Organic solar cells have unique properties that make them very attractive as a renewable energy source. Of particular interest are semi-transparent cells, which have the potential to be integrated into building façades yet not completely block light. However, making organic cells transparent limits the metal electrode thickness to a few nanometres, drastically reducing its reflectivity and the device photon-harvesting capacity. Here, we propose and implement an ad hoc path for light-harvesting recovery to bring the photon-to-charge conversion up to almost 80% that of its opaque counterpart. We report semi-transparent PTB7:PC 71 BM cells that exhibit 30% visible light transmission and 5.6% power conversion efficiency. Non-periodic photonic crystals are used to trap near-infrared and near-ultraviolet photons. By modifying the layer structure it is possible to tune the device colour without significantly altering cell performance.

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UPCommonsPortal del coneixement obert de la UPC http://upcommons.upc.edu/e-prints Abstract: We studied the performance over time of opaque and semi-transparent PTB7:PC71BM bulk hetero-junction solar cells. For unsealed inverted configuration cells we observe that when the isolation from the environment is improved, the degradation observed is dominated by one single exponential decay. We demonstrate that a dielectric multilayer stack of approximately 550 nm provides an isolation that increases the lifetime of the cell close to ten times. In that event the fill factor appears to be the PV parameter dominating cell degradation resulting from a decrease in the shunt resistance. An Impedance analysis we performed indicates that a Warburg element, attributed to the presence of slowly moving charges such as heavy ions, must be included in thedescription of the experimental data. The contribution from such element increases as the cell degrades in good agreement with a degradation dominated by the corrosive effects from external agents reaching the active layer of the device. We have revised our manuscript according to the comments and suggestions from both reviewers. Enclosed with the manuscript we provide a detailed response to the reviewers points. Essentially, we do not have any strong disagreement with the reviewers remarks and we used their comments and suggestions to improve the manuscript. In response to the request of an ISOS-L-1 test made by reviewer#3, we provide a supplementary data file which is cited in the revised main text. With the submission we provide a detailed response to the reviewers points and an indication of the changes introduced. Additionally, we provide a copy of the text where all changes introduced are in blue.We would like to use this opportunity to thank you again for all the time and consideration dedicated to our manuscript. In the first paragraph in page 6 of the revised manuscript the following sentenceis included: For V< 0,6 V the Warburg feature is not observed and therefore R w is set to 0. The second paragraph in page 6 has been rewritten as follows: Nyquist plots at four different voltages are shown in figures 6 as examples of impedance measurements for three different times. We observe a good agreement between the experimental data and the theoretical fit. The main feature in the complex plane is a typical depressed semicircle in the medium-high frequency range, a standard behaviour in organic solar cells associated to carrier recombination. The semicircle diameter increases with time, which implies an increase of the parallel resistance R P . This leads to a corresponding rise of the recombination time and therefore to an enhancement of the carrier density. Besides, the semicircle depression is more pronounced with time, leading to a decrease of CPE P parameter, and thus moving away from the ideal capacitor behaviour. At low frequencies, for V = 0.6 and 0.8 V, one may observe a tail associated to a Warburg behaviour that is more pronounced as time evolves. This results in an ...

We report a photovoltaics-electrochemical (PV-EC) assembly based on a compact and easily processable triple homo-junction polymer cell with high fill factor (76%), optimized conversion efficiencies up to 8.7 % and enough potential for the energetically demanding water splitting reaction (Voc = 2.1 V). A platinum-free cathode made of abundant materials is coupled to a ruthenium oxide on glassy carbon anode (GC-RuO 2 ) to perform the reaction at optimum potential (ΔE = 1.70-1.78 V, overpotential = 470-550 mV). The GC-RuO 2 anode contains a single monolayer of catalyst corresponding to a superficial concentration (Γ) of 0.15 nmol cm -2 and is highly active at pH 7. The PV-EC cell achieves solar to hydrogen conversion efficiencies (STH) ranging from 5.6 to 6.0 %. As a result of the solar cell's high fill factor, the optimal photovoltaic response is found at 1.70 V, the minimum potential at which the electrodes used perform the water splitting reaction. This allows generating hydrogen at efficiencies that would be very similar (96%) to those obtained as if the system were to be operating at 1.23 V, the thermodynamic potential threshold for the water splitting reaction.

An optically enhanced architecture can be used to fabricate high‐performance polymer solar cells. The basic optical parameters that control light propagation in a layered device are such that an optimal light harvesting is achieved. The general character of such optically enhanced architecture is demonstrated by applying it to two different kinds of low bandgap polymers.