Hole diffusion length and temperature dependence of photovoltages for n-Si electrodes modified with LB layers of ultrafine platinum particles

The mechanism of generation of high open-circuit photovoltages ( V oc s) of 0.62–0.63 V for n-Si (~ 1 Ω cm) electrodes modified with colloidal Pt particles (4 nm in diameter) is investigated by measurements of minority-carrier (hole) diffusion length ( L p ) and temperature dependence of V oc . Langmuir-Blodgett (LB) layers of colloidal Pt particles are used to control the Pt density on n-Si. The L p value is determined to be 200 μm, irrespective of whether n-Si is modified with Pt or not. The temperature dependences of V oc s at 203–298 K have been explained well by our previously proposed model. It is shown that heat treatments of the Pt-modified n-Si electrodes increase the area and the width of the direct Pt-Si contacts and thus decrease V oc , but minority-carrier controlled (ideal) solar cells are obtained if the electrodes are prepared under appropriate conditions.