• Energy Research

We combine inkjet printed silver grids and reverse nanoimprinting transfer to demonstrate front electrode structures embedded within the substrate for indium tin oxide (ITO) replacement in organic solar cells. The smooth interface between Ag grid and transparent semiconductor polymer PEDOT:PSS improves the topology of the successive layers. In turn, this results in overall good photovoltaic performance including high fill factor and no shunting. By modelling the shadowing and resistive losses as a function of the separation between grid lines, the optimal grid structure is identified, which we then confirm experimentally. Inkjet printed ITO-free solar cells showed slightly higher performance than the ITO based reference. This work was financially supported by the Spanish Ministerio de Economía y Competitividad through projects MAT2009-10642, MAT2012-37776 and Cetemmsa Technological Centre (Project no. CSIC-20091449). I.B.C wishes to thank the Universitat Autònoma de Barcelona (UAB) for the support given through the Chemistry Ph.D. programme. Peer Reviewed

By combining X-ray absorption fine structure and X-ray diffraction measurements with density functional and molecular dynamics simulations, we study the structure of a set of AgxBi1−xS2 nanoparticles, a materials system of considerable current interest for photovoltaics. An apparent contradiction between the evidence provided by X-ray absorption and diffraction measurements is solved by means of the simulations. We find that disorder in the cation sublattice induces strong local distortions, leading to the appearance of short Ag–S bonds, the overall lattice symmetry remaining close to hexagonal.

We investigate the employment of carefully selected solvent additives in the processing of a commercial perovskite precursor ink and analyze their impact on the performance of organometal trihalide perovskite (CH3NH3PbI3−xClx) photovoltaic devices. We provide evidence that the use of benzaldehyde can be used as an effective method to preserve the stoichiometry of the perovskite precursors in solution. Benzaldehyde based additive engineering shows to improve perovskite solid state film morphology and device performance of CH3NH3PbI3−xClx based solar cells.

Perovskite photovoltaics (PVs) have attracted attention because of their excellent power conversion efficiency (PCE). Critical issues related to large‐area PV performance, reliability, and lifetime need to be addressed. Here, it is shown that doped metal oxides can provide ideal electron selectivity, improved reliability, and stability for perovskite PVs. This study reports p‐i‐n perovskite PVs with device areas ranging from 0.09 cm2 to 0.5 cm2 incorporating a thick aluminum‐doped zinc oxide (AZO) electron selective contact with hysteresis‐free PCE of over 13% and high fill factor values in the range of 80%. AZO provides suitable energy levels for carrier selectivity, neutralizes the presence of pinholes, and provides intimate interfaces. Devices using AZO exhibit an average PCE increase of over 20% compared with the devices without AZO and maintain the high PCE for the larger area devices reported. Furthermore, the device stability of p‐i‐n perovskite solar cells under the ISOS‐D‐1 is enhanced when AZO is used, and maintains 100% of the initial PCE for over 1000 h of exposure when AZO/Au is used as the top electrode. The results indicate the importance of doped metal oxides as carrier selective contacts to achieve reliable and high‐performance long‐lived large‐area perovskite solar cells.

A detailed investigation of the functionality of inverted organic photovoltaics (OPVs) using bare Ag contacts as top electrode is presented. The inverted OPVs without hole transporting layer (HTL) exhibit a significant gain in hole carrier selectivity and power conversion efficiency (PCE) after exposure in ambient conditions. Inverted OPVs comprised of ITO/ZnO/poly(3-hexylthiophene-2,5-diyl):phenyl-C61-butyric acid methyl ester (P3HT:PCBM)/Ag demonstrate over 3.5% power conversion efficiency only if the devices are exposed in air for over 4 days. As concluded through a series of measurements, the oxygen presence is essential to obtain fully operational solar cell devices without HTL. Moreover, accelerated stability tests under damp heat conditions (RH=85% and T=65oC) performed to non-encapsulated OPVs demonstrate that HTL-free inverted OPVs exhibit comparable stability to the reference inverted OPVs. Importantly, it is shown that bare Ag top electrodes can be efficiently used in inverted OPVs using various high performance polymer:fullerene bulk heterojunction material systems demonstrating 6.5% power conversion efficiencies.

AbstractThe application of conjugated materials in organic photovoltaics (OPVs) is usually demonstrated in lab‐scale spin‐coated devices that are processed under controlled inert conditions. Although this is a necessary step to prove high efficiency, testing of promising materials in air should be done in the early stages of research to validate their real potential for low‐cost, solution‐processed, and large‐scale OPVs. Also relevant for approaching commercialization needs is the use of printing techniques that are compatible with upscaling. Here, solution processing of organic solar cells based on three new poly(2,7‐carbazole) derivatives is efficiently transferred, without significant losses, to air conditions and to several deposition methods using a simple device architecture. High efficiencies in the range between 5.0 % and 6.3 % are obtained in (rigid) spin‐coated, doctor‐bladed, and (flexible) slot‐die‐coated devices, which surpass the reference devices based on poly[N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] (PCDTBT). In contrast, inkjet printing does not provide reliable results with the presented polymers, which is attributed to their high molecular weight. When the device area in the best‐performing system is increased from 9 mm2 to 0.7 cm2, the efficiency drops from 6.2 % to 5.0 %. Photocurrent mapping reveals inhomogeneous current generation derived from changes in the thickness of the active layer.