Spatial Distribution of Solar Cell Parameters in Multigrain Halide-Perovskite Films: A Device Model Perspective

Abstract

The polycrystalline nature of perovskite thin films suggests that the nonradiative recombination losses may be grain size dependent. We use measured grain size distributions of methylammonium lead triiodide layers to describe the macroscopic solar cell as composed of multiple single grain size cells operating in parallel. Using a model, we show that the grain size distribution results in spatial dispersion of the local open-circuit voltage (0.9–1.15 V), fill factor (50–82%), and power conversion efficiency (7.5–19%). When the device is held at open-circuit voltage, there is significant current exchange between large and small grains. Smaller grains are a “parasitic shunt” for the larger grains.

Understanding the Impacts of Grain Size Variation, Distribution, and Recombination Losses in Halide Perovskites: A Generalized Semi‐Analytical Model from Thin‐Film to Photovoltaics

“…[71] However, this exchange evolved through contacts, not among grains. [52] Depending on the nature of interfaces between contacts and grains or between adjacent grains, one may find a different result than what is presented here. So, this is where engineering grains come into play.…”

“…Recently, there has been a lot of excellent works describing the relation of recombination losses to FF (sheet and shunt resistance). [49][50][51][52] However, the approach is still empirical, so this correlation might be different from sample to sample or may not be unique to a certain composition. The generalized model in Equation ( 9) can be expanded if the relation of J sc and FF to the recombination at grain boundary is well understood.…”

“…[ 50,51 ] It is also predicted that the local open‐circuit voltage, fill‐factor, and power‐conversion efficiency of halide perovskite PVs is strongly affected by spatial dispersion of grain sizes. [ 44,52 ] This result is really encouraging because most defect mitigation works in halide perovskite (both experimental and simulation) include only partially the effect of grain size, distribution, and recombination velocity at all interfaces. [ 16,40,53–55 ] Nevertheless, this has improved our understanding of to what extent the record cell efficiency can be increased even further.…”

Perovskite ionics – elucidating degradation mechanisms in perovskite solar cells via device modelling and iodine chemistry

“…Specifically, this was achieved by choosing the BLs' energy levels to perfectly align with the respective energy levels of the active perovskite layer. We implemented only radiative processes for recombination, and the SRH-type recombination 48,49 is not included. This allows us to show that the electrochemical reactions introduce SRH-type recombination.…”

Towards low-temperature processing of efficient γ-CsPbI3 perovskite solar cells

“…This indicates that samples with too much Pb(OAc) 2 excess might exhibit higher recombination losses, resulting in a lower V OC and FF and, consequently, an overall inferior efficiency. 44,64,65 Optimization of hole transport layers for CsPbI 3 PSCs Considering that the choice of substrates may strongly impact on the perovskite lm formation, [66][67][68] we chose the X = 1.2 stoichiometry samples to investigate four different hole transport layers (HTLs): inorganic (NiO x ), polymer (PTAA), selfassemble monolayers (SAMs, MeO-2PACz, in the following termed 'MeO 2 '), and inorganic/SAMs hybrids (NiO x /MeO 2where the NiO x layer is rst deposited on ITO and then coated with a MeO 2 SAM). As is detailed in the Experimental section, these HTLs were spin-coated on pre-cleaned ITO substrates prior to the deposition of the perovskite layer.…”