A back contact photovoltaic cell comprising - a semi-conductor body having a first and second surface opposite to each other; - a first and second two-dimensional array of contact points (12, 14) on the first surface, each coupled to a respective one of base and emitter areas in or on the semi-conductor body; - electrically separate first and second conductor structures, both on the first surface, coupled to contact points (12, 14) of the first and second two-dimensional array respectively; - the first conductor structure comprising sets of first conductor line branches, the first conductor line branches of each set branching out into a tree structure from a respective one of the contact points of the first two-dimensional array, with branch conductor lines in at least three successive different directions at less than a hundred and eighty degrees to each other, the tree structure having increasing numbers of branch conductor lines with increasing distance from the respective one of the contact points; - the second conductor structure comprising second conductor line branches in at least three different directions in areas between respective pairs of adjacent ones of the first conductor line branches, the first conductor line branches of different ones of the respective pairs being non parallel to the first conductor line branches of other ones of the respective pairs, each second conductor line branch coupled at least to a respective one of the contact points of the second two-dimensional array, wherein the second conductor line branches extend to areas between each pair of adjacent branches in the tree structure. - a semi-conductor body having a first and second surface opposite to each other; - a first and second two-dimensional array of contact points (12, 14) on the first surface, each coupled to a respective one of base and emitter areas in or on the semi-conductor body; - electrically separate first and second conductor structures, both on the first surface, coupled to contact points (12, 14) of the first and second two-dimensional array respectively; - the first conductor structure comprising sets of first conductor line branches, the first conductor line branches of each set branching out into a tree structure from a respective one of the contact points of the first two-dimensional array, with branch conductor lines in at least three successive different directions at less than a hundred and eighty degrees to each other, the tree structure having increasing numbers of branch conductor lines with increasing distance from the respective one of the contact points; - the second conductor structure comprising second conductor line branches in at least three different directions in areas between respective pairs of adjacent ones of the first conductor line branches, the first conductor line branches of different ones of the respective pairs being non parallel to the first conductor line branches of other ones of the respective pairs, each second conductor line branch coupled at least to a respective one of the contact points of the second two-dimensional array, wherein the second conductor line branches extend to areas between each pair of adjacent branches in the tree structure.