Carbon nanotube networks as efficient transparent electrode for polymer/silicon hybrid solar cells

Polymer/Si hybrid solar cells have attracted much research interest in virtue of their simple device structure and combination of flexibility and stability. Metal grid by thermal evaporation is usually used as the top electrode, which gives rise to a tradeoff between the efficient coverage and the decreased light absorption, in addition to the costly metal deposition in high vacuum. Carbon nanotube (CNT) networks possess both good conductivity and high light transmittance, thus is a promising candidate for the top electrode. Although it is significant to prepare and apply large-area and high-quality CNT films with high transparency and low sheet resistances into kinds of solar cells, CNTs have not been studied as transparent electrodes in polymer/Si hybrid solar cells to the best of our knowledge. In this work, large-area and continuous CNT networks with 86% transmittance at 550 nm are synthesized and used as transparent window electrodes in the hybrid heterojunction solar cells composed of a conjugate polymer poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) and micro-textured n-type crystalline silicon wafers. Directly laminating the pristine CNT film onto the PEDOT:PSS/Si surface can lead to a power conversion efficiency (PCE) of 3.9%. After purification of CNT networks, the performance is improved up to 7.0%, due to the efficient carrier transportation and light harvesting of CNT electrodes. The results indicate that the flexible and transparent CNT networks have great potential for realizing metal grid-free hybrid polymer/Si solar cells.