Events

Understanding the role of hole-transport materials on the performance of perovskite solar cells*

September 24, 2015 at 2 pm/35-520

Becky Belisle
Stanford University

Since the recent emergence of perovskite solar cells and their demonstration as highly promising photovoltaics, much work has been done to tune and improve the device-architecture in the hopes of achieving even higher power conversion efficiencies. One main effort in changing the architecture of these PIN-type solar cells has been to replace the p-type selective contact, most commonly the organic hole-transport material (HTM) Spiro-OMeTAD, with an alternative material. Though there are several desirable reasons to replace Spiro-OMeTAD, the high manufacturing cost and poor device stability being chief among them, one that is often touted is the potential to achieve a higher Voc by switching to a higher ionization potential HTM. In this study we investigate this last point, probing more deeply the effects of varying the doping and ionization potential of the HTM on performance metrics including Voc. We study this change through a combination of experimental and modeling techniques. We first fabricated a series of TiO2/CH3NH3PbI3/HTM devices made with varying HTMs (Spiro-OMeTAD and α-NPD of varying doping concentrations) to empirically test the effect of changing HTM. We then used a drift-diffusion modeling package, SCAPS, to develop a device model that fits the observed trends and provides a greater understanding of the role of a HTM on the photovoltaic performance of these devices. Notably, we find that a perovskite device dominated by recombination at an electron trap best describes our observed trends, and a principal role of the HTM is controlling the population of these traps. Understanding this behavior allows us to develop designs rules for HTMs that minimize recombination, and therefore maximize the Voc. Overall this work lends useful insights into HTM optimization for devices made with CH3NH3PbI3, and looking forward can help us rationally design good architectures for alternative perovskites of varying band gaps.

Becky Belisle is a graduate student in the McGehee Group in the Department of Materials Science & Engineering at Stanford University, CA.

*This talk is part of the Perovskites Seminar Series organized by Sam Stranks and sponsored by the Center for Excitonics. For more info contact Sam: stranks@mit.edu