ABSTRACT
Organic/inorganic hybrid solar cells are gaining attraction as the alternative technology demanding the supplement of clean, sustainable, and stable energy in recent years. In general, the hybrid solar cells consist of both organic and inorganic materials that create the p–n junction for separating the photogenerated carriers as the core constitute. Arrangement of poly(3,4-ethylenedioxythiophene), poly(styrenesulfonate) (PEDOT:PSS) polymer, and n-type crystalline silicon (Si) was proposed as the preference in hybrid structures considering the superiorities in fabrication aspect, reliability, and sound efficiency. As the main active component in p–n junction, however, a pristine PEDOT:PSS layer exhibits low electrical conductivity, with a value in the range of 0.2–10 S cm−1, which particularly causes the poor device performance in photovoltaic applications. Moreover, the adhesion capability of untreated PEDOT:PSS solutions to deposit on hydrophobic substrates generally yields the nonuniform contact. In this regard, several approaches enhancing the electrical and adhesion capability of pristine PEDOT:PSS are still in progress, and the chemical treatment is highly demanded, which allows the low cost and the large-area production based on the solution-processing capability. For example, it has been found that the electrical conductivity of treated PEDOT:PSS layer was remarkably improved up to 938 S cm−1 by employing a facile method through the incorporation of ethylene glycol as the cosolvents. Direct mixing of 7 wt% EG in precursors results in the optimum conductivity up to 103 orders of magnitude for the reduction in the sheet resistance. The transmittance of deposited PEDOT:PSS films achieves more than 90% for the improvement of corresponding transparency in the visible-frequency region. It is also found that the superior enhancement of conductivity can be attributed to doping mechanism, conformational changes of PEDOT segment, alteration of PEDOT:PSS arrangement, and the removal of excess insulating PSS chains from the PEDOT:PSS film. Based on the treatment of PEDOT:PSS film as a p-type component in hybrid solar cells, the explicit efficiency improvement of photovoltaic cells achieving >14% can be realized by the well management of electrical and optical properties of PEDOT:PSS layer.
