The emerging dye-sensitized solar cells, perovskite solar cells, and organic solar cells have been regarded as promising photovoltaic technologies. The device structures and components of these solar cells are imperative to the device’s efficiency and stability. Polymers can be used to adjust the device components and structures of these solar cells purposefully, due to their diversified properties. In dye-sensitized solar cells, polymers can be used as flexible substrates, pore- and film-forming agents of photoanode films, platinum-free counter electrodes, and the frameworks of quasi-solid-state electrolytes. In perovskite solar cells, polymers can be used as the additives to adjust the nucleation and crystallization processes in perovskite films. The polymers can also be used as hole transfer materials, electron transfer materials, and interface layer to enhance the carrier separation efficiency and reduce the recombination. In organic solar cells, polymers are often used as donor layers, buffer layers, and other polymer-based micro/nanostructures in binary or ternary devices to influence device performances. The current achievements about the applications of polymers in solar cells are reviewed and analyzed. In addition, the benefits of polymers for solar cells, the challenges for practical application, and possible solutions are also assessed.

A two-step cyclic voltammetry (CV) approach is employed in a quick and controllable electropolymerization of polyaniline (PANI) nanofibers with a short-branched structure onto fluorinated tin oxide (FTO) glass substrates as counter electrodes (CEs) for Pt-free dye-sensitized solar cells (DSSCs). In the two-step CV method, a small quantity of PANI as a function of the crystal nucleus in the crystal growth, is pre-electropolymerized under a suitably high potential for one cycle at the first-step, then subjected to the second-step for PANI electropolymerization at a low potential for a small number of scans. The well-controlled PANI nanofibers with high performance can be electropolymerized quickly using the two-step mode. The extensive CVs demonstrate the two-step PANI CE has superior electrocatalytic activity for the I₃ ⁻ reduction. Moreover, electrochemical impedance spectroscopy shows that the two-step PANI CE has a lower series resistance and charge-transfer resistance than the PANI CE prepared by conventional one-step CV electropolymerization. Therefore, the DSSC assembled with the two-step PANI CE exhibits an enhanced photovoltaic conversion efficiency of 6.21% (compared to 5.01% for the DSSC with the one-step PANI CE), up to ∼97% of the level of the DSSC using Pt CE. As the result, the two-step CV electropolymerized PANI CE can be considered as a promising alternative CE for Pt-free DSSCs.

The electrospun TiO ₂ nanofibers can provide direct pathways for the rapid collection and transmission of photogenerated electrons. These can also be conducive to the absorption and utilization of sunlight.