techniques and optoelectrical simulations the dominant degradation mechanism can be evaluated. The same methodology is also beneficial for more stable and efficient novel solar cells.

Accurate characterization and reporting of organic photovoltaic (OPV) device performance remains one of the important challenges in the field. The large spread among the efficiencies of devices with the same structure reported by different groups is significantly caused by different procedures and equipment used during testing. The presented article addresses this issue by offering a new method of device testing using “suitcase sample” approach combined with outdoor testing that limits the diversity of the equipment, and a strict measurement protocol. A round robin outdoor characterization of roll-to-roll coated OPV cells and modules conducted among 46 laboratories worldwide is presented, where the samples and the testing equipment were integrated in a compact suitcase that served both as a sample transportation tool and as a holder and test equipment during testing. In addition, an internet based coordination was used via plasticphotovoltaics.org that allowed fast and efficient communication among participants and provided a controlled reporting format for the results that eased the analysis of the data. The reported deviations among the laboratories were limited to 5% when compared to the Si reference device integrated in the suitcase and were up to 8% when calculated using the local irradiance data. Therefore, this method offers a fast, cheap and efficient tool for sample sharing and testing that allows conducting outdoor measurements of OPV devices in a reproducible manner.

The long-term (up to 100 days) stabilities of thin films of a trimethine cyanine dye (Cy3-P) and of Cy3-P/C60 bilayer solar cells with initial power conversion efficiencies of up to 3.6% in the regular and inverted device architecture were studied. For storage conditions under nitrogen at room temperature in the dark, Cy3-P films were stable and no decrease in performance was measured for inverted ITO/TiO2/C60/Cy3-P/MoO3/Ag solar cells. ITO/PEDOT:PSS and aluminum were found to be responsible for a slight inherent degradation of regular solar cells under inert storage conditions. Solar cells stressed at accelerated (80°C) full sun simulation showed a burn-in period of ~5 days with a performance loss of 75%. This initial performance decrease might be linked to the photopolymerization reaction of C60. For longer times, performances stabilized and arrived at 15% of the initial values after a test period of 17 days.

Polymer blends of MDMO-PPV with three different electron accepting cyano-substituted polymers have been investigated with photoinduced absorption (PIA) spectroscopy. In these blends, an efficient photoinduced charge transfer occurs that quenches the photoluminescence and produces a significant photovoltaic effect when the blends are incorporated as active layer into a solar cell configuration. Surprisingly, PIA spectroscopy in the millisecond time domain reveals that in the blends neutral triplet photoexcitations are almost exclusively formed in favor of polaronic charge carriers with yields higher than in the individual polymers. In the blends, the triplet state resides on the component with the lowest optical bandgap. The enhanced triplet generation is rationalized by the recombination of photogenerated charge carriers into a triplet state. This process may occur when the energy of the charge-separated state is higher than that of the triplet state. We demonstrate that this process is likely to occur in polymer solar cells with a high open-circuit voltage.

Near-steady-state photoinduced absorption (PIA) spectroscopy is employed to study the charge carrier dynamics in polymer:fullerene (poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1-4-phenylene vinylene]: 1-(3-methoxycarbonyl)-propyl-1-phenyl-[6,6]C61; MDMO-PPV:PCBM) solar cells under operating conditions. Artifacts in the PIA spectra originating from thermal heating of the aluminum electrode and from interference of incoming and reflected light waves are analyzed. PIA signals from functioning devices are studied as a function of applied bias and temperature and complemented with photocurrent measurements under identical conditions. Comparison between photocurrent and PIA measurements shows that PIA mainly probes trapped cationic charge carriers while the photocurrent samples mobile carriers. The number density of trap sites is estimated at 1017cm−3 and trapped carriers can be stabilized by applying a reverse bias potential over the device.

The recombination of photogenerated charge carriers in poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene]:1-(3-methoxycarbonyl)-propyl-1-phenyl-[6,6]C61 bulk-heterojunction solar cells is investigated using the time delayed collection field technique. Here the lifetime of photogenerated electrons and holes that have escaped charge recombination can be determined from current measurements using a pulsed collection voltage that is delayed with respect to the excitation pulse. At 80K, the number of long lived charge carriers decays in time according to t−α with α=0.2, practically independent of laser fluence in the range of 1–1000μJ∕cm2. For excitation density <4μJ∕cm2 the number of long lived carriers (nL) depends linearly on the fluence. At higher fluence, nL is limited by a process that occurs in the time span between generation and carrier extraction under a constant bias (−4V). Continuous background illumination reduces the lifetime of long lived carriers, probably by filling the low energy trap sites, for which a number density of 1017cm−3 is estimated. Recombination of long lived carriers at 80K in the 1–1000μs range is not limited by the (bimolecular) rate of nongeminate electron and hole encounter. Instead, the rate is limited by a monomolecular process, which may be the detrapping of one type of carrier or the recombination within a Coulombically bound electron-hole pair.

The influence of a periodically modulated electric field on the concentration of photogenerated charges in bulk-heterojunction solar cells of poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-[6,6]C61 (PCBM) is studied at 80K by near-steady-state photoinduced absorption (PIA) spectroscopy. Measurements are complemented with recording the photocurrent. The results show that the lifetime of extractable charge carriers under conditions where the built-in electrical field is largely compensated, is in the sub-millisecond time domain. PIA is dominated by the contribution from trapped carriers and application of a −4V bias increases the number of trap sites available to the carriers in comparison with a +1V bias voltage. The reverse bias voltage also leads to an enhancement in the generation rate of carriers that can be trapped and/or the lifetime of the trapped carriers. The experiment indicates that the lifetime of the trapped carriers at −4V bias voltage remains in the sub-millisecond time domain.

The photophysical properties of a solution processed blend of two semiconducting polymers with electron donating and electron accepting properties, respectively, as used in polymer photovoltaic devices have been investigated. We show that in the binary mixture of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) and poly[oxa-1,4-phenylene-(1-cyano-1,2-vinylene)-(2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylene)-1,2-(2-cyanovinylene)-1,4-phenylene] (PCNEPV) photoexcitation of either one of the polymers results in formation of a luminescent exciplex at the interface of the two materials. Photoinduced absorption spectroscopy shows that this exciplex can decay to the lowest triplet state (T-1) of MDMO-PPV. Application of an electric field results in dissociation of the marginally stable exciplex into charge carriers, which provides the basis for the photovoltaic effect of this combination of materials. Spin allowed recombination of the charge carriers to the MDMO-PPV T-1 state is invoked to explain the field-enhanced quantum yield for triplet formation observed by photoinduced reflection measurements on photovoltaic devices made from the composite films. The field enhanced triplet yield is identified as loss mechanism for the photovoltaic performance of this combination of materials.