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hMSCs represent a novel platform for skeletal gene therapy and the present results suggest that they can be genetically engineered to express desired therapeutic proteins inducing specific differentiation pathways. Moreover, hMSCs obtained from osteoporotic patients can restore their osteogenic activity following human BMP-2 gene transduction, an important finding in the future planning of gene therapy treatment for osteoporosis.

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III–V//Si multijunction solar cells offer a pathway to increase the power conversion efficiency beyond the fundamental Auger limit of silicon single‐junctions. In this work, we demonstrate how the efficiency of a two‐terminal wafer‐bonded III–V//Si triple‐junction solar cell is increased from 34.1 % to 35.9 % under an AM1.5g spectrum, by optimising the III–V top structure. This is the highest reported efficiency to date for silicon‐based multijunction solar cell technologies. This improvement was accomplished by two main factors. First, the integration of a GaInAsP absorber in the middle cell increased the open‐circuit voltage by 51 mV. Second, a better current matching of all subcells enhanced the short‐circuit current by 0.7 mA/cm2. Two different growth directions, upright and inverted, were investigated. The highest cell efficiency of 35.9 % (Voc = 3.248 V, jsc = 13.1 mA/cm2, FF = 84.3 %) was achieved with an upright grown structure. Processing of upright structures requires additional bonding steps, which results in a reduced homogeneity of cell performance across the wafer. A detailed comparison with the currently best triple‐junction solar cell reveals future improvement opportunities and limits, considering voltage and current, respectively.

Tunnel oxide passivating contacts (TOPCon) consisting of an ultrathin tunnel oxide capped by a doped Si film exhibit excellent passivation and contact properties. The application of these contacts has so far resulted in efficiencies of up to 25.7% realized with an n-type Si solar cell featuring a front-side boron-doped p + emitter and n-TOPCon as full-area rear electron contact. In this work, we study the same cell structure on p-type Si. In this case, the p + diffusion on the front acts as a front surface field (FSF) and the n-TOPCon layer as a full-area rear emitter. One benefit of this rear-junction cell design is that the whole base contributes to the hole transport towards the local contacts on the front, which means that the lateral current transport within the FSF is less important than in the case of the front emitter of the n-type cell. To study this, we addressed the influence of the FSF lateral conductivity on the performance of these rear-junction cells theoretically (based on a simulation study) as well as experimentally (with fabricated cells).Efficiencies up to 24.3% (independently confirmed) have been achieved with this structure applying a FSF and up to 23.9% without the full-area FSF. As such, these results demonstrate a high device performance for these TOPCon rear emitter cells even without a lateral conductivity in the FSF. This bears the potential to simplify the process chain quite substantially as no full-area boron diffusion is required.

Multijunction (MJ) solar cells achieve very high efficiencies by effectively utilizing the entire solar spectrum. Previously, we constructed a III‐V//Si MJ solar cell using the smart stack technology, a unique mechanical stacking technology with Pd nanoparticle array. In this study, we fabricated an InGaP/AlGaAs//Si three‐junction solar cell with an efficiency of 30.8% under AM 1.5G solar spectrum illumination. This efficiency is considerably higher than our previous result (25.1%). The superior performance was achieved by optimizing the structure of the upper GaAs‐based cell and employing a tunnel oxide passivated contact Si cell. Furthermore, we examined the low solar concentration performance of the device and obtained a maximum efficiency of 32.6% at 5.5 suns. This performance is sufficient for realistic low concentration photovoltaic applications (below 10 suns). In addition, we characterize the reliability of the InGaP/AlGaAs//Si three‐junction solar cell with a damp heat test (85 °C and 85% humidity for 1000 h). It was confirmed that our solar cells have high long‐term stability under severe conditions. The results demonstrate the potential of GaAs//Si MJ solar cells as next‐generation photovoltaic cells and the effectiveness of smart stack technology in fabricating multijunction cells.

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