Transparent photovoltaics are garnering significant interest for power generation in applications in building integrated photovoltaics (BIPV), including solar windows and other shading elements. Metal halide perovskites have emerged as one of the most lucrative material classes for such device architectures due to their exceptional optoelectronic properties, compositional versatility enabling a wide range of transparency levels, and low power to weight ratio.[1] Traditionally, research has primarily focused on semi-transparent (ST) solar cell architectures, where transparency is managed by either adjusting the perovskite layer thickness or by increasing the bandgap, yet their coloured appearance as well as efficiency and stability limitations hinder their practical applicability. Here, we focus on an alternative approach to realize both efficient and colour-neutral, transparent perovskite solar cells (PSC) by utilising a fully opaque device which is partially covering the surface, i.e. semi-opaque (SO). This approach is especially appealing since under ideal conditions the generated power by a SO cell is linearly proportional to the aerial coverage, and therefore the efficiency limits are derived from the fully opaque device performance.

We begin by conducting a computational comparative analysis between ST-PSC and SO-PSC configurations based on their predicted performance by means of the trade-off between power conversion efficiency (PCE) and average visual transmittance (AVT), as well as their aesthetic appearance through the CIE colour coordinates and colour rendering index (CRI).[2] Our results show that based on practical literature limits, SO devices are predicted to yield superior performance compared to ST-PSCs at transparencies below ~60% AVT.

One of the biggest challenges to realize efficient SO-PSCs is the fabrication of multi-layered patterned perovskite architectures within the best performing device configurations. This key hurdle stems mostly from the sensitivity of organo-metallic perovskites to conventional lithographic processes.[3] Motivated by this gap, we developed a scalable patterning method that allows a controlled self-assembly of the perovskite solution via a simple stamping step. Through micro-contact printing of the substrate with a hydrophobic template comprising octadecylphosphonic acid molecules, the perovskite solution is constrained to crystallize only in the desired regions, thus allowing for a quick fabrication of patterned films without requiring any post deposition processing.[4]

Utilising this approach, SO-PSCs were fabricated with varying levels of transparency between 20-50%. Our preliminary results demonstrate minimal loss per active area relative to fully opaque devices, indicating the potential of this patterning approach. Moreover, we show that by applying an antireflective coating on both sides, the overall transparency is significantly improved through both reduced reflection from the front side and increased light outcoupling from the back side. Compared to literature benchmarks, these devices are well on-par with the best performing ST and SO devices reported to date, while exhibiting the highest efficiency for color-neutral PSC over a wide transparency range.