POLYMORPHOUS/CRYSTALLINE SINGLE HETEROJUNCTION AND DOUBLE HETEROJUNCTION SOLAR CELLS OPTIMISATION ON P TYPE MONOCRYSTALLINE SILICON

摘要

An alternative way to conventional solar cell process is to develop a low temperature route using hydrogenated amorphous silicon (a-Si:H) thin film deposited by PECVD on bulk crystalline silicon. The French national project "PHARE" aims to improve polymorphous/crystalline (a-Si:H/ptn-Si:H/c-Si/a-Si:H) heterojunctions on p-type crystalline silicon (c-Si) to achieve large area solar cells for industrial application. We present the continuous improvements of the project. Low Temperature Screen-Printed pastes (LT-SP) are one of the key issues. Indeed, resistivity has to be improved and one of the options is to use a high level of silver in the paste. First textured single heterojunction cells are presented with reproducible and good I(V) characteristics. The analysis of the pm-Si:H/c-Si interface quality on textured substrates demonstrates that the wafer cleaning after KOH texturation is a crucial issue. First results on double heterojunction solar cells with aluminum on the back surface are presented. We show that an intrinsic amorphous thin layer on the back is not an interesting option. The internal quantum efficiency and reflectivity with and without the intrinsic layer are presented and confirm the I(V) analysis. Up to now, solar cells of 25 cm~2 area using CZ (Si) substrate, with textured cells and single heterojunction achieved efficiency of 16.2 % and V_(oc) = 641 mV and a maximum fill factor of 74 % with LT-SP from Dupont MCM. Double heterojunction solar cells achieved up to 650 mV and maximum efficiency of 16.8 % on polished wafers.