Energy-Harvesting Asymmetry in Semitransparent Polymer Solar-Cells Based on a Laminated Transparent Electrode

Abstract

Semitransparent polymer solar cells (ST-PSCs) with laminated transparent electrodes are promising candidates for building-integrated photovoltaics. However, the optical mechanisms governing their bidirectional performance remain underexplored. We systematically investigated the photovoltaic response of a vacuum-free laminated transparent electrode (LTE) comprising PEDOT:PSS/silver nanowire (AgNW) integrated with a PTB7:PC71BM photoactive layer (PAL) under top-side and bottom-side illumination. External quantum efficiency (EQE) measurements combined with transfer-matrix (TMM) optical simulations were used to deconvolute the optical and electrical contributions to the observed performance asymmetry. A 20.5% photocurrent reduction was measured upon top-side illumination (9.24 mA cm−2) compared with bottom-side (11.63 mA cm−2), which optical simulations attributed to wavelength-dependent parasitic absorption in the PEDOT:PSS/AgNW thin layer (300–450 nm) and to interfacial exciton quenching combined with the LTE’s direct proximity to the PAL. The open-circuit voltage remained nearly invariant across both illumination directions, demonstrating that the vacuum-free lamination process preserved the electronic integrity of the active layer. The device achieved 3.79% power conversion efficiency with 36.9% average visible transmittance. The introduction of a diffuse scattering paper layer at the rear recovered 10.1% of the lost photocurrent through photon recycling, thereby increasing the short-circuit current density to 12.80 mA cm−2 and efficiency to 4.45%. These findings establish the dominant optical loss mechanisms in laminated transparent electrodes and demonstrate a scalable light-management strategy for enhancing the semitransparent photovoltaic performance.