High‑Efficiency, Low‑Cost Perovskite Solar Cells: Progress, Challenges, and Future Directions

Introduction

Today, about 85% of global energy consumption derives from fossil fuels, contributing to environmental degradation and health risks. Projections estimate that global energy demand will double by 2050 [1]. In response, renewable power—wind, hydro, and solar—has become an urgent priority. In 2014, renewable‑based generation capacity additions reached 128 GW, with wind at 37%, solar at ~33%, and hydro above 25% [Fig. 1a]. Solar energy’s low cost and environmental friendliness have spurred rapid advances in PV research.

a Global renewable‑based power capacity additions by type and share of total capacity additions [60]. b Rapid PCE evolution of perovskite solar cells from 2009 to 2016.

PV technologies are traditionally categorized into three generations: first‑gen wafer‑based (mono‑c‑Si, mc‑Si), second‑gen thin film (a‑Si, CdTe, CIGS, CuGaSe), and third‑gen multi‑junction, organic, dye‑sensitized, and quantum‑dot devices [2]. While silicon PV is mature, incremental efficiency gains are limited. III‑V cells achieve high efficiencies but at prohibitive cost [7–9]. Quantum‑dot cells promise low cost and high performance, yet many rely on toxic heavy metals [10–12]. Halide perovskites have emerged as a transformative, low‑cost material, with efficiencies rising from 3.8% in 2009 to 22.1% in 2016 [13–16]. Nonetheless, long‑term stability remains a barrier to commercialization.

This review outlines PSC history, recent efficiency breakthroughs, stability challenges, and interface‑engineering strategies.

Principle and History of Perovskite SCs

PSCs combine the low‑cost, high‑efficiency advantages of dye‑sensitized solar cells (DSSCs) with halide perovskite absorbers. The field was sparked by O’Regan and Grätzel’s 1991 DSSC breakthrough (~7% efficiency) [17], inspiring the first perovskite‑based DSSCs in 2009 [13]. Early devices, however, suffered from low efficiency and poor stability due to liquid‑electrolyte hole transport layers (HTLs).

a Crystal structure of a perovskite [22]. b General PSC device schematic [23]. c SEM of meso‑superstructured PSC (scale 500 nm) [22]. d SEM of planar PSC with HTL/ETL [22].

In 2012, Kim, Grätzel, and Park pioneered solid‑state meso‑superstructured PSCs using Spiro‑MeOTAD and mp‑TiO₂ as HTM and ETM, achieving 9.7% efficiency [14]. Subsequent advances raised single‑junction PSC efficiencies to 22.1% in 2016, approaching the 31.4% theoretical limit for CH₃NH₃PbI₃₋ₓClₓ [19].

PSC architecture typically includes an ITO/FTO substrate, perovskite active layer, HTL, ETL, and electrodes. Two dominant architectures are meso‑superstructured (MPSCs) and planar (PPSCs) [24, 25]. The operating principle involves light absorption in the perovskite, generation of electron–hole pairs, charge extraction by ETM/HTM, and collection at electrodes.

High‑Efficiency Perovskite Solar Cells

Intramolecular Exchange

In June 2015, Yang et al. introduced a direct intramolecular exchange method to grow high‑quality FAPbI₃ films, achieving 20.1% PCE under AM 1.5 G illumination [26]. The process replaces DMSO molecules intercalated in PbI₂ with formamidinium iodide, yielding (111)‑oriented, large‑grain, defect‑free perovskite layers.

a Schematic of FAPbI₃ crystallization via intramolecular exchange. b Efficiency histogram of 66 FAPbI₃ cells fabricated by IEP vs. conventional process [26].

Cesium‑Containing Triple‑Cation Perovskite Solar Cells

Saliba et al. demonstrated that incorporating cesium into triple‑cation perovskite compositions (Csₓ(MA₀.₁₇FA₀.₈₃)₁₀₀₋ₓPb(I₀.₈₃Br₀.₁₇)₃) yields >21% PCE, enhanced stability, reduced phase impurities, and lower processing sensitivity [27, 28]. These films remain thermally robust and less affected by solvent vapors, facilitating reproducible, large‑scale fabrication.

a Cross‑sectional SEM of Cs₀M, b Cs₅M, and c low‑magnification Cs₅M devices [27].

Graded Bandgap Perovskite Solar Cells

In 2016, researchers at UC Berkeley and LBNL introduced a graded‑bandgap design combining CH₃NH₃SnI₃ and CH₃NH₃PbI₃₋ₓBrₓ layers separated by a single‑atom h‑BN monolayer. The tandem device achieved a peak PCE of 26%, with steady‑state efficiency around 21.7% [29–31]. The architecture captures nearly the entire visible spectrum, yielding a time‑dependent performance that stabilizes after ~5 min of illumination.

a Schematic of graded‑bandgap PSC with GaN, h‑BN, and graphene aerogel. b Cross‑sectional SEM of representative device; layers and h‑BN not visible in SEM but identified via EDX. Scale bar 200 nm [29].

Stability of Perovskite Solar Cells

Despite efficiency gains, PSCs still face significant degradation under moisture, oxygen, UV exposure, and thermal stress. Recent studies highlight that humidity is the most critical factor, accelerating decomposition into PbI₂ and volatile methylammonium iodide [32–44].

a Proposed decomposition pathway of CH₃NH₃PbI₃ in presence of water. b Absorbance reduction vs. relative humidity. c PDS spectra showing absorption loss after exposure to 30–40% RH. d Degradation under moisture/air; UV‑vis spectra before/after exposure; inset photograph of CH₃NH₃I under various conditions [32].

Stability enhancement strategies include low‑temperature CeOₓ ETLs, mixed‑cation/mixed‑halide perovskites, carbon electrodes, and advanced encapsulation. For example, CeOₓ ETLs exhibit superior light‑soaking stability compared to TiO₂, while FA₀.₈₃Cs₀.₁₇Pb(I₀.₆Br₀.₄)₃ devices retain performance under full‑spectrum illumination without encapsulation [53–55].

Interface Engineering

Interface quality governs exciton dissociation, charge transport, and device longevity. Strategies such as chlorine‑capped TiO₂ colloidal nanocrystals and insulating tunneling layers between perovskite and ETL have achieved >20% certified efficiencies and 90% performance retention after 500 h at the maximum power point [57–58]. Computational studies further elucidate recombination pathways at charge‑selective contacts and grain boundaries [59].

Conclusions

Recent advances have propelled single‑junction PSC efficiencies above 22%, approaching crystalline silicon benchmarks. Halide perovskites now stand as a compelling, low‑cost alternative to conventional PV technologies. Nonetheless, long‑term stability remains the key hurdle. Continued progress in device architectures, material composition, and interface engineering promises to deliver highly stable, high‑performance PSCs ready for commercial deployment.