TY - JOUR A1 - Albrecht, Steve A1 - Grootoonk, Bjorn A1 - Neubert, Sebastian A1 - Roland, Steffen A1 - Wordenweber, Jan A1 - Meier, Matthias A1 - Schlatmann, Rutger A1 - Gordijn, Aad A1 - Neher, Dieter T1 - Efficient hybrid inorganic/organic tandem solar cells with tailored recombination contacts JF - Solar energy materials & solar cells : an international journal devoted to photovoltaic, photothermal, and photochemical solar energy conversion N2 - In this work, the authors present a 7.5% efficient hybrid tandem solar cell with the bottom cell made of amorphous silicon and a Si-PCPDTBT:PC70BM bulk heterojunction top cell. Loss-free recombination contacts were realized by combing Al-doped ZnO with either the conducting polymer composite PEDOT:PSS or with a bilayer of ultrathin Al and MoO3. Optimization of these contacts results in tandem cells with high fill factors of 70% and an open circuit voltage close to the sum of those of the sub-cells. This is the best efficiency reported for this type of hybrid tandem cell so far. Optical and electrical device modeling suggests that the efficiency can be increased to similar to 12% on combining a donor polymer with suitable absorption onset with PCBM. We also describe proof-of-principle studies employing light trapping in hybrid tandem solar cells, suggesting that this device architecture has the potential to achieve efficiencies well above 12%. (C) 2014 Elsevier B.V. All rights reserved. KW - Hybrid solar cells KW - Tandem solar cells KW - Organic solar cells KW - Bulk heterojunction KW - Efficiency optimization Y1 - 2014 U6 - https://doi.org/10.1016/j.solmat.2014.04.020 SN - 0927-0248 SN - 1879-3398 VL - 127 SP - 157 EP - 162 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Albrecht, Steve A1 - Schaefer, Sebastian A1 - Lange, Ilja A1 - Yilmaz, Seyfullah A1 - Dumsch, Ines A1 - Allard, Sybille A1 - Scherf, Ullrich A1 - Hertwig, Andreas A1 - Neher, Dieter T1 - Light management in PCPDTBT:PC70BM solar cells: A comparison of standard and inverted device structures JF - Organic electronics : physics, materials and applications N2 - We compare standard and inverted bulk heterojunction solar cells composed of PCPDTBT:PC70BM blends. Inverted devices comprising 100 nm thick active layers exhibited short circuit currents of 15 mA/cm(2), 10% larger than in corresponding standard devices. Modeling of the optical field distribution in the different device stacks proved that this enhancement originates from an increased absorption of incident light in the active layer. Internal quantum efficiencies (IQEs) were obtained from the direct comparison of experimentally derived and modeled currents for different layer thicknesses, yielding IQEs of similar to 70% for a layer thickness of 100 nm. Simulations predict a significant increase of the light harvesting efficiency upon increasing the layer thickness to 270 nm. However, a continuous deterioration of the photovoltaic properties with layer thickness was measured for both device architectures, attributed to incomplete charge extraction. On the other hand, our optical modeling suggests that inverted devices based on PCPDTBT should be able to deliver high power conversion efficiencies (PCEs) of more than 7% provided that recombination losses can be reduced. KW - Organic solar cells KW - Inverted solar cells KW - PCPDTBT KW - Low band-gap KW - Optical modeling Y1 - 2012 U6 - https://doi.org/10.1016/j.orgel.2011.12.019 SN - 1566-1199 VL - 13 IS - 4 SP - 615 EP - 622 PB - Elsevier CY - Amsterdam ER -