Polymer solar cells (PSCs) have been extensively studied because of their potential in satisfying the growing consumption of sustainable energy by mankind [
1,
2]. Considerable effort has been devoted to the commercialization of PSCs [
3]. The power conversion efficiency (PCE) of PSCs has improved rapidly over the past several years with the development of new donors [
4,
5] and acceptors [
6], applications of new device structures [
7], and interface engineering [
8–
11]. Moreover, the highest PCE of single-junction PSCs has exceeded 12% [
12]. The indium tin oxide (ITO) electrode is the most widely used electrode in PSCs because of its high conductivity, excellent transparency, and compatibility with organic semiconducting materials, but its high cost and poor flexibility limits further application [
13]. For satisfying the demand for high conductivity and transparency, low cost, flexibility, and portability, various new electrodes, such as conductive oxides [
14], conducting polymers [
15], carbon nanotube films [
16], graphene films [
17], metal nanostructures, and nanowire networks [
18,
19], have been studied.