How contact layers control shunting losses from pinholes in thin-film solar cells

Journal article

An absorber layer that does not fully cover the substrate is a common issue for thin-film solar cells such as perovskites. However, models that describe the impact of pinholes on solar cell performance are scarce. Here, we demonstrate that certain combinations of contact layers suppress the negative impact of pinholes better than others. The absence of the absorber at a pinhole gives way to a direct electrical contact between the two semiconducting electron and hole transport layers. The key to understand how pinholes impact the solar cell performance is the resulting nonlinear diodelike behavior of the current across the interface between these two layers (commonly referred to as a shunt current). Based on experimentally obtained data that mimic the current–voltage characteristics across these interfaces, we develop a simple model to predict pinhole-induced solar cell performance deterioration. We investigate typical contact layer combinations such as TiO2/spiro-OMeTAD, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)/phenyl-C61-butyric acid methyl ester, and TiO2/poly(3-hexylthiophene). Our results directly apply to perovskite and other emerging inorganic thin-film solar cells, and the methodology is transferable to CIGS and CdTe. We find substantial differences between five commonly applied contact layer combinations and conclude that it is not sufficient to optimize the contact layers of any real-world thin-film solar cell only with regard to the applied absorber. Instead, in the context of laboratory and industrial fabrication, the tolerance against pinholes (i.e., the mitigation of shunt losses via existing pinholes) needs to be considered as an additional, important objective.

Authors: Kaienburg, P; Hartnage, P; Pieters, BE; Yu, J; Grabowski, D

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Chemical Society
• Journal: Journal of Physical Chemistry C
• Volume: 122
• Issue: 48
• Pages: 27263-27272
• Publication date: 2018-11-09
• Acceptance date: 2018-11-06
• DOI: 10.1021/acs.jpcc.8b09400
• EISSN: 1932-7455
• ISSN: 1932-7447
• Language: English
• Keywords: FFR