Solar cell manufacturers have been increasing sheet resistance to improve current and voltage by increasing blue response and decreasing recombination.
Narrower finger lines that are spaced closer together are required for the front grid design to account for the higher sheet resistance and allow minimal shading of the light absorbing region.
In addition, the cross sectional area of the conductive traces must transport current with low line resistance, so increased height is required. The relation of height versus width is defined as aspect ratio.