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36th European Photovoltaic Solar Energy Conference and Exhibition; 214-218, We examine the impact of Sorbitol admixture on the hole conductive polymer PEDOT:PSS[poly(3,4ethylenedioxythiophene):poly(styrenesulfonate)] in combination with a variation of the annealing duration. As demonstrated in a previous publication, the admixture of Sorbitol to the PEDOT:PSS dispersion is improving the transparency of the organic layer and is also improving the surface passivation. On the other hand, the contact resistance on the silicon surface tends to increase by admixture of Sorbitol. In this study, we fabricate solar cells where the PEDOT:PSS layer is used as a hole-selective contact at the cell rear (so-called ‘BackPEDOT’ solar cells). The electron-selective front is conventionally processed by means of phosphorus diffusion. The passivation of the silicon surface with PEDOT:PSS:Sorbitol shows an improvement in the passivation quality and the solar cells show an increasing open-circuit voltage Voc by increasing the annealing duration from the previously routinely applied 10 min to 60 min. The short-circuit current density Jsc of the fabricated solar cells remains unchanged for all investigated annealing durations. Importantly, the series resistance Rs (and hence the contact resistance) of the fabricated BackPEDOT solar cells show a minimum for annealing durations between 45 and 90 min. As a consequence, increasing the annealing duration led to an increased maximum energy conversion efficiency of 20.6% at one sun.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 85-88, In this contribution, we first give a brief historical overview of the recent developments on polymer/silicon heterojunction cells. We then focus on our most recent results concerning: (i) the PEDOT:PSS/c-Si interface design, where the thickness of the native oxide in-between the c-Si surface and the polymer is shown to play a crucial role, (ii) a new type of heterojunction cell, where the hole-selective layer is PEDOT:PSS and the electronselective layer is well-passivating phosphorus-doped amorphous silicon (n-a-Si:H), (iii) the stability of the polymer/silicon cells in ambient environment. We demonstrate for the first time that the efficiencies of BackPEDOT cells are long-term stable if a metal foil is used as rear metallization scheme, as the metal foil does not transmit any humidity in contrast to evaporated metals. (iv) We present first results of our attempt to implement a PEDOT:PSS/c- Si junction into an industrial-type large-area (15.6×15.6 cm2) screen-printed c-Si solar cell and reach an efficiency of 19.5% in our first batch of cells.