Organic photovoltaic (OPV) devices have shown remarkable performance progress in recent years, reaching current record power conversion efficiency (PCE) values of 16.4% for single junction and 17.3% for multi junction devices, owing mostly to the impressive developments made within synthesis of new non-fullerene acceptors. This progress places organic solar cells at the forefront of thin-film photovoltaic technology. However, in order to meet industrial demands and reach high performance values in industrial settings, further research and development efforts within Roll-to-Roll (R2R) and Sheet-to-Sheet (S2S) processing of OPV devices under ambient conditions are required. Furthermore, OPV modules being manufactured through such up-scaled processing techniques should ideally be developed from low cost materials, and show good stability towards various different operational stress conditions. In this work, we demonstrate combined R2R and S2S development of ITO-free OPV devices, which are based on the non-fullerene material system PBDB-T:ITIC. The 2 devices are processed from R2R vacuum sputtering and S2S slot-die coating at ambient conditions, and reach cell PCE values of 5.5%. In addition, we introduce a correlation between different barrier films, both commercial and sputtered inorganic coatings on ultra-clean PET, and the lifetime of the developed devices. The results therefore demonstrate an important step in the development of OPV devices from R2R and S2S processes in industrial settings.

The light activation phenomenon in inverted P3HT:PCBM bulk heterojunction organic solar cells based on titanium oxide sublayer (TiOx) is characterized by fast acquisition of current-voltage (J-V) curves under light bias as function of time. TiOx layers were thermally treated under inert atmosphere at different temperatures prior active layer deposition and for every device an activation time was extracted. It is shown that the higher the TiOx annealing temperature, the faster the activation. The improvement of the overall device performances is also observed for devices with TiOx layers baked above 100 °C. The evolution of the characteristic of the organic semiconductors (OSC) device, from dielectric to diode, is attributed to the increase of TiOx conductivity by three orders of magnitude upon white light illumination. Additionally, devices based on baked TiOx present higher conductivity than those based on unbaked TiOx which would explain the gain in performances and the short activation time of the OSC. In order to understand the origin of the phenomenon, deactivation experiments were also performed under different conditions on OSC. The deactivation process was shown to be thermally dependent and fully reversible under inert atmosphere, which suggest that deep traps are responsible for the activation phenomenon. An optimal annealing temperature was found at 120 °C and gives a reasonable short activation time of approximately 1 min and photo conversion efficiency up to 4%.

Upconversion of sunlight with energy below the band gap of a solar cell is a promising technique for enhancing the cell efficiency, simply by utilizing a larger part of the solar spectrum. The present topical review addresses this concept and discusses the material properties needed for an efficient upconversion process with focus on both silicon and organic solar cells. To design efficient upconverters, insight into topics such as quantum-optics, nano-optics, numerical modeling, optimization, material fabrication, and material characterization is paramount, and the necessary concepts are introduced throughout the review. Upconversion modeling is done using rate equations, while optical modeling is done by solving Maxwell's equations using the finite element method. Topology optimization is introduced and used to generate geometries of gold nanoparticles capable of greatly enhancing the upconversion yield. Fabrication and experimental characterization methods are discussed. Some recent results are presented and finally the possibility of designing upconverting materials capable of increasing the short-circuit current in a solar cell is discussed.

Organic photovoltaic solar cells are a promising option for cheap, renewable energy, but must improve in their stability.

The development of nonfullerene acceptors (NFAs) has led to dramatic improvements in the device efficiencies of organic photovoltaic (OPV) cells. To date it is, however, still unclear how those laboratory‐scale efficiencies transfer to commercial modules, and how stable these devices will be when processed via industrially compatible methods. Herein, the degradation behavior of lab‐scale and scalable OPV devices using similar nonfullerene‐based active layers is assessed. It is demonstrated that the scalable NFA OPV exhibits completely reversible degradation when assessed in ISOS‐O‐1 outdoor conditions, which is in contrast to the laboratory‐scale devices assessed via the indoor ISOS‐L‐2 protocol. Results from transient photovoltage (TPV) indicate the presence of charge trap formation, and a number of potential mechanisms are proposed for the selective occurrence of this in laboratory‐scale devices tested in ISOS‐L laboratory conditions—ultimately concluding that it has its origins in the different device architectures used. The study points at the risk of assessing active layer stability from laboratory‐scale devices and degradation studies alone and highlights the importance of using a diverse range of testing conditions and ISOS protocols for such assessment.

PSS, ZnO sol-gel, and ZnO nanoparticles. PV performances are found to be low when the ZnO nanoparticles layer is used. This performance loss is attributed to the formation of many dewetting points in the active layer, because of a relatively high roughness of the ZnO nanoparticles layer, compared to the other layers. We successfully circumvented this phenomenon by adding a small quantity of polystyrene (PS) in the active layer. The introduction of PS improves the quality of film forming and reduces the dark currents of solar cells. Using this method, high-efficiency devices were achieved, even in the case of substrates with higher roughness.

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We compare pristine and degraded samples that were subjected to outdoor degradation following standard ISOS-O2 protocol. The ideality factors for different incident wavelengths obtained from open circuit voltage versus irradiation level and current density-voltage (J-V) measurements at different temperatures, indicate that for aged samples recombination is governed by Shockley-Red-Hall mechanism occurring in a region near the anode. Samples were also characterized using impedance spectroscopy and fitted to an electrical model. Impedance parameters were used to obtain mobility, indicating a clear degradation of the active layer blend for aged samples. The change in the chemical capacitance also reveals a worsening in carrier extraction. Finally, 2D numerical simulations and fits to experimental J-V curves confirm the existence of a layer near the anode contact with poorer mobility and a decrease of the anode work function for the degraded samples.